Modern Dictionary of Electronics

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MODERN DICTIONARY of

ELECTRONICS SEVENTH EDITION REVISED AND UPDATED

Rudolf F. Graf is an author whose name is well-known to engineers, technicians, and hobbyists around the world. He graduated as an electronics engineer from Brooklyn Polytechnic Institute and did his graduate work New York University. Mr. Graf has been active in the electronics industry for more than fifty years in capacities ranging from design and consulting engineer, chief engineer, chief instructor at electronics and television schools, and consulting editor. He also held various sales and marketing positions. h4r. Graf is the author or co-author of more than 150 technical articles published by major magazines. He has written about 50 books on electricity and electronics, with more than 2 million copies in print, including the best-selling Kdeo Scrambling & Descrambling for Satellite & Cable TV,Second Edition and the Circuits series of books, both published by Newnes. A number of his books have been translated into several European languages as well as Chinese, Japanese, and Russian.

MODERN DICTIONARY of

ELECTRONICS SEVENTH EDITION REVISED AND UPDATED

Rudolf F. Graf

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Library of Congress Cataloging-in-Publication Data Graf, Rudolf F. Modem dictionary of electronics / Rudolf F. Graf.-7th ed., revised and updated. p. cm. ISBN 0-7506-9866-7 (alk. paper) 1. Electronics -Dictionaries. I. Title TK7804.G67 1999 99-17889 621.381'03 -dc21 CIP British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. The publisher offers special discounts on bulk orders of this book. For information, please contact: Manager of Special Sales Butterworth-Heinemann 225 Wildwood Avenue Wobm, MA 01801-2041 Tel: 781-904-2500 Fax: 78 1-904-2620 For information on all Butterworth-Heinemann publications available, contact our World Wide Web home page at: http://www.bh.com 109 8 7 6 5 4 3 2 1 Typeset by Laser Words, Madras, India Printed in the United States of America

It gives me great pleasure to dedicate this edition to Allison, Sheryl, Daniel, David, Russell and Scott, the loveliest children this side of heaven.

When the first edition of this dictionary was published in 1961, today's everyday items like color TVs, VCRs, CD players, computers, FAX machines, ATMs, cordless and cell phones, pagers, tape recordeirs, digital watches, pocket calculators, lasers, and many others too numerous to mention, were non-existent or mere laboratory curiosities. Since then, electronics has undergone significant changes based primarily on the meteoric expansion of integrated circuits and their apparently limitless applications. Vacuum tubes were replaced by semiconductors, and numerous technologies like ferrite core or bubble memories were relegated to the electronics graveyard. No other industry has ever grown so much and matured so fast, paced by technological advances that occur at a feverish pace. The first edition of this dictionary contained about 10,000 definitions of then current terms. And now, a scant 38 years later, this seventh edition contains approximately 25,000 terms-a clear indication of the phenomenal growth of our industry. As technologies evolve and fresh products and concepts are introduced, suitable terminology must be developed to be able to communicate. The originators of the new words give them their initial meaning, but their exact definitions change with technological advances and through actual use by others. The contents of this dictionary is thus an analysis of words and their meanings as determined by common usage, written in a modern and popular style to provide clear and concise explanations of each entry. Continual updating of a work such as this is vital, so that those involved in the world of electronics have the power to communicate with those about them and to grasp new concepts as they emerge. All entries are allowed as much space as is necessary for complete and meaningful definitions. 'Terms are explained clearly and precisely without excessive technical jargon. Original entries from the previous edition have been reviewed and many were revised to keep pace with current usage. Where more than one definition exists for a term, they are arranged numerically. This method, however. does not necessarily imply a preferred order of meanings. Important words from formative technologies that are no longer in use are retained in this edition for their historical interest. My thanks go out to Ms. Tara Troxler Thomas and to Charles Thomas whose dedication to this project iind skill at the word processor made it possible to deliver the manuscript for this work to the ]publisher in a timely fashion. Industry and technical sources-notably the IEEE and the ASA-generously aided in defining many terms during the preparation of earlier editions of this work. While this volume is as up-to-date as possible at the time of writing, the field of electronics is expandiing so rapidly that new terms are constantly being developed and older terms take on broader or more specialized meanings. It is the intention of the publisher to periodically issue revised editions of this dictionary; thus suggestions for new terms and definitions are always welcome. Rudolf F. Graf February 1999

A

A- 1 , Abbreviation for angstrom unit, used in expressing wavelength of light. Its length is centimeter. 2. Chemical symbol for argon, an inert gas used in some electron tubes. 3. Letter symbol for area of a plane surface. 4. Letter symbol for ampere. a-Letter symbol for atto- (lo-''). A0 -'The Federal Communications Commission (FCC) designation for radio emission consisting solely of an unmodulated carrier. A1 -The FCC designation for radio emission consisting of a continuous-wave carrier keyed by telegraphy. A-1 or A.1-The atomic time scale maintained by the 1J.S. Naval Observatory; presently it is based 'on weighted averages of frequencies from cesium-beam 'devices operated at a number of laboratories. A2 -'The FCC designation for radio emission consisting of a tone-modulated continuous wave. A3-The FCC designation for radio emission consist.ing of amplitude-modulated speech transmission. A4--The FCC designation for radio emission consist-ing of amplitude-modulated facsimile signals. A5-The FCC designation for radio emission consist:ing of amplitude-modulated television video signals. A- (A-minus or A-negative) -Sometimes called F-. Negative terminal of an A battery or negative polarity of other sources of filament voltage. Denotes the terminal to which the negative side of the filament-voltage source should be connected. A+ (A,-plus or A-positive)-Sometimes called F+. Positive terminal of an A battery or positive polarity of other sources of filament voltage. The terminal to which the positive side of the filament voltage source should be connected. ab- -The prefix attached to names of practical electric units to indicate the corresponding unit in the cgs (centimetler-gram-second) electromagnetic system, e.g., abampere, abvolt, abcoulomb. abac -- See alignment chart. abampere -Centimeter-gram-second electromagneIic unit of current. The current that, when flowing through a wire 1 centimeter long bent into an arc with a radius of 1 centimeter, produces a magnetic field intensity of 1 oersted. One abampere is equal to 10 amperes. A battery- Source of energy that heats the filaments of vacuum tubes in batteryoperated equipment. abbreviated dialing- 1. A system using specialgrade circuits that require fewer than the usual number of dial pulses to connect two or more subscribers. 2. Ability of a phone system to require only two to four digits, while the network dials the balance of the seven to fourteen digits required. abc ---Also ABC. See automatic bass compensation. abcoulomb -Centimeter-gram-second electromagnetic unit of electrical quantity. The quantity of electricity

passing any point in an electrical circuit in 1 second when the current is 1 abampere. One abcoulomb is equal to 10 coulombs. aberration -1. In lenses, a defect that produces inexact focusing. Aberration may also occur in electron optical systems, causing a halo around the light spot. 2. In a cathode-ray tube, a defect in which the electron "lens" does not bring the electron beam to the same point of sharp focus at all points on the screen. 5. Failure of an optical lens to produce exact point-to-point correspondence between an object and its image. 4. Blurred focusing of light rays due to the difference in bending (refraction) imparted on different light frequencies (colors) as they pass through a lens. a b f a r a d -Centimeter-gram-second electromagnetic unit of capacitance. The capacitance of a capacitor when a charge of 1 abcoulomb produces a difference of potential of 1 abvolt between its plates. One abfarad is equal to lo9 farads. a b h e n r y -centimeter-gram-second electromagnetic unit of inductance. The inductance in a circuit in which an electromotive force of 1 abvolt is induced by a current changing at the rate of 1 abampere per second. One abhenry is equal to henry. a b m h o -Centimeter-gram-second electromagnetic unit of conductance. A conductor or circuit has a conductance of 1 abmho when a difference of potential of 1 abvolt between its terminals will cause a current of 1 abampere to flow through the conductor. One abmho is equal to lo9 mho. Preferred term: absiemens. abnormal glow-In a glow tube, a current discharge of such magnitude that the cathode area is entirely surrounded by a glow. A further increase in current results in a rise in its density and a drop in voltage. abnormal propagation -The phenomenon of unstable or changing atmospheric andlor ionospheric conditions acting on transmitted radio waves. Such waves are prevented from following their normal path through space, causing difficulties and disruptions of communications. a b n o r m a l reflections-See sporsldic reflections. abnormal termination -The shutdown of a computer program run or other process by the detection of an error by the associated hardware, indicating that some ongoing series of actions cannot be executed correctly. a b o h m -Centimeter-gram-second electromagnetic unit of resistance. The resistance of a conductor when, with an unvarying current of 1 abampere flowing through it, the potential difference between the ends of the conductor is 1 abvolt. One abohm is equal to ohm. abort-1. To cut short or break off (an action, operation, or procedure) with an aircraft, guided missile, or the like, especially because of equipment failure. An abort may occur at any point from start of countdown

AB power p a c k

- absolute tolerance

or takeoff to the destination. An abort can be caused by human technical or meteorological errors, miscalculation, or malfunctions. 2. The process of halting a computer program in an orderly fashion and returning control to the operator or operating system. 3. Abnormal termination of a computer program, caused by hardware or software malfunction or operator cancellation. AB power pack-Assembly in a single unit of the A and B batteries of a battery-operated circuit. Also, a unit that supplies the necessary A and B voltages from an ac source of power. abrasion m a c h i n e -A laboratory device for determining the abrasive resistance of wire or cable. The two standard types of machines are the squirrel cage with square steel bars and the abrasive grit types. abrasion resistance-A measure of the ability of a wire or wire covering to resist damage due to mechanical causes. Usually expressed as inches of abrasive tape travel. abrasion soldering -Soldering difficult metals by abrading the surface oxide film beneath a pool of molten solder. abrasive trimming -Trimming a ceramic capacitor or a film resistor to its nominal value by notching the surface with a finely adjusted stream of abrasive material such as aluminum oxide. abscissa-Horizontal, or x, axis on a chart or graph. absence-of-ground s e a r c h i n g selector-In dial telephone systems, an automatic switch that rotates, or rises vertically and rotates, in search of an ungrounded contact. absolute accuracy-1. The tolerance of the fullscale set point referred to as the absolute voltage standard. 2. Parameter for a d/a converter. It is the overall accuracy of the converter, in which all levels are compared with an absolute standard. Absolute accuracy includes the combination of all nonlinearity and end-point errors. absolute address-1. An address used to specify the location in storage of a word in a computer program, not its position in the program. 2. A binary number assigned permanently as the address of a storage location in a computer. 3. A fixed location in the memory of the CPU, as opposed to a relative address, which is specified according to its distance from another location. absolute altimeter- 1. Electronic instrument that furnishes altitude data with regard to the surface of the earth or any other surface immediately below the instrument, as distinguished from an aneroid altimeter, the readings of which depend on air pressure. 2. An altimeter that employs transmitted and reflected radio waves for its operation and thus does not depend on barometric pressure for its altitude indication. absolute code-A code using absolute addresses and absolute operation codes; that is, a code that indicates the exact location where the reference operand is to be found or stored. absolute coding-Coding written in machine language. It can be understood by the computer without processing. absolute delay-The time interval between the transmission of two synchronized radio, loran, or radar signals from the same or different stations. absolute digital position transducer-A digital position transducer, the output signal of which is indicative of absolute position. Also called encoder. absolute efficiency-Ratio of the actual output of a transducer to that of a corresponding ideal transducer under similar conditions. absolute error- 1. The amounts of error expressed in the same units as the quantity containing the error.

2 2. Loosely, the absolute value of the error, that is, the magnitude of the error without regard to its algebraic sign. absolute gain of an antenna-The gain in a given direction when the reference antenna is an isotropic antenna isolated in space. absolute instruction -A computer instruction that explicitly states, and causes the execution of, a specific operation. absolute language-The language in which instructions must be given to the computer. The absolute language is determined when the computer is designed. Synonyms: machine language, machine code. absolute loader--Program to load a computer program at specified numerical addresses. absolute maximum rating -Limiting values of operating and environmental conditions, applicable to any electron device of a specified type as defined by its published data and not to be exceeded under the worst probable conditions. Those ratings beyond which the life and reliability of a device can be expected to decline. absolute maximum supply voltage-The maximum supply voltage that may be applied without the danger of causing a permanent change in the characteristics of a circuit. absolute minimum resistance-The resistance between the wiper and the termination of a potentiometer, when the wiper is adjusted to minimize that resistance. absolute Peltier coefficient-The product of the absolute temperature and the absolute Seebeck coefficient of a material. absolute power -Power level expressed in absolute units (e.g., watts or dBm). absolute pressure transducer- 1. A pressure transducer that accepts two independent pressure sources simultaneously, and the output of which is proportional to the pressure difference between the sources. 2. A transducer that senses a range of pressures, which are referenced to a fixed pressure. The fixed pressure is normally total vacuum. absolute scale-See Kelvin scale. absolute S e e b e c k coefficient-The integral from absolute zero to the given temperature of the quotient of the Thomson coefficient of a material divided by its absolute temperature. absolute spectral response -Output or response of a device, in terms of absolute power levels, as a function of wavelength. absolute s y s t e m of units- Also called coherent system of units. A system of units in which a small number of units is chosen as fundamental, e.g., units of mass, length, time, and charge. Such units are termed absolute units. All other units are derived from them by taking a definite proportional factor in each of those laws chosen as the basic laws for expressing the relationships between the physical quantities. The proportional factor is generally taken as unity. absolute temperature-Temperature measured from absolute zero, a theoretical temperature level variously defined as -273.2”C, -459.7”F, or 0 K. absolute temperature scale-Thermodynamic temperature scale, named for Lord Kelvin (1848), in which temperatures are given in kelvins (K). (In the SI system the degree sign and the word degree are not used for Kelvin temperatures.) The absolute zero of temperature is 0 K, -273.2”C, or -459.7”F. The kelvin is the same size as the Celsius degree. a b s o l u t e tolerance- Also called accuracy. The maximum deviation from the nominal resistance (or capacitance) value, usually given as a percentage of the nominal value.

3

absolute units-A system of units based on physical principles, in which a small number of units are chosen as fundamental and all other units are derived from them; e.g., abohm, abcoulomb, abhenry, etc. absolute value-The numerical value of a number or symbol without reference to its algebraic sign. Thus, 3 is the ablsolute value of 131 or 1-31. An absolute value is signified by placing vertical lines around the number or symbol. absolute value device-A computing element that produces an output equal to the magnitude of the input signal, but always of one polarity. absolute zero-Lowest possible point on the scale of absolute temperature; the point at which all molecular activity ceases. Absolute zero is variously defined as -273.2”C, -459.7”F, or 0 K. absorbed wave-A radio wave that becomes lost in the ionosphere due to molecular agitation and the accompanying energy loss it undergoes there. Absorption is most pronounced at low frequencies. a b s o r b e r - I. In a nuclear reactor, a substance that absorbs neutrons without reproducing them. Such a substance may be useful in control of a reactor or, if unavoidably present, may impair the neutron economy. 2. Any material or device that absorbs and dissipates radiated energy. 3. In microwave terminology, a material or device thiat takes up and dissipates radiated energy. It may be used For shielding, to prevent reflection, or to transmit one or more radiation components selectively. absoirption -1. Dissipation of the energy of a radio or sound wave into other forms as a result of its interaction with matter. 2. The process by which the number of particles or photons entering a body of matter is reduced by interaction of the particle or radiation with matter. Similarly, the reduction of the energy of a particle while traversing a body of matter. This term is sometimes erroneously used for capture. 3. Penetration of a substance into the body of another. 4. Conversion of radiant energy into other forms by passage through, or reflection from, matter. 5. The adhesion of a fluid in extremely thin layers to the surfaces of a solid. 6. Reduction in strength of an electromagnetic wave propagating through a medium, determined by dielectric properties of the material. ttenuation-Loss in an optical fiber impurities, including metals, such as and iron, as well as OH ions. ircuit -A tuned circuit that dissipates energy taken from another circuit or from a signal source. This effect is especially evident in a resonant circuit such as a wavemeter or wave trap.

absorption coefficient- 1. Measure of soundabsorbing characteristics of a unit area of a given material compared with the sound-absorbing characteristics of an open space (total absorption) having the same area. 2. Ratio of loss of intensity caused by absorption to the total original intensity of radiation. absorption current-The current flowing into a capacitor following its initial charge, due to a gradual

absolute units - abvolt penetration of the electric stress into the dielectric. Also, the current that flows out of a capacitor following its initial discharge. absorption dynamometer-An instrument for measuring power, in which the energy of a revolving wheel or shaft is absorbed by the friction of a brake. absorption fading-A slow type of fading, primarily caused by variations in the absorption rate along the radio path. absorption f r e q u e n c y meter-See absorption wavemeter. absorption loss- 1. That part of transmission loss due to dissipation or conversion of electrical energy into other forms ( e g , heat), either within the medium or attendant upon a reflection. 2. The loss of optical flux or energy caused by impurities in the transmission medium as well as intrinsic material absorption. Expressed in decibels per kilometer. absorption m a r k e r -1. A sharp dip on a frequencyresponse curve due to the absorption of energy by a circuit sharply tuned to the frequency at which the dip occurs. 2. A small pip or blank introduced on an oscilloscope trace to indicate a frequency point. It is so called because it is produced by a frequency-calibrated tuned trap similar to an absorption wavemeter. absorption modulation -Also called loss modulation. A system for amplitude-modulating the output of a radio transmitter by means of a variable-impedarxe device (such as a microphone semiconductor or vacuum-tube circuit) inserted into or coupled to the output circuit. absorption trap- A parallel-tuned circuit coupled either magnetically or capacitively to absorb and attenuate interfering signals. absorption wavemeter- Also called absorption frequency meter. An instrument for measuring frequency. Its operation depends on the use of a tuned electrical circuit or cavity loosely coupled inductively to the source. Maximum energy will be absorbed at the resonant frequency, as indicated by a meter or other device. Frequency can then be determined by reference to a calibrated dial or chart. absorptivity-A measure of the portion of incident radiation or sound energy absorbed by a material. abstraction -A simplified description or specification of a system that emphasizes some of the system’s details or properties while suppressing others. A high level of abstraction or a highly abstract machine is one in which very few machine details are apparent to a programmer, who sees only a broad set of machine concepts. Abstract machines are created by surrounding a primitive machine with layers of operating systems. To converse with higher levels of abstract machines, the user needs higher levels of languages. A/B s w i t c h -A switch that selects one of two inputs (A or €3) for routing to a common output while providing adequate isolating between the two signals. A-B test- 1. Direct comparison of two sounds by playing first one and then the other. May be done with two tape recorders playing identical kpes (or the same tape), two speakers playing alternately from the same tape recorder, or two amplifiers playing alternately through one speaker, etc. 2. An audio comparison test for evaluating the relative performance of two or more components or systems by quickly changing from one to the other. The left- and right-hand channels or the record and replay sound signals are often designated A and B. A and B test facilities are installed at most high-fidelity dealers. abvolt -Centimeter-gram-second electromagnetic unit of potential difference. The potential difference between two points when 1 erg of work is required to

ac - acceptor transfer 1 abcoulomb of positive electricity from a lower to a higher potential. An abvolt is equal to lo-* volt. ac -Abbreviation for alternating current. ac bias-The alternating current, usually of a frequency several times higher than the highest signal frequency, that is fed to a record head in addition to the signal current. The ac bias serves to linearize the recording process. accelerated aging -A test in which certain parameters, such as voltage and temperature, are increased above normal operating values to obtain observable deterioration in a relatively short period. The plotted results give expected service life under normal conditions. Also called accelerated life test. accelerated g r a p h i c s port -Abbreviated AGP. A slot inside PCs for high speed video to be used instead of the standard slot type, called PCI. accelerated life test -Test conditions used to bring about, in a short time, the deteriorating effect obtained under normal service conditions. accelerated service test-A service or bench test in which some service condition, such as speed, temperature, or continuity of operation, is exaggerated to obtain a result in a shorter time than that which elapses in normal service. accelerating conductor or relay-A conductor or relay that causes the operation of a succeeding device to begin in the starting sequence after the proper conditions have been established. acceleratingelectrode-An electrode in a cathoderay or other electronic tube to which a positive potential is applied to increase the velocity of electrons or ions toward the anode. A klystron tube does not have an anode but does have accelerating electrodes. accelerating time -The time required for a motor to reach full speed from a standstill (zero speed) position. accelerating voltage-A high positive voltage applied to the accelerating electrode of a cathode-ray tube to increase the velocity of electrons in the beam. acceleration-1. The rate of change in velocity. Often expressed as a multiple of the acceleration of gravity (g = 32.2 ft/s2). 2. The rate of change in velocity of a stepping motor measured in rads; it is the result of rotor torque divided by rotor and load inertia. 3. A vector quantity that specifies rate of change of velocity. acceleration at stall -The value of servomotor angular acceleration calculated from the stall torque of the motor and the moment of inertia of the rotor. Also called torque-to-inertia ratio. acceleration time -In a computer, the elapsed time between the interpretation of instructions to read or write on tape and the possibility of information transfer from the tape to the internal storage, or vice versa. acceleration torque-Numerical difference between motor torque produced and load torque demanded at any given speed during the acceleration period. It is this net torque that is available to change the speed of the driven load. acceleration voltage -Potential between a cathode and anode or other accelerating element in a vacuum tube. Its value determines the average velocity of the electrons. accelerator-A device for imparting a very high velocity to charged particles such as electrons or protons. Fast-moving particles of this type are used in research or in studying the structure of the atom itself. 2. A circuit that speeds up a computer or monitor. Typically a circuit card with an extra processing chip and/or additional RAM. accelerator board -An adapter with a microprocessor that makes a computer run faster.

accelerator d y n a m i c test -A test performed on an accelerometer by means of which information is gathered pertaining to the overall behavior frequency response and/or natural frequency of the device. accelerometer- 1. An instrument or device, often mounted in an aircraft, guided missile, or the like, used to sense accelerative forces and convert them into corresponding electrical quantities, usually for measuring, indicating, or recording purposes. It does not measure velocity or distance, only changes in velocity. 2. A transducer that measures acceleration and/or gravitational forces capable of imparting acceleration. 3. A sensor whose electrical output is proportional to acceleration. TO INTEGRATORS

MASS

Accelerometer.

accentuation-Also called preemphasis. The emphasizing of any certain band of frequencies, to the exclusion of all others, in an amplifier or electronic device. Applied particularly to the higher audio frequencies in frequency-modulated (FM)transmitters. accentuator- 1. Network or circuit used for preemphasis, that is, an increase in amplitude of a given band of usually audible frequencies. 2. A circuit or device, such as a filter, tone control, or equalizer, used to emphasize a band of frequencies, usually in the audio-frequency spectrum. acceptable-environmental-range test-A test to determine the range of environmental conditions for which an apparatus maintains at least the minimum required reliability. acceptable quality level -Abbreviated AQL. The maximum percentage of defective components considered to be acceptable as an average for a process or the lowest quality a supplier is permitted to present continually for acceptance. Also see AQL. acceptance angle-1. The solid angle within which all incident light rays will enter the core of an optical fiber. Expressed in degrees. 2. In fiber optics, a measure of the maximum angle within which light may be coupled from a source or emitter. It is measured relative to the fiber’s axis. 3. The critical angle, measured from the core centerline, above which light will not enter an optical fiber. It is equal to the half-angle of the acceptance cone. 4. The maximum angle within which light will be accepted by an element, such as a detector. acceptance cone- 1. A parameter that defines acceptable light-launching angles. Only light launched at angles within this cone will be waveguided (fiber optics). 2. A cone with an included angle twice that of the acceptance angle. acceptance pattern-In fiber optics, a curve of total transmitted power plotted against the launch angle. acceptance sampling plan-A plan for the inspection of samples as a basis for acceptance or rejection of a lot. acceptor- Also called acceptor impurity. An impurity lacking sufficient valence electrons to complete the

5 bonding arrangement in the crystal structure. When added to a semiconductor crystal, it accepts an electron from a neighboring atom and thus creates a hole in the lattice structure of the crystal, making a p-type semiconductor. 2. An impurity from column I11 of the periodic table, which adds a mobile hole to silicon, thereby making it more p-type and accepting of electrons. Boron is the primary acceptor used to dope silicon (compare with donor). acceptor circuit- 1. A circuit that offers minimum oppositioln to a given signal. 2. A circuit tuned to respond to a single frequency. acceptor impurity-See acceptor. acceptor-type semiconductor -A p-type semiconductor. access- 1. To gain access to a computer’s memory location in which binary information is already stored or can be stored. 2. To open up a set of connections to allow reading from or writing into this location. access arm-In a computer storage unit, a mechanical device that positions the reading and writing mechanism. access code- 1. The preliminary digit or digits that a telephone user must dial to be connected to a particular outgoing trunk group. 2. A group of characters or numbers that identifies a user to a computer or any other secure system. 3. One or more numbers and/or symbols that are keyed into the repeater with a telephone tone pad to activate a repeater function, such as an autopatch. access control-1. The control of pedestrian and vehicular traffic through entrances and exits of a protected area or premises. 2. The process of limiting access to resources of a system to only authorized users, programs, processes, or other systems. access grant -Multiprocessor system response that satisfies a previous service request. access hole-A hole drilled through successive layers of a multilayer board to gain access to a land or pad location on one of the inside layers. access method- 1. A data-management technique available for use in transferring data between the main storage and an input/output device. 2. A software component of a computer operating system that controls the flow #ofdata bletween application programs and either local or remote peripheral devices. access mode- 1. A technique used in COBOL to obtain a specific logic record from, or to place it into, a file ,assignedto a mass storage device. 2. The operation of an #alarmsystem such that no alarm signal is given when the protected area is entered; however, a signal may be given .if the sensor, annunciator, or control unit is tampered with lor opened. acce6sory card -An additional circuit card that can Ibe mounted inside a personal computer and connected to ihe system bus. access protocol-A defined set of procedures that -Function as an interface between a computer user and a network, enabling the user to employ the services of that network. access provider -Telecommunications company !hat links businesses and individuals to the Internet using imodem devices, high-speed ISDN lines, or dedicated links. ac6ess time-Also called waiting time. 1. The itime interval (called read time) between the instant of calling for data from a storage device and the instant fief completion of delivery. 2. In a memory system, the itime delay, at specified thresholds, from the presentation of an enable or address input pulse until the arrival of the memory data output. 3. The time required for a (computerto move data between its memory section and its

acceptor circuit

- accuracy

CPU. 4. A time interval that is characteristic of a storage device. Essentially, it is a measure of the time required to communicate with that device, or, more specifically, it is the time between the application of a specified input pulse (assuming that other necessary inputs are also present) and the availability of valid data signals at an output. The access time can be defined only with reference to an output signal. 5. The time required by a computer to begin delivering information after the memory or storage has been interrogated. 6. The time it takes a computer to retrieve a piece of information. With hard disks or compact discs, maximum access time is measured as the time it takes to move from one end of the disk to the other, find a piece of information, and transfer that information to RAM. accidental jamming -Jamming caused by transmission from friendly equipment. ac circuit breaker-A device that is used to close and interrupt an ac power circuit under normal conditions or to interrupt this circuit under faulty or emergency conditions. accompanying audio (sound) channel -Also known as co-channel sound frequency. The rf canier frequency that supplies the sound to accompany a television picture. ac component-In a complex wave (i.e., one containing both ac and dc), the alternating, fluctuating, or pulsating member of the combination. accordion-A type of contact used in some printedcircuit connectors. The contact spring is given a z shape to permit high deflection without excessive stress. ac-coupled flip-flop-A flip-flop that changes state when triggered by the rise or fall of a clock pulse. There is a maximum allowable rise or fall time for proper triggering. ac coupling-Coupling of one circuit to another circuit through a capacitor or other device that passes the varying portion but not the static (dc) characteristics of an electrical signal. accumulationkey-In a calculator, it automatically accumulates products and totals of successive calculations. accumulator- 1. In an electronic computer, a device which stores a number and which, on receipt of another number, adds the two and stores the sum. An accumulator may have properties such as shifting, sensing signals, clearing, complementing, etc. 2. A chemical cell able to store electrical energy (British). Also called secondary cell. 3. The “scratch pad” section of the computer, in which arithmetic operations are carried out. 4. A register and related circuitry that hold an operand for aithmetic and logic operations. 5. A register or latch internal to the MPU where data is stored temporarily before being sent to another location internal or external to the MPU chip. accuracy- 1. The maximum error in the measurement of a physical quantity in terms of the output of an instrument when referred to the individual instrument calibration. Usually given as a percentage of full scale. 2. The quality of freedom from mistake or error in an electronic computer, that is, of conformity to truth or to a rule. 3. The closeness with which a measured quantity approaches the true value of that quantity. (See true value.) 4. The degree to which a measured or calculated value conforms to the accepted standard or rule. 5. The measure of a meter’s ability to indicate a value corresponding to the absolute value of electrical energy applied. Accuracy is expressed as a percentage of the meter’s rated full-scale value. To be meaningful, accuracy specifications must always consider the effects of time, temperature, and humidity. 6. Confidence in the correlation between measurements in one location and another,

accuracy rating of an instrument - acorn tube or between a measurement and a recognized standard. 7. The correctness or certainty of position when the rotor of a stepping motor comes to rest. It is usually expressed as a percentage of the step angle, but can also be specified in degrees or minutes of arc. In steppers, the error is not cumulative, but occurs only at the completion of the last step. 8. The degree of freedom from error, that is, the degree of conformity to some standard. Accuracy is contrasted with precision. For example, four-place numbers are less precise than six-place numbers; however, a properly computed four-place number might be more accurate than an improperly computed six-place number. 9. As applied to an adc, the term describes the difference between the actual input voltage and the full-scale weighted equivalent of the binary code. a c c u r a c y rating of an instrument-The limit, usually expressed as a percentage of full-scale value, not exceeded by errors when the instrument is used under reference conditions. ACD -Abbreviation for automatic call distributor. A switching system that automatically distributes incoming calls to a centralized group of receivers in the sequence in which the calls are received. It holds calls until a receiver is available. ac/dc -Electronic equipment capable of operation from either an ac or dc primary power source. Abbreviation for alternating currenVdirect current. ac/dc receiver-A radio receiver designed to operate directly from either an ac or a dc source. ac/dc ringing-A method of telephone ringing in which alternating current is used to operate a ringing device, and direct current is used to aid the action of a relay that stops the ringing when the called party answers. ac directional overcurrent relay-A device that functions on a desired value of ac overcurrent flowing in a predetermined direction. ac dump -The intentional, accidental, or conditional removal of all alternating-current power from a system or component. An ac dump usually results in the removal of all power, since direct current is usually supplied through a rectifier or converter. ac erasing h e a d -In magnetic recording, a device using alternating current to produce the magnetic field necessary for removal of previously recorded information. acetate-A basic chemical compound in the mixture used to coat recording discs. acetate base -The transparent plastic film that forms the tough backing for acetate magnetic recording tape. acetate disc- A mechanical recording disc, either solid or laminated, made mostly from cellulose nitrate lacquer plus a lubricant. acetate tape -A sound-recording tape with a smooth, transparent acetate backing. One side is coated with an oxide capable of being magnetized. ac generator- 1. A rotating electrical machine that converts mechanical power into alternating current. Also known as an alternator. 2. A device, usually an oscillator, designed for the purpose of producing alternating current. A channel-One of two stereo channels, usually the left. achieved reliabili@-Reliability determined on the basis of actual performance of nominally identical items under equivalent environmental conditions. Also called operational reliability. a c h r o m a t i c - 1. In color television, a term meaning a shade of gray from black to white, or the absence of color (without color). 2. Black-and-white television, as distinguished from color television. 3. Literally, color free. In an optical system, the term is used when chromatic aberration is corrected for at least two wavelengths. A

6 color that is defined as being achromatic is often referred to as gray. 4. Having no color; being a neutral such as black, white, or gray. a c h r o m a t i c lens-A lens that has been corrected for chromatic aberration. Such a lens is capable of bringing all colors of light rays to approximately the same point of focus by combining a concave lens of flint glass with a convex lens of crown glass. A lens that transmits light without separating it into its constituent colors. a c h r o m a t i c locus- Also called achromatic region. On a chromaticity diagram, an area that contains all points representing acceptable reference white standards. a c h r o m a t i c region-See achromatic locus. acicular-Needle-shaped; descriptive of the shape of the magnetizable particles composing the coating of a recording tape. Modern tapes are premagnetized during the coating process to line the “needles” up with the direction of the tape, thus providing maximum sensitivity from the oxide. acid -A chemical compound that dissociates and forms hydrogen ions when in aqueous solution. acid depolarizer-An acid, such as nitric acid, sometimes introduced into a primary cell to prevent polarization. acid fluxes-Fluxes consisting of inorganic acids and salts, which are used when a surface to be soldered is below the ideal for rapid wetting. Also called corrosive fluxes. acknowledge-A control signal used to complete a handshaking sequence in telecommunications. The acknowledge signal indicates that the information has been accepted by the receiving computer. ac line -A power line delivering alternating current only. ac line filter-A filter designed to dissipate or bypass to ground any extraneous signals or electrical noise on an ac power line, while causing virtually no reduction of the power-line voltage or power. Used to keep unwanted signals and noise out of sensitive equipment. aclinic line-Also called isoclinic line. On a magnetic map, an imaginary line that connects points of equal magnetic inclination or dip. ac magnetic biasing -In magnetic recording, the method used to remove random noise and/or previously recorded material from the wire or tape. This is done by introducing an alternating magnetic field at a substantially higher frequency than the highest frequency to be recorded. ac noise-Noise that displays a rate of change that is fast relative to the response capability of the device. ac noise immunity-A measure of a logic circuit’s ability to maintain the prescribed logic state in the presence of such noise. It is defined in terms of the amplitude and pulse width of an input noise signal to which the element will not respond. acorn tube -A button- or acorn-shaped vacuum tube with no base, designed for UHF applications. Electrodes are brought out through the glass envelope on the side, top, and bottom.

Acorn tube.

7 acoustic- Also acoustical. Pertaining to sound or the science of sound. acoustic absorption loss-The energy lost by conversion into heat or other forms when sound passes through or is reflected by a medium. acoustic absorptivity -The ratio of sound energy absorbed by a surface to the sound energy arriving at the surface. Equal to 1 minus the reflectivity of the surface. acoustical-See acoustic. acoustical attenuation constant-The real part of the arcoustical propagation constant. The commonly used unit is the neper per section or per unit distance. acoustical coupler-A device for connecting a telephone handset to a computer input port. acoustical-electrical transducer-A device designed to transform sound energy into electrical energy and vice versa. acoustical material-Any material considered in terms of its acoustical properties; especially, a material designedl to absorb sound. acoustical mode -A mode of crystal-lattice vibration that does not produce an oscillating dipole. acoustical ohm -A measure of acoustic resistance, reactance, or impedance. One acoustical ohm is equal to a volume velocity of 1 cubic centimeter per second when produced by a sound pressure of 1 microbar. acoustical phase constant-The imaginary part of the acoustical propagation constant. The commonly used unit is the radian per section or per unit distance. coustical reflectivity-See sound-reflection coefficient. acousticaltransmittivity-See sound-transmission coefficient. acoustic burglar alarm -Also called acoustic intrusion detector. A burglar alarm that is responsive to sounds produced by an intruder. Concealed microphones connected to an audio amplifier trip an alarm when sounds within a predetermined range of frequencies exceed a predetermined normal level. acoustic capacitance-In a sound medium, a measure of volume displacement per dyne per square centimetler. The unit is centimeter to the fifth power per dyne. acoustic clarifier-A system of cones loosely attached to the baffle of a speaker and designed to vibrate and absorb energy during sudden loud sounds, thereby suppressing them. acou~sticcompliance- 1. The measure of volume displacement of a sound medium when subjected to sound waves. 2. That type of acoustic reactance which corresponds to capacitive reactance in an electrical circuit. acoustic coupler- 1. A device that converts digital signals into audio signals, enabling data to be transmitted over the telephone lines via a conventional telephone. 2. A modem device that connects a terminal or computer to the handset of a telephone. acoustic coupling --Coupling resonator elements by mechanical means through the use of wires, rods, or nonelecboded sections of quartz or ceramic. The terms acoustic and mechanical can be used interchangeably. acoustic delay line--A device that retards one or more signal vibrations by causing them to pass through a solid or liquid. acoustic dispersion -The change of the speed of sound with frequency. acoustic elasticity- 1. The compressibility of the air in a speaker enclosure as the cone moves backward. 2. The compressibility of any material through which sound is passed.

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Acoustic coupler.

acousticfeedback- 1. Also called acoustic regeneration. The mechanical coupling of a portion of the sound waves from the output of an audio-amplifying system to a preceding part or input circuit (such as the microphone) of the system. When excessive, acoustic feedback will produce a howling sound in the speaker. 2. The pickup, by a turntable, of vibrations from the speaker. If these vibrations reach the cartridge, they will be reamplified, causing noise (usually a rumble, but in extreme cases a howl) and/or distortion. Also, feedback resulting from such sound waves setting some part of an amplifier circuit into vibration and thus modulating the currents in the circuit. Acoustic feedback usually causes howling or whistling. acoustic filter- 1. A sound-absorbing device that selectively suppresses certain audio frequencies while allowing others to pass. 2. Any sound-absorbing or soundtransmitting arrangement, or combination of the two, that passes sound waves of desired frequency while attenuating or eliminating others. acoustic frequency response-The voltageattenuation frequency measured into a resistive load, producing a bandwidth approaching sufficiently close to the maximum. acoustic generator-A transducer, such as a speaker, headphones, or a bell, that converts electrical, mechanical, or other forms of energy into sound. acoustic homing system-1. A system that uses a sound signal for guidance purposes. 2. A guidance method in which a missile homes in on noise generated by a target. acoustic horn-Also called horn. 1. A tube of varying cross section having different terminal areas that change the acoustic impedance to control the directivity of the sound pattern. 2. A tapered tube (round or rectangular, but generally funnel shaped) that directs sound and, to some extent, amplifies it. acoustic impedance- 1. Total opposition of a medium to sound waves. Equal to the force per uait area on the surface of the medium divided by the flux (volume velocity or linear velocity multiplied by area) through that surface. Expressed in ohms and equal to the mechanical impedance divided by the square of the surface area. One unit of acoustic impedance is equal io a volume velocity of 1 cubic centimeter per second produced by a pressure of 1 microbar. Acoustic impedance contains both acoustic resistance and acoustic reactance. 2. The degree of resistance to transmitting sound imparted by the characteristic elasticity of a given substance. acoustic inertance-A type of acoustic reactance that corresponds to inductive reactance in an electrical circuit. (The resistance to movement or reactance offered by

acoustic intensity - acoustic transmission the sound medium because of the inertia of the effective mass of the medium.) Measured in acoustic ohms. acoustic intensity-The limit approached by the quotient of acoustical power being transmitted at a given time through a given area divided by the area as the area approaches zero. acoustic interferometer- An instrument for measuring the velocity or frequency of sound waves in a liquid or gas. This is done by observing the variations of sound pressure in a standing wave, established in the medium between a sound source and a reflector, as the reflector is moved or the frequency is varied. acoustic intrusion detector-See acoustic burglar alarm. acoustic labyrinth -A loudspeaker enclosure in which the rear of the loudspeaker is coupled to a tube which, at the resonant frequency of the loudspeaker, is one quarter of a wavelength long. The tube, folded upon itself in order to save space, gives the appearance of a labyrinth. acoustic lens- 1. An array of obstacles that refract sound waves in the same way that an optical lens refracts light waves. The dimensions of these obstacles are small compared with the wavelengths of the sounds being focused. 2. A device that produces convergence or divergence of moving sound waves. When used with a loudspeaker, the acoustic lens widens the beam of the higher-frequency sound waves. acoustic line-Mechanical equivalent of an electrical transmission line. Baffles, labyrinths, or resonators are placed at the rear of a speaker to help reproduce the very low audio frequencies. acoustic memory-A computer memory using an acoustic delay line. The line employs a train of pulses in a medium such as mercury or quartz. acoustic mine-Also called sonic mine. An underwater mine that is detonated by sound waves, such as those from a ship’s propeller or engines. acoustic mirage-The distortion of a sound wavefront by a large temperature gradient in air or water. This creates the illusion of two sound sources. acoustic ohm-The unit of acoustic resistance, reactance, or impedance. One acoustic ohm is present when a sound pressure of 1 dyne per square centimeter produces a volume velocity of 1 cubic centimeter per second. acoustic p h a s e constant-The imaginary part of the acoustic propagation constant. The commonly used unit is the radian per section or per unit distance. acoustic phonograph-A mechanical record player (now obsolete) in which the needle sets a thin diaphragm into vibration. The diaphragm in turn causes the air in a horn to vibrate, thus reproducing the recorded sound. acoustic pickup -1. In nonelectrical phonographs, the method of reproducing the material on a record by linking the needle directly to a flexible diaphragm. 2. In an acoustic phonograph, a pickup consisting of a needle, needle holder, and vibrating diaphragm. acoustic radiator-In an electroacoustic transducer, the part that initiates the radiation of sound vibration. A speaker cone or headphone diaphragm is an example. acoustic radiometer -An instrument for measuring sound intensity by determining the unidirectional steady-state pressure caused by the reflection or absorption of a sound wave at a boundary. acoustic reactance-That part of acoustic impedance due to the effective mass of the medium, that is, to the inertia and elasticity of the medium through which

8 the sound travels. The imaginary component of acoustic impedance; expressed in acoustic ohms. acoustic reflectivity-The ratio of the rate of flow of sound energy reflected from the surface on the side of incidence to the incident rate of flow. acoustic refraction-A bending of sound waves when passing obliquely from one medium to another in which the velocity of sound is different. acoustic regeneration -See acoustic feedback. acoustic resistance-That component of acoustic impedance responsible for the dissipation of energy due to friction between molecules of the air or other medium through which sound travels. Measured in acoustic ohms and analogous to electrical resistance. acoustic resonance -An increase in sound intensity as reflected waves and direct waves that are in phase combine. May also be due to the natural vibration of air columns or solid bodies at a particular sound frequency. acoustic resonator -An enclosure that intensifies those audio frequencies at which the enclosed air is set into natural vibration. acoustics-1. Science of production, transmission, reception, and effects of sound. 2. In a room or other location, those characteristics that control reflections of sound waves and thus the sound reception in it. acoustic scattering -The irregular reflection, refraction, or diffraction of a sound wave in many directions. acoustic shock-Physical pain, dizziness, and sometimes nausea brought on by hearing a loud, sudden sound. (The threshold of pain is about 120 dBm.) acoustic surface-wave component -A passive electroacoustic device that has metallized interdigital transducer elements deposited on the surface of a piezoelectric substrate. The device allows acoustic energy to be generated, manipulated, and detected on the substrate surface. Most of the acoustic energy is confined to a region within one wavelength of the surface of the substrate. When the metallization is subjected to an alternating voltage, a strain develops between the interdigital fingers and also at the frequency of excitation. This alternating strain on the crystal surface launches a Rayleigh surface-wave front that travels in both directions and that originates from the center of the transducer. The wave exists as an electroacoustic vibration. acoustic suspension- 1. A loudspeaker system in which the moving cone is held by an overcompliant suspension, the stiffness required for proper operation being supplied by air that is trapped behind the cone in a sealed enclosure. While relatively inefficient, such a system permits good bass reproduction in a unit of moderate size. 2. A speaker enclosure design in which the speaker cone is suspended in an airtight box. This enables the acoustic pressure of the air enclosed therein to provide the principal restoring force for the diaphragm of the speaker. It needs somewhat more power from the amplifier than a free speaker but has better low-frequency performance. acoustic system -Arrangement of components in devices designed to reproduce audio frequencies in a specified manner. acoustic telemetry-The utilization of sound energy for the transmission of information. It differs from other telemetry methods in that information derived from the received signal is encoded by the transmitting source. acoustic transformer-A device that transmits power along a glass or ceramic rod and isolates the power supply from the signal input. acoustic transmission -Direct transmission of sound energy without the intermediary of electric currents.

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acoustic transmission system -An assembly of elements adapted for the transmission of sound. acoustic treatment -Use of certain soundabsorbing materials to control the amount of reverberation in a room, hall, or other enclosure; that is, to make the room 1es;slive. acoustic wave -A traveling vibration by which sound energy is transmitted in air, water, or the earth. The characteristics of these waves may be described in terms of change of pressure, particle displacement, or density. acoustic wave fitter-A device designed to separate sound waves of different frequencies. (Through electroacoustic transducers, such a filter may be associated with electric circuits.) acoustoelectric effect-Generation of an electric current in a crystal by a traveling longitudinal sound wave. acousto-optic Bragg cell -A modulation device that impiresses analog information on light beams. This transducer is composed of two sets of interleaved electrodes off alternating polarities deposited on an optical waveguide. An electrical signal applied to each pair of adjacent electrodes buckles the film between them. This distortion changes the refractive index of the waveguide and creates physical waves in the film, commonly called surface waves. These waves are generated at a rate equal to that of the applied electrical signal. acousto-optics -The study of the interactions between sound waves and light in a solid medium. Sound waves can be made to modulate, deflect, and focus light waves - an important characteristic in laser and holographic applications. ac plate resistance- Also called dynamic plate resistanae. Internal resistance of a vacuum tube to the flow of alternating current. Expressed in ohms, the ratio of a small change in plate voltage to the resultant change in plate current, other voltages being held constant. ac power supply-A power supply that provides one or more ac output voltages, e.g., ac generator, dynamotsor, inverter, or transformer. acquiisitiosl- 1. The process of pointing an antenna or telescope so that it is properly oriented to allow gathering of tracking or telemetry data from a satellite or space probe. 2. In radar, the process between the initial location of a target and the final alignment of the tracking equipment on the target. 3. The gathering of data from transducers or a computer. cquisition and tracking radar-A radar set that locks onto a strong signal and tracks the object emitting or reflecting the signal. May be airborne or on the ground. ‘Tracking radars use a dish-type antenna reflector to produce a searchlight-type beam. acquiisition radar-A radar set that detects an approaching target and feeds approximate position data to a fire-control or missile-guidance radar, which then takes over the function of tracking the target. a c q u i ~ ~ trangei~n Also called capture range. The range of input hequency about f under which a phaselocked loop, which is initially unlocked, will become locked. This range is narrower than the normal tracking range and is a function of the loop-filter characteristics and the input amplitude. ~ c ~ u itimes ~ t1. ~ Time ~ delay ~ between request for data conversion and the holding of the analog value by a saniple-and-hold amplifier. 2. In a sample-and-hold circuit, how long it takes after the sample command is given f o r the hold capacitor to be charged to a full-scale voltage change and to remain within a specified error band around its final value. 3. The time it takes for the output of a sample-and-hold circuit to change from its previous value to a new value when the circuit is switched from the hold mode to the sample mode. It includes the slew

acoustic transmission s y s t e m - activation time and settling time to within a certain error band of the final value and is usually specified for a full-scale change. ac receiver -A radio receiver designed to operate from an ac source only. ac reclosing relay-A device that Controls the automatic reclosing and locking out of an ac circuit interrupter. ac relay-A relay designed to operate from an alternating-current source. ac resistance-Total resistance of a device in an ac circuit. See also high-frequency resistance. a c r o n y m -A word formed from the first letrer or letters of the words describing some item, e.g., FORTRAN from formula translation. across-the-line starting -Connection of a motor directly to the supply line for starting. Also called fullvoltage starting. ac signaling-Using ac signals or tones to transmit data and/or control signals. ACTCRBS -Abbreviation for air traffic control radar beacon system. A control system in use worldwide. Air separation infomation exchanged between plane and air traffic controller must be sent by radio. ac time overcurrent relay-A device that has either a definite or an inverse time characteristic and functions when the current in an ac circuit exceeds a predetermined value. actinic--In radiation, the property of producing a chemical change, such as the photographic action of light. actinium -A radioactive element discovered in pitchblende by the French chemist Debierne in 1889.Its atomic number is 89, its atomic weight 227, and its symbol Ac. actinodielectric-A photoconductive dielectric. actinoelectric-Exhibiting a temporary rise in electrical conductivity during exposure to light. actinoelectric effect- 1. The property of some special materials whereby when an electric current is impressed on them, their resistance changes with light. 2. The property of certain materials (such as selenium, cadmium sulfide, germanium, and silicon) that causes them to change their electrical resistance or generate a voltage on exposure to light. actinoelectricity-Electricity produced by the action of radiant energy on crystals. actinometer -An instrument that measures the intensity of radiation by detemining the amount of fluorescence produced by that radiation. action area-In the rectifying junction of a metallic rectifier, that portion which carries the forward current. action current-A brief and very small electric current that flows in a nerve during a nervous impulse. action potential -1. The instantaneous value of the voltage between excited and resting portions of an excitable living structure. 2. The voltage variations in a nerve or muscle cell when it is excited or fired by an appropriate stimulus. After a short tim-e, the cell recovers its normal resting potential, typically about 80 millivolts. The interior of the cell is negative relative to the outside. activate-To start an operation, usually by application of an appropriate enabling signal. activating-1. Chemically treating a basic metal to remove oxides and other passive films to make it more receptive to electroplating. 2. A treatment that renders nonconductive material receptive to electroless deposition. (Nonpreferred synonyms: seeding, catalyzing, and sensitizing.) activation - 1. Making a substance artificially radioactive by placing it in an accelerator such as a cyclotron or by bombarding it with neutrons. 2. To treat the cathode or target of an electron tube in order to create or increase its

activation time - a c t i v e matrix emission. 3. The process of adding electrolytes to a cell to make it ready for operation. 4. Causing the acceleration of a chemical reaction. activation time-In a cell or battery, the time interval from the moment activation is initiated to the moment the desired operating voltage is obtained. activator- An additive that improves the action of an accelerator. active- 1. Controlling power from a separate supply. 2. Requiring a power supply separate from the controls. 3. Containing, or connected to and using, a source of energy. active area-The portion of the rectifying junction of a metallic rectifier that carries forward current. active b a l a n c e -In operation of a telephone repeater, the summation of all return currents at a terminal network balanced against the local circuit or drop impedance. active circuit-A circuit that contains active elements such as transistors, diodes, or integrated circuits. active communications satellite-A communications satellite in which on-board receivers and transmitters receive signals beamed at them from a ground terminal, amplify them greatly, and retransmit them to another ground terminal. Less sensitive receivers and less powerful transmitters can be used on the ground than are needed for passive satellites. Also called active comsat. active component- 1. Those components in a circuit that have gain, or direct current flow, such as SCRs, transistors, thyristors, or tunnel diodes. They change the basic character of an applied electrical signal by rectification, amplification, switching, and so forth. (Passive elements like inductors, capacitors, and resistors have no gain characteristics.) 2. A device, the output of which is dependent on a source of power other than the main input signal. 3. A device capable of some dynamic function (such as amplification, oscillation, signal control) and which usually requires an external power supply for its operation. 4. Broadly, any device (including electromechanical relays) that can switch (or amplify) by application of low-level signals. active computer-The one of two or more computers in an installation that is online and processing data. active comsat -See active communications satellite. active current-In an alternating current, a component in phase with the voltage. The working component as distinguished from the idle or wattless component. active decoder-A device that is associated with a ground station and automatically indicates the radar beacon reply code that is received in terms of its number or letter designation. active delay line-A digital delay module that incorporates a passive delay line and a series of logical gate circuits. These modules are used specifically with digital or logic signals. Also called digital delay line, digital delay unit, digital delay module, and digital programmable delay line. active d e v i c e -See active component. active display-A display, such as a cathode-ray tube, electroluminescent display, or plasma panel, that presents information by emitting light. active ECM-See jamming. active electric network- An electric network containing one or more sources of energy. active element-1. The driven or self-excited element in a multielement antenna or antenna array. 2. Also known as the responsive element. That part of a detector on which the infrared energy is projected and which, when radiation falls on it, undergoes a physical change that results in an electrical signal. See active component.

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active equalizer- An equalizer designed to correct deficiencies in a speaker system’s response. Such equalizers, which are designed to precisely match specific speaker systems, usually connect between the amplifier and preamplifier, or in one of the amplifier’s tape-monitor circuits. active filter- 1. A device employing passive network elements and amplifiers. It is used for transmitting or rejecting signals in certain frequency ranges or for controlling the relative output of signals as a function of frequency. 2. A high-pass, low-pass, bandpass, or bandelimination filter that uses an active element, such as an operational amplifier, and relatively small capacitors, rather than the larger inductors and capacitors that would be required in a conventional passive filter. 3. A circuit whose gain depends on the frequency of the input signal. 4. A filter, consisting of an amplifier and suitable tuning elements, usually inserted in a feedback path. 5 . A filter that uses active devices such as operational amplifiers to synthesize the filter response function. This technique has an advantage at high speeds because the need for inductors (with their poor high-frequency characteristics) is eliminated. active guidance -See active homing. active homing -A system whereby a missile homes in on a target by means of a radar aboard the missile. Also called active guidance. active infrared detection -An infrared detection system in which a beam of infrared rays is transmitted toward one or more possible targets, and the rays reflected from the target are detected. active infrared system-A system in which the object is irradiated by a source of infrared energy, which, in turn, is reflected by the object onto a detector. A snooperscope is an active infrared system. active intrusion sensor- An active sensor that detects the presence of an intruder within the range of the sensor. Examples are an ultrasonic motion detector, a radio-frequency motion detector, and a photoelectric alarm system. See also passive intrusion sensor. active jamming- 1. Intentional radiation or reradiation of electromagnetic waves to impair the use of a specific portion of the electromagnetic-wave spectrum. 2. Transmission or retransmission of signals for the express purpose of disrupting communications. active junction-In a semiconductor, a change in ntype to p-type doping, or vice versa, by a diffusion step. On discrete transistors there are two active junctions, the collector-base junction and the emitter-base junction. a c t i v e leg -Within a transducer, an electrical element that changes its electrical characteristics as a function of the applied stimulus. active line-In a US. television picture, one of the lines (approximately 488) that make up the picture. The remaining 37 of the 525 available lines are blanked; they are called inactive lines. active maintenance downtime -The time during which work is actually being done on an item, from the recognition of an occurrence of failure to the time of restoration to normal operation. This includes both preventive and corrective maintenance. active material-1. In the plates of a storage battery, lead oxide or some other active substance that reacts chemically to produce electrical energy. 2. The fluorescent material, such as calcium tungstate, used on the screen of a cathode-ray tube. active matrix-A display matrix with a transistor at each pixel location to individually store its state (on or off). Pixels in active matrix panels only need to be addressed when they are being turned on or off.

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active mixer and modulator-A device requiring a source of electrical power and using nonlinear network elements to heterodyne or combine two or more electrical signals. active network- 1. A network containing passive and active (gain) elements. 2. An electrical network that includes a source of energy. active pressure-In an ac circuit, the pressure that produces a current, as distinguished from the voltage impressed on the circuit. active p r o b e -A test probe, generally used with an oscilloscope, that is so named because of the active components used within probe circuitry. These components consist of one or all of the following: transistors, diodes, integrated circuits, or FETs. If FETs are used, these probes are often referred to as FET probes. active pull-up-An arrangement in which a transistor is used to replace the pull-up resistor in an integrated circuit in order to provide low output impedance without high povver consumption. active RC network-A network formed by resistors, capacitors, and active elements. active redundancy-That redundancy wherein all redundant items are operating simultaneously rather than being switched on when needed. active repair time-That portion of corrective maintenance downtime during which repair work is being done on the item, including preparation, fault location, part replacement, adjustment and recalibration, and final test time. It may also include part procurement time under shipboard or field conditions. activle satellite-A satellite that receives, regenerates, and retransmits signals between stations. See also communications satellite. activlesensor -A sensor that detects the disturbance of a radiation field that is generated by the sensor. See also passive sensor. ctive sonar-See sonar. ctive splitter-See line splitter. active substrate-1. A substrate in which active elements, axe formed to provide discrete or integrated devices. Examples of active substrates are single crystals of semiconductor materials within which are transistors, resistors, and diodes, or combinations of these elements. Another example is ferrite substrates within which electromagnetic fields are used to perform logical, gating, or memory functions. 2. A substrate for an integrated component in which parts display transistance. 3. A working part of the electronic circuit, which it supports physically. 4. In an integrated circuit, a substrate consisting of singlecrystal semiconductor material into which the various IC components are formed; it acts as some or all of the components. This is in contrast to a substrate consisting of a dielectric, on whose surface the various components are deposited. active swept-frequency interferometer radar--A dual radar system for air surveillance. It provides angle and range information of high precision for ting target locations by trigonometric techniques. ive systems-In radio and radar, systems that require transmitting equipment, such as a beacon or transponder, to be carried in the vehicle. active tracking system-Usually, a system that requires the addition of a transponder or responder on board the vehicle to repeat or retransmit information to the tracking equipment; e.g., dovap, secor, azusa. active transducer-1. A type of transducer in which its output waves depend on one or more sources of power, apart from the actuating waves. 2. A transducer that requires energy from local sources in addition to that which is received.

active mixer and modulator - adaptive control active trim-Trimming of a circuit element (usually resistors) in a circuit that is electrically activated and operating to obtain a specified functional output for the circuit. See functional trimming. active wire-The wire of an armature winding that produces useful voltage. That portion of the winding in which induction takes place. activity- 1. In a piezoelectric crystal, the magnitude of oscillation relative to the exciting voltage. 2. The intensity of a radioactive source. 3. Operations that result in the use or modification of the information in a computer file. activity curve-A graph showing how the activity of a radioactive source varies with time. activity ratio-The ratio of the number of records in a computer file that have activity to the total number of records in the file. ac transducer-A transducer that, for proper operation, must be excited with alternating currents only. Also a device, the output of which appears in the form of an alternating current. actual height-The highest altitude at which refraction of radio waves actually occurs. actual power-The average of values of instantaneous power taken over one cycle. actuating device-A mechanical or electrical device, either manual or automatic, that operates electrical contacts to bring about signal transmission. actuating system- I. In a device or vehicle, a system that supplies and transmits energy for the operation of a mechanism or other device. 2. A manually or automatically operated mechanical or electrical device that operates electrical contacts to effect signal transmission. actuating time-The time at which a specified contact functions. actuator- 1. In a servo system, the device that moves the load. 2. The part of a relay that converts electrical energy into mechanical motion. 3. Switch part to which an external force is applied to operate the switch. 4. A manual or automatic switch or sensor, such as a holdup button, magnetic switch, or thermostat, that causes a system to transmit an alarm signal when manually activated or when the device automatically senses an intruder or other unwanted condition. 5 . A motorized arm that moves a satellite dish into position under the control of a receiver. ACU -Abbreviation for automatic calling unit. ac voltage -See alternating voltage. acyclic m a c h i n e -A direct-current machine in which the voltage generated in the active conductors maintains the same direction with respect to those conductors at all times. ald -Abbreviation for analog-to-digital. Also a-d, A-D, or AD. adapter-1. A fitting designed to change the terminal arrangement of a jack, plug, socket, or other receptacle, so that other than the original electrical connections are possible. 2. An intermediate device that permits attachment of special accessories or provides special means for mounting. 3. A device for connecting two parts of an apparatus that would not be directly connectable because of incompatible dimensions, terminations, currents, voltages, frequencies, etc. adaptive communication-A method in which automatic changes in the communications system allow for changing inputs or changing characteristics of the device or process being controlled. Also called selfadjusting communication or self-optiwizing comunication. adaptive control-1. A control method that uses sensors for real-time measurement of process variables

adaptive control system - address constant with calculation and adjustment of control parameters as a method of achieving near-optimum process performance. 2. A method of control in which actions are continuously adjusted in response to feedback. adaptive control s y s t e m -A device whose parameters are automatically adjusted to compensate for changes in the dynamics of the process to be controlled. An AFC circuit utilizing temperature-compensating capacitors to correct for temperature changes is an example. a d a p t i v e telemetry -Telemetry having the ability to select certain vital information or any change in a given signal. adaptor-A device that locates and supports products to be tested. Generally, it is made of an insulating material with locator pins mounted to precisely position the product to a spring contact probe test pattern. Also, an adaptor serves as an intermediate between the circuit verifier and the interchangeable test head that contains the test pattern. adc -Abbreviation for analog-to-digital converter. Also ADC. A d c o c k antenna-A pair of vertical antennas separated by one-half wavelength or less and connected in phase opposition to produce a figure-8 directional pattern. A d c o c k direction finder -A radio direction finder using one or more pairs of Adcock antennas for directional reception of vertically polarized radio waves. type of radio range A d c o c k radio range-A utilizing four vertical antennas (Adcock antennas) placed at the comers of a square, with a fifth antenna in the center. a/d converter-Abbreviation for analog-to-digital converter. Also a-d, A-D, or A/D converter. 1. A unit or device that converts an analog signal, that is, a signal in the form of a continuously variable voltage or current, to a digital signal. 2. A circuit that accepts information in a continuously varying ac or dc current or voltage and whose output is the same information in digital form. 3. A circuit or device for producing a set of digital output signals representing the magnitude of a voltage applied to its input. add-and-subtract relay-A stepping relay capable of being operated so as to rotate the movable contact arm in either direction. addend-A quantity that, when added to another quantity (called the augend), produces a result called the sum. adder - 1. A device that forms the sum of two or more numbers or quantities impressed on it. 2. In a color TV receiver, a circuit that amplifies the receiver primary signal coming from the matrix. Usually there is one adder circuit for each receiver primary channel. 3. An arrangement of logic gates that adds two binary digits and produces sum and carry outputs. add-in -Components (expansion boards, cartridges, or chips) that can increase a computer’s capabilities, such as memory, graphics, and communications. Add-ins usually refer to an entire circuit board. See also add-on. add-in memory- Additional computer memory that is added to a computer system within the computer’s physical housing. Typically the add-in memory is inserted, in board form, into an available card slot on the assembly, the connections for which have already been placed on the existing computer. Additional memory may be in the form of semiconductor RAM, CCD, bubble memory, disk, or tape. additional station -Any amateur radio station licensed to an amateur radio operator, normally for a specific land location other than the primary station. addition record-A new record created during the processing of a file in a computer.

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additive -Sometimes referred to as the key. A number, series of numbers, or alphabetical intervals added to a code to put it in a cipher. additive color-A system that combines two colored lights to form a third. additive primaries-Primary colors that can be mixed to form other colors, but which cannot themselves be produced by mixing other primaries. Red, green, and blue are the primaries in television because, when added in various proportions, they produce a wide range of other colors. additive process -A printed-circuit manufacturing process in which a conductive pattern is formed on an insulating base by electrolytic chemical deposition. additive synthesis- A technique for creating musical notes whereby sine waves are added together to create new waveforms. Frequently used in electric organs rather than in synthesizers. additron -An electrostatically focused, beamswitching tube used as a binary adder in high-speed digital computers. (No longer used.) add mode -Allows entry of numbers in a calculator to two decimal places without the need to enter the decimal point. add-on -Circuitry or system that can be attached to a computer to increase memory or performance. See also add-in. add-on component or add-on device-A discrete or integrated prepackaged or chip component that is attached to a film circuit to complete the circuit functions. add-on memory -Additional computer memory that is added externally and is plug compatible with the computer system. The add-on memory is connected with an external connector cable to the computer, where provision has been made for memory expansion. Such a memory device is also available in its own housing, in which case it is physically placed beside the computer’s main cabinet. Additional memory may be in the form of semiconductor RAM, CCD, bubble memory, disk, or tape. address - 1. An expression, usually numerical, that designates a specific location in a storage or memory device or other source or destination of information in a computer. 2. An identification, as represented by a name, label, or number, for a register, location in storage, or any other data source or destination, such as the location of a station in a communications network. 3. Loosely, any part of an instruction that specifies the location of an operand for the instruction. 4. To select the location of a stored information set for access. 5. In computer technology, a number used by the central processing unit (CPU) to specify a location in memory. 6. Element(s) of a packet frame that identifies the source and/or destination stations by means of an agreed bit pattern. 7. A unique sequence of letters or numbers for the location of data or the identity of an intelligent device. address bus-1. A unidirectional bus over which digital information appears to identify either a particular memory location or a particular device. 2. The set of output pins from a microprocessor chip and the associated circuitry linking them to other devices for the purpose of addressing those chips or parts of them. See a h bus system. address c h a r a c t e r s -Blocks of alphanumeric characters that identify users or stations uniquely. address comparator-In a computer, a device that ensures that an address being read is the right one. address c o m p u t a t i o n -The process by which the address part of an instruction in a digital computer is produced or modified. address constant -See base address.

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addressed memory-In a computer, memory secitions containing each individual register. address field-The portion of an instruction that specifies the Location of a particular piece of information -in a Computer memory. addressing mode- An addressing method. One of several different addressing methods possible in micro]processors. address modification-In a computer, a change -in the address portion of an instruction or command :such that, if the routine which contains that instruction or command is repeated, the computer will go to a new address or location for data or instructions. address part- In an electronic computer instrucition, a portion of an expression designating location. See also instruction code. address-routing indicator-Group of characters tcontained in a message heading that designates the tdestinatiom of the message. add-subtract time-The time required by a digital computer to perform addition or subtraction. It does not -include tlhe time required to obtain the quantities from storage and put the result back into storage. add time-The time required in a digital computer it0 perform addition. It does not include the time required ito obtain the quantities from storage and put the result back into storage. aid encoder -Analog-to-digital encoder. A device ithat changes an analog quantity into an equivalent digital representation. Also referred to as an a-d, A-D, or (encoder. adf-See automatic direction finder. Also referred to as ADF. adiabatic damping -A reduction in the size of an accelerator beam as the energy of the beam is increased. adiabatic demagnetization -A technique used to obtain temperatures within thousandths of a degree of absolute :zero. It consists of applying a magnetic field to a substance at a low temperature and in good thermal (contact with its surroundings, insulating the substance ithermally, and then removing the magnetic field. A-display -Also called A-scan. A radarscope presentation in which time (distance or range) is one coordinate (usu.ally horizontal) and the target appears displaced ]perpendicularto the time base. a d j a o e n c y -In character recognition, a condition -in which the character-spacing reference lines of two (charactersprinted consecutively on the same line are less ithan a specified distance apart. adjaoent- and alternate-channel selectivity.A measure of the ability of a receiver to differentiate lbetween a desired signal and signals that differ in fretquency from the desired signal by the width of one chaninel or twlo channels, respectively. adjaclent audio (sound) c h a n n e l -The rf carrier :frequency that contains the sound modulation associated with the next-lower-frequency television channel. a d j a c e n t channe! -That frequency band immediately above or below the one being considered. adjaclent-channel attenuation -See selectance. adjaoent-channel interference-Undesired sig!rials received on one communication channel from a ibansmitter operating on a channel immediately above or Ibelow. adjacent-channel selectivity-The ability of a ireceiver to reject signals on channels adjacent to the (channelof the desired station. a d j a c ' e n t conductor -Any conductor next to another conductor, either in the same multiconductor cable layer or in adjacent layers.

addressed memory - advanced license a d j a c e n t sound channel -In television, the rf channel containing the sound signal modulation of the next lower channel. a d j a c e n t video carrier-The rf carrier that carries the picture modulation for the television channel immediately above the channel to which the viewer is tuned. a d j u s t a b l e component -Any circuit component whose electrical value may be varied at will, e.g., adjustable capacitor, inductor, resistor, or load. a d j u s t a b l e resistor- 1. A resistor that has the resistance wire partly exposed to enable the amount of resistance in use to be adjusted occasionally by the user. Adjustment requires the loosening of a screw, the subsequent moving of the lug, and retightening of the screw. 2. A fixed resistor with a movable contact (or tap) that can be positioned along the length of the resistive path.

Adjustable resistor. a d j u s t a b l e voltage divider --A wirewound resistor with one or more movable terminals that can be slid along the length of the exposed resistance wire until the desired voltage values are obtained. a d j u s t e d circuit -Also called bolted-fault level. In a circuit, the current measured under short-circuit conditions with the leads that are normally connected to the circuit breaker bolted together. a d j u s t e d decibels-An expression of the ratio of the noise level to a reference noise at any point in a transmission system, when the noise meter has been adjusted to allow for the interfering effect under specified conditions. admittance-1. The ease with which an alternating current flows in a circuit. The reciprocal of impedance; usually expressed in siemens. Symbol is Y or y . 2. The (sinusoidal) current in a circuit divided by the terminal voltage. 3. The vector sum of a resistive component of conductance and a reactive component of susceptance. ADP -Abbreviation for automatic data processing. ADSL -Abbreviation for Asymmetric Digital Subscriber Line. A video display terminal distribution video system delivering video over existing (i.e., copper) telephone lines. adsorption-The deposition of a thin layer of gas or vapor particles onto the surface of a solid. The process is known as chemisorption if the deposited material is bound to the surface by a simple chemical bond. ADU -Abbreviation for automatic dialing unit. advance ball -In mechanical recording, a rounded support (often sapphire) that is attached to a cutter and rides on the surface of the recording medium. Its purpose is to maintain a uniform mean depth of cut and to correct for small irregularities on the surface of the disc. advance calling -A telecommunications feature in which voice messages can be spoken into the telephone for automatic delivery at a prearranged time to my other telephone or telephones. a d v a n c e d license-A license issued by the FCC to amateur radio operators who are capable of sending

advance wire - agonic line and receiving Morse code at the rate of 13 words per minute and are familiar with general and intermediate radio theory and practice. Its privileges include exclusive use of certain frequencies. advance wire- An alloy of copper and nickel, used in the manufacture of electric heating units and some wirewound resistors. aeolight-A glow lamp that uses a cold cathode and a mixture of inert gases. Its illumination can be regulated with an applied signal voltage and it is often used as a modulation indicator for motion picture sound recording. aerial-See antenna. aerial cable-A cable installed on a pole line or similar overhead structure. aerodiscone antenna- An aircraft antenna that is aerodynamically shaped and is physically small compared with other antennas having similar electrical characteristics. Its radiation pattern is omnidirectional and linearly polarized. aerodrome control radio station -A radio station providing communications between an airport control tower and aircraft or mobile aeronautical radio stations. aerodynamics-The science of the motion of air and other gases. Also, the forces acting on bodies such as aircraft when they move through such gases, or when such gases move against or around the bodies. aeromagnetic-Pertaining to the magnetic field of the earth as surveyed from the air. aeronautical advisory station-A station used for civil defense and advisory communications with private aircraft stations. aeronautical broadcasting service-The broadcasting service intended for the transmission of information related to air navigation. aeronautical broadcast station -A station that broadcasts information regarding air navigation and mete orological data pertinent to aircraft operation. aeronautical fixed service-A fixed service intended for the transmission of information relating to air navigation and preparation for and safety of flight. aeronautical fixed station-A station operating in the aeronautical fixed service. aeronautical ground station -A radio station operated for the purpose of providing air-to-ground communications in connection with the operation of aircraft. aeronautical marker-beacon station-A land station operating in the aeronautical radionavigation service and providing a signal to designate a small area above the station. aeronautical mobile service- A radio service between aircraft and land stations or between aircraft stations. aeronautical radio-beacon station -An aeronautical radionavigation land station transmitting signals that are used by aircraft and other vehicles to determine their position bearing or position in relation to the aeronautical radio beacon station. aeronautical radionavigation sewice-A radionavigation service intended for use in the operation of aircraft. aeronautical radio service- 1. Service carried on between aircraft stations andor land stations. 2. Special radio for air navigation. 3. Service that includes aircraft-to-aircraft, aircraft-to-ground, and ground-toaircraft communications important to the operation of aircraft. aeronautical station-A land station (or in certain instances a shipboard station) in the aeronautical mobile service that carries on communications with aircraft stations.

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aeronautical telecommunication-Electronic and nonelectronic communications used in the aeronautical service. aeronautical telecommunication agency -An agency to which is assigned the responsibility for operating a station or stations in the aeronautical telecommunication service. aeronauticaltelecommunication log -A record of the activities of an aeronautical telecommunication station. aeronautical telecommunications-Any telegraph or telephone communications of signals, writing, images, and sounds of any nature by wire, radio, or other system or process of signaling, used in the aeronautical service. aeronautical telecommunication service-

Telecommunication service provided for aeronautical purposes. aeronautical telecommunication station-A station in the aeronautical telecommunication service. aeronautical utility land station -A land station located at an airport control tower and used for communications connected with the control of ground vehicles and aircraft on the ground. aeronautical utiiity mobile station -A mobile station used at an airport for communications with aeronautical utility land stations, ground vehicles, and aircraft on the ground. aerophare-See radio beacon. AES- Abbreviation for Audio Engineering Society. A professional group; the official association of technical personnel, scientists, engineers, and executives in the audio field. AF -See audio frequency. AFC -See automatic frequency control. afocal-An optical system with one set of object and image points at infinity. Literally, “without a focal length.” An afocal system receives its input image from infinity and projects its output image to infinity. AFSK- Abbreviation for audio-frequency shift keying. With this method of modulation, two tones (mark = 2125 Hz, space = 2295 Hz) are fed directly into the microphone jack of the transmitter. afterglow -Also called phosphorescence. 1. The light that remains in a gas-discharge tube after the voltage has been removed, or on the phosphorescent screen of a cathode-ray tube after the exciting electron beam has been removed. 2. The luminosity that remains in a rarefied gas after an electrodeless discharge has traversed the gas. afterpulse -In a photomultiplier, a spurious pulse induced by a preceding pulse. AGC-See automatic gain control. age-To maintain an electrical component in a specified environment, as with respect to pressure, temperature, applied voltage, etc., until its characteristics stabilize. aggregate function-A command that perfoms calculations based on a set of values rather than on a single value. agile receiver- A satellite receiver that can be tuned to any desired channel. aging- 1. Storing a permanent magnet, capacitor, semiconductor, meter, or other device, sometimes with voltage applied, until its desired characteristics become essentially constant. 2. The change of a component or a material with time under defined environmental conditions, leading to improvement or deterioration of properties. agonic line-An imaginary line on the earth‘s surface, all points of which have zero magnetic declination.

15 AGP -- Abbreviation for accelerated graphics port. AGREE- Advisory Group on Reliability of Electronics Equipment. I -See artificial intelligence. aided tracking-A system of tracking a target signal in bearing, elevation, or range (or any combination of these variables) in which manual correction of the tracking error automatically corrects the rate at which the tracking mechanism moves. AlEE -Abbreviation for American Institute of Electrical Engineers. Now merged with IRE to form IEEE. air bearing-A means of supporting magnetic tape on an ai^ film rather than by means of a sliding or rolling contact. Usually, an air bearing is a perforated cylinder; pressurized air flows through the perforations and forms a film that prevents the tape from contacting the cylinder. airboirne intercept radar- Short-range airborne radar employed by fighter and interceptor planes to track down their targets. airboirrae long-range input -Airborne equipment designed to extend air-surveillance coverage seaward so that long-range interceptors may be used. airborne moving-target indicator-A type of airborne-radar display that does not present essentially stationary objects. airboirne noise-Undesired sound in the form of fluctuatioas of air pressure about the atmospheric pressure as a mean. airborne radar platform -Airborne surveillance and height-finding radar for early warning and control. air capacitor-A capacitor in which air is the only dielectric material between its plates. aircarrier aircraft station -A radio station aboard an aircraft that is engaged in or essential to the transportation of passengers or cargo for hire. air cell-A primary cell in which depolarization at the positive electrode is accomplished chemically by reduction of the oxygen in the air. air column-The air space within a horn of an acoustic (chamber. air colndenser-See air capacitor. air-cooled tube- An electron tube in which the generated heat is dissipated to the surrounding air directly, through metal heat-radiating fins, or with the aid of channels or chimneys that increase the air flow. air-core cable-A telephone cable in which the interstices in the cable core are not filled with a moisture barrier. air-core coil-A number of turns of spiral wire in which no1 metal is used in the center. air-core transformer-A transformer (usually rf) having two or more coils wound around a nonmetallic core. Tr,msformers wound around a solid insulating substance or on an insulating coil form are included in this category. aircraft bonding -Electrically connecting together all the metal structure of the aircraft, including the engine and metal covering of the wiring. aircraft flutter-Flickering (repetitive fading and intensifying) in a TV picture as the signal is reflected from flying aircraft. The reflected signal arrives in or out of phase with the normal signal and thus strengthens or weakens the latter. aircraft station -A radio station installed on aircraft and continuously subject to human control. air d e f e n s e control center -Principal information, communications, and operations center from which all aircraft, antiaircraft operations, air-defense artillery, guided missiles, and air-raid warning functions of a

AGP - air-position indicator specific area of air defense responsibility are supervised and coordinated. air defense identification zone-Airspace of defined dimensions within which the ready identification, location, and control of aircraft is required. air dielectric capacitor-A capacitor with a dielectric consisting of air. airdrome control station-A station used for communication between an airport control tower and aircraft. air environment -In communications electronics, all airborne equipment that is part of the communicationselectronics system, as distinguished from the equipment on the ground, which belongs to the ground environment. air gap-1. A nonmagnetic discontinuity in a ferromagnetic circuit. For example, the space between the poles caf a magnet-although filled with brass, wood, or any other nonmagnetic material -is nevertheless called an air gap. This gap increases magnetic reluctance and prevents saturation of the core. 2. The air space between two magnetically or electrically related objects. air/ground control radio station -An aeronautical telecommunication station with the primary responsibility of handling communications related to the operation and control of aircraft in a given area. air/ground liaison code-Set of symbols for a limited number of words, phrases, and sentences used for communications between air and ground forces. air-motion transformer-A type of speaker in which the air is not pushed into vibration by a piston, but rather squeezed by the contractions of a folded diaphragm. air navigation radio aids -Aeronautical ground stations, radio beacons, direction finders, and similar facilities. airplane flutter rejection-The measure of a receiver’s immunity to the effects of wavering signals produced by aircraft in the reception path. airport beacon-A beacon (light or radio) to indicate the location of an airport. airport control station -A station that furnishes communications between an airport control tower and aircraft in the immediate vicinity; messages are Limited to those related to actual aviation needs. airport radar control-The surveillance-radar portion of radar approach control. airport runway beacon -A radio-range beacon that defines one or more approaches to an airport. airport s u r f a c e detection equipment -Abbreviated ASDE. 1. Radar that shows the movement of aircraft and other vehicles on the ground at an airport. Valuable tool at night and during low visibility. 2. A digital radar system used to track planes and vehicles on airport runways and up to 200 feet in altitude. Unlike previous surface radar systems, ASDE provides clear images in bad weather. airport surveillance r a d a r -1. Abbreviated ASR. A short-range radar system that maintains constant surveillance over aircraft at the lower levels of flight. Distinct from air route surveillance radar (ARSR), which is long-range radar- 150-mile (241-km) radius- to control traffic between terminals. 2. An air-traffic-control radar that scans the airspace 30 to 60 miles (48 to 98 km) around an airport and displays the location of a11 aircraft below a certain altitude and all obstructions near the control tower. air-position indicator -Airborne computing system that presents a continuous indication of aircraft position on the basis of aircraft heading, air speed, and elapsed time.

air-spaced coax

- aliasing

air-spaced coax-A coaxial cable in which air is basically the dielectric material. The conductor may be centered by means of a spirally wound synthetic filament, by beads, or by braided filaments. This construction is also referred to as an air dielectric. air surveillance-Systematic observation of airspace by electronic, visual, or other means, primarily to identify and determine the movements of aircraft and missiles, friendly and enemy, in the airspace under observation. airtime-Time spent on a cellular phone, which is usually billed to the subscriber on a per-minute basis. air-to-ground communication -Transmission of radio signals from an aircraft to stations or other locations on the earth’s surface, as differentiated from ground-toair, air-to-air, or ground-to-ground communications. air-to-ground radio frequency-The frequency or band of frequencies agreed upon for transmission from an aircraft to an aeronautical ground station. air-to-surface missile -A missile designed to be dropped from an aircraft. An internal homing device or the aircraft’s radio guides it to a surface target. airwaves-Slang expression for radio waves used in radio and television broadcasting. alacritized switch- 1. A mercury switch treated to yield a low adhesional force between the rolling surface and mercury pool, resulting in a decreased differential angle. 2. A mercury switch in which the tendency of the mercury to stick to the mating parts has been reduced. alarm-A device that signals the existence of an abnormal condition by means of an audible or visible discrete change, or both, intended to attract attention. An alarm circuit produces or transmits an alarm signal. alarm condition-A threatening condition, such as an intrusion, fire, or holdup, sensed by a detector. alarm device-A device that signals a warning in response to an alarm condition, such as a bell, siren, or annunciator. alarm discrimination-The ability of an alarm system to distinguish between those stimuli caused by an intrusion and those which are a part of the environment. alarm hold-A means of holding an alarm once sensed. The typical magnetic trap does not hold or latch, and thus the reclosing of a trapped door resets the typical magnetic trap. A hold circuit applied to such a device indicates that the door has been opened and continues to so indicate until reset. alarm line-A wired electrical circuit used for the transmission of alarm signals from the protected premises to a monitoring station. alarm relay-A relay, other than an annunciator, used to operate, or to operate in connection with, a visual or audible alarm. alarm state-The condition of a detector that causes a control unit in the secure mode to transmit an alarm signal. alarm system-An assembly of equipment and devices designated and arranged to signal the presence of an alarm condition requiring urgent attention, such as unauthorized entry, fire, temperature rise, etc. The system may sound a local warning or alert the police, a central station, or a proprietary service. albedo-The reflecting ability of an object. It is the ratio of the amount of light reflected compared with the amount received. ALC -Abbreviation for automatic level (volume) control. 1. A special compressor circuit included in some tape recorders for automatically maintaining the recording volume within the required limits regardless of changes in the volume of the sound. 2. A circuit that automatically maintains recording levels within permissible limits, so that, no matter how loud or soft the sound being recorded,

16 the signal on the tape will not get strong enough to overmodulate and distort or soft enough to be lost in noise. Also known as automatic volume control (AVC). Alexanderson alternator- An early mechanical generator used as a source of low-frequency power for transmission or induction heating. It is capable of generating frequencies as high as 200,000 hertz. Alexanderson antenna-A vlf antenna consisting of a horizontal wire connected to ground at equally spaced points by vertical wires with base-loading coils; the transmitter is coupled to an end coil. Alford antenna-A square loop antenna comprising four linear sides with their ends bent inward so that capacitive loading is provided to equalize the current around the loop. algebraic adder-In a computer, an adder that provides the algebraic rather than arithmetic sum of the entered quantities. algebraic logic-A calculator mode that permits all calculations to be done in the order in which they are written. algebraic sum-The sum of two or more quantities combined according to their signs. (Compare with arithmetic sum.) ALGOL - 1. An international problem language designed for the concise, efficient expression of arithmetic and logical processes and the control (iterative, etc.) of these processes. From algorithmic language. 2. A highlevel language that has a context-free structure. algorithm- 1. A set of rules or processes for solving a problem in a finite number of steps (for example, a full statement of an arithmetic procedure for finding the value of sin x with a stated precision). See also procedure. 2. A series of equations, some of which may state inequalities, that cause decisions to be made and the computational process to be altered based on these decisions. 3. A set of rules or directions for getting a specific output from a specific input. The distinguishing feature of an algorithm is that all vagueness must be eliminated; the rules must describe operations that are so simple and well defined they can be executed by a machine. Furthermore, an algorithm must always terminate after a finite number of steps. 4. An ordered sequence of mathematical steps that always produces the correct answer to a problem, though the solution may be more lengthy than necessary. 5. A set of well-defined procedures for the solution of a problem in a limited number of steps. Algorithms are implemented in a computer by a programmed sequence of instructions. algorithmically generated pattern -An array of digital data automatically generated by a predetennined software routine or program. algorithmic language -An arithmetic language by which a numerical procedure may be presented to a computer precisely and in a standard form. algorithmic pattern generation -Real-time generation of input test patterns during test execution according to specified procedures, formulas, or algorithms. Also refers to procedures or algorithms used in automatic-testgeneration software for specific fault sets. alias-An alternate label. For instance, a label and one or more aliases may be used to identify the same data element or point in a computer program. aliasing-1. The introduction of error into the Fourier analysis of a discrete sampling of continuous data when components with frequencies too great to be analyzed with the sampling interval being used contribute to the amplitudes of lower-frequency components. 2. A phenomenon arising as a result of the sampling process in which high-frequency components of the original analog signal (whether information or noise) appear as lower frequencies in the sampled signal. Aliasing occurs when the

aliasing noise - alkaline cell

17 sampling rate is less than twice the highest frequency existing in the original analog signal. 3. Undesirable distortion component that can arise in digital audio equipment when the input signal’s frequency exceeds onehalf of the digital circuitry’s sampling rate. 4. The m i s taking of some object or situation for another, especially because of the way data is examined. Examples: movies of propellers and wagon wheels that seem to turn backward, muisical notes that are wrongly analyzed by sequential measurement (for instance, thought to be an octave too low), and, especially, “jaggies.” 5. Undesirable stairstep distortions in computer-generated images caused by inproper sampling techniques. The most common effect is a jagged edge along object boundaries. aliasiing noise -A distortion component that will be created if a sampled signal bandwidth is effectively greater than one-half the sampling rate. align .- 1. To adjust the tuned circuits of a receiver or transmitter for maximum signal response. 2. To put into proper relative position, agreement, or coordination when placing parts of a photomask together or placing a photornask over an etched pattern in the oxide on a semiconductor wafer. 3. To adjust the tuning of a multistage device so that all stages are adjusted to the same frequency or so that they work together properly. aligned bundle-See coherent bundle. aligned-grid tube- A multigrid vacuum tube in which at leash two of the grids are aligned one behind the other to give such effects as beam formation and noise suppression. alignment -1. The process of adjusting components of a system for proper interrelationship. The term is applied especially to (a) the adjustment of tuned circuits in a receiver to obtain the desired frequency response and (b) the synchronization of components in a system. 2. In a tape recorder, the physical positioning of a tape head relative to the tape itself. Alignment in all respects must conform to rigid requirements in order for a recorder to function properly. 3. The accuracy or proper relative position ‘of an image on a photomask with respect to an existing image on a substrate, as in a photoresist coating, or etched1 in the oxide of an oxidized silicon wafer. 4. A technique in the fabrication process of semiconductors by which a series of six to eight masks are successively registered to build up the various layers of a monolithic device. Each mask pattern must be accurately referenced to or aligned to all preceding mask patterns. 5. The accuracy of coordination or relative position of images on a semiconductor oxide coating and on the photomask, or any other images placed in relation to those. alignment chart- Also called nomograph, nomogram, or abac. Chart or diagam consisting of two or more lines on ,which equations can be solved graphically. This is done by laying a straightedge on the two known values and reading the answer at the point where the straightedge intersects the scale for the value sought. alignment pin- 1. A pin in the center of the base of a tube. A, projecting rib on the pin ensures that the tube is correcfly insefied into its socket. 2. Any pin or device that will ensure the correct mating of two components designed to be connected. alignment protractor-An instrument that indicates error in a pickup’s lateral alignment. It fits on the center spindle of the turntable, and the pickup stylus fits into a small hole on the device. The correct indication is shown when the angle of lateral movement of the pickup head is at 90” to the tangent of the groove at any point, although minimal tracking error is expected with most pickup arms. alignment tool -A special screwdriver or socket wrench used for adjusting trimmer or padder capacitors

A

C

B

9

10

Alignment chart. or cores in tuning inductances. It is usually constructed partly or entirely of nonmagnetic material. See also neutralizing tool.

! x HEXAGONAL SMALL TIP

Alignment tools.

alive- 1. Electrically connected to a sonrce of potential difference, or electrically charged to have a potential different from that of the earth. 2. Energized. 3. Reverberant, as a room in which sound reflects and echoes. alive circuit-A circuit that is energized. alkali-A compound that forms hydroxyl ions when in aqueous solution. Also called a base. alkaline cell- 1. A primary cell, similar to the zinccarbon cell, in which the negative electrode is granular zinc mixed with a potassium hydroxide (alkaline) electrolyte; the positive electrode is a polarizer in electrical contact with the outer metal can of the cell. A porous separator divides the electrodes. This type of cell delivers a terminal potential of 1.5 volts and has a 50 percent to 100 percent higher capacity than does a 1.5-volt zinc-carbon cell. Also called an alkaline-manganese cell. 2. A primary dry cell that has a very low internal resistance and high CATHODE

MIX

COL LECTOR

Alkaline cell.

CAP

all-channel tuning

- alphabetic string

service capacity. It is characterized by a relatively flat discharge curve under load. all-channel tuning -Ability of a television set to receive all assigned channels, VHF and UHF, channels 2 through 83, as well as cable channels. all-diffused monolithic integrated circuit Also called compatible monolithic integrated circuit. A microcircuit consisting of a silicon substrate into which all the circuit parts (both active and passive elements) are fabricated by diffusion and related processes. Allen screw-A screw having a hexagonal hole or socket in its head. Often used as a setscrew. Allen w r e n c h -A straight or bent hexagonal rod used to turn an Allen screw. alligator clip-A spring-loaded metal clip with long, narrow meshing jaws similar to the jaws of an alligator; it is used for making temporary electrical connections, generally at the end of a test lead on interconnection wire.

SCAEW

Alligator clip.

allocate-In a computer, to assign storage locations to main routines and subroutines, thus fixing the absolute values of symbolic addresses. allocated channel-A channel assigned to a specific user. allocated f r e q u e n c y band-A segment of the radio-frequency spectrum established by a competent authority that designates the use that may be made of the frequencies contained therein. allocated-use circuit-1. A circuit in which one or more channels have been allocated for the exclusive use of one or more services by a proprietary service; may be a unilateral or joint circuit. 2. Communication link specifically assigned to user@) warranting such facilities. allocation technique-The method of providing a process access to a shared resource. allochromatic-Exhibiting photoelectric effects due to the inclusion of microscopic impurities or as a result of exposure to various types of radiation. allophone-A variation in the pronunciation of a phoneme. An allophone can be regarded as the sound that results when a phoneme is placed in its environment. allotter -In a telephone system, a distributor, associated with the finder control group relay assembly, that allots an idle linefinder in preparation for an additional Call. allotter relay-In a telephone system, a relay of the linefinder circuit, the functions of which are to preallot an idle linefinder to the next incoming call from the line and to guard relays. allowable deviation -The permissible difference between any range of conditions and a reference condition. alloy- 1. A composition of two or more elements, of which at least one is a metal. It may be a solid solution, a heterogeneous mixture, or a combination of both. 2. Method of making pn junctions by melting a metallic dopant so that it dissolves some of the semiconductor material and then hardens to produce a doped alloy. alloy deposition -The process of depositing an alloy on a substrate during manufacturing. alloy-diffused transistor -A transistor in which the base is diffused and the emitter is alloyed. The

18 collector is the semiconductor substrate into which alloying and diffusion are effected. alloyed contact-An ohmic contact formed by an alloy process. alloy junction-Also called fused junction. A junction produced by alloying one or more impurity metals to a semiconductor. A small button of impurity metal is placed at each desired location on the semiconductor wafer, heated to its melting point, and cooled rapidly. The impurity metal alloys with the semiconductor material to form a p or n region, depending on the impurity used. alloy-junction photocell -A photodiode in which an alloy junction is produced by alloying (mixing) an indium disc with a thin wafer of n-type germanium. alloy-junction transistor -Also called fusedjunction transistor. A semiconductor wafer of p- or n-type impurities fused, or alloyed, into opposite sides of the wafer to provide emitter and base junctions. The base region comprises the original semiconductor wafer. alloy process -A fabrication technique in which a small part of the semiconductor material is melted together with the desired metal and allowed to recrystallize. The alloy developed is usually intended to form a pn junction or an ohmic contact. alloy transistor-A transistor in which the emitter and collector junctions are both alloy junctions. all-pass filter-A network designed to produce a delay (phase shift) and an attenuation that is the same at all frequencies; a lumped-parameter delay line. Also called all-pass network. all-pass network-A network designed to introduce phase shift or delay but not appreciable attenuation at any frequency. all-relay central off ice- An automatic centraloffice dial switchboard in which relay circuits are used to make the line interconnections. all-wave antenna -A receiving antenna suitable for use over a wide range of frequencies. all-wave receiver -A receiver capable of receiving stations on all the commonly used wavelengths in shortwave bands as well as in the broadcast band. alnico-An alloy consisting mainly of aluminum, nickel, and cobalt plus iron. Various subscripts and combinations of letters are available. Material can be found both in cast and sintered form, including isotropic and anisotropic alloys. Capable of very high flux density and magnetic retentivity, the alloy is used in permanent magnets for speakers, magnetrons, etc. alpha- 1. Emitter-to-collector current gain of a transistor connected as a common-base amplifier. For a junction transistor, alpha is less than unity, or 1. Alpha is usually defined as the ratio of a small change in collector current to the corresponding change in emitter current, when the collector-base voltage is kept constant. 2. Brain wave signals whose frequency is approximately 8 to 12 Hz. The associated mental state is relaxation, heightened awareness, elation, and in some cases, dreamlike. alphabet-An ordered set of all the letters and associated marks used in a language, for example, the Morse code alphabet, the 128 characters of the U.S. ASCII alphabet. a l p h a b e t i c coding -A system of abbreviation used in preparing information for input into a computer. Information may then be reported in the form of letters and words as well as in numbers. alphabetic-numeric-Having to do with the alphabetic letters, numerical digits, and special characters used in electronic data processing work. a l p h a b e t i c string -A character string containing only letters and special characters.

alpha cutoff frequency

I. 9

alpha cutoff frequency -The frequency at which the current gain of a common-base transistor stage has decreased to 0.707 of its low-frequency value. Gives a rough indication of the useful frequency range of the device. alphameric (alphanumeric) -Generic term for alphabetic letters, numerical digits, and special characters that are machine processable. alphameric characters-1. A character set that rnixes alphabetic characters, numeric characters, and usually punctuation characters. The alphabetic characters may be uppercase and/or lowercase or even in Japanese or Arabic script. 2. Consisting of letters and numbers. Also called alphameric or alphanumeric. alphai?umeric- 1. A generic term for alphabetic letters, numerical digits, and special ASCII characters that can be processed by a computer. A character set containing any combination of the above, 2. Consisting of letters and numbers. 3. All letters in the alphabet, the numbers 0 through 9, and special characters -such as -, I', *, $, (), and #-that are machine processable. alphailaumeric code-In computer practice or in communications, a code in which the letters of the alphabet are represented by numbers. alphainumeric display -Device consisting of a 1.ypewriter-stylekeyboard and a display (CRT) screen on which text is viewed. alphainumeric keys-Keys on a data entry device that resemble those on a standard keyboard. Usually they are used to manually input or edit text for the display system, although they can also be used in a function key mode. a ~ ~ h a i ~ u m ereader r ~ c -An instrument that reads ;alphabetic, numeric, and special characters by means of ;a photosensor that measures the varying intensity of the characters reaected from a light source. alphanumeric readout--A type of digital readout that displays both letters and numerals. alpha particle-A small, electrically charged partiicle thrown off at very high velocity by many radioactive materials.,including uranium and radium. Identical to the .nucleus of a helium atom, it is made up of two neutrons and two protons. Its electrical charge is positive and is lequal in magnitude to twice that of an electron. alpha ray-A stream of fast-moving alpha particles that produce intense ionization in gases through which they pass, are easily absorbed by matter, and produce a glow on a fluorescent screen. The lowest-frequency radioactive emissions. system -A signaling system in which the code to be used is designated by alphabetic characters. a ~ ~ ~ a detectoir-A - ~ a ~ e device that detects and displays alpha-wave segments of brain wave output. Used ter or sensor.

+,

edium that may be

alteration switch --A manual switch on a computer console or a program-simulated switch that can be set on or of1 to control coded machine instructions. alternate channel -A channel located two chanabove or below the reference channel. l ~ e r ~ ~ a t e - c h a n ~interference el -Interference caused in one communication channel by a transmitter operating; in the channel after an adjacent channel. See also second-channel interference.

- alternating-currenttransmission

alternate facility-A communications-electronics facility that is established for the purpose of replacing or supplementing another facility or facilities under real or simulated emergency conditions. alternate frequency -The frequency assigned for use at a certain time, or for a certain purpose, to replace or supplement the frequency normally used. alternate mode-A means of displaying on an oscilloscope the output signals of two or more channels by switching the channels, in sequence, after each sweep. alternate route or routing-A secondary or backup communications path to be used if the normal (primary) routing is not possible. alternate voiceidata Operation -Modem operations coordinated by voice over the same line that accommodates transmission. The modem is patched out of the circuit to allow this. A special switch, called an exclusion key, converts the line from voice to data. alternating-charge characteristic-The function relating, under steady-state conditions, the instantaneous values of the alternating component of transferred charge to the corresponding instantaneous values of a specified periodic voltage applied to a nonlinear capacitor. alternating current-Abbreviated ac. 1. -A flow of electricity that reaches maximum in one direction, decreases to zero, then reverses itself and reaches maximum in the opposite direction. The cycle is repeated continuously. The number of such cycles per second is the frequency. The average value of voltage during any cycle is zero. 2. Any signal that varies with time. It usually means that the current actually changes polarity with time. The plot of current versus time usually is a sine wave that comprises a succession of instantaneous values, the greatest of which is the amplitude or peak value. The time taken by one complete cyclic repetition is the period, and the number of periods in one second is the frequency.

Alternating current.

alternating currenVdirect current--A term applied to electronic equipment indicating it is capable of operation from either an alternating-current or directcurrent primary power source. alternating-current erasing head-An erasing head used in magnetic recording, in which alternating current produces the magnetic field necessary for erasing. Alternating-current erasing is achieved by subjecting the medium to a number of cycles of a magnetic field of a decreasing magnitude. The medium is, therefore, essentially magnetically neutralized. alternating-currentgenerator-A rotary machine that generates alternating current when its rotor, which may be either the armature or the field, is rotated by an engine or a motor. Also called an alternator. alternating-currentpulse -An alternating-current wave of brief duration. alternating-currenttransmission -In television, that form of transmission in which a fixed setting of the controls makes any instantaneous value of signal correspond to the same value of brightness only for a short time.

alternating f l a s h e r

- ambience

alternating flasher -A control that provides voltage first to one load and then to another load. This cycle repeats normally at a fixed rate per minute. alternating quantity-A periodic quantity that has alternately positive and negative values, the average value of which is zero over a complete cycle. alternating voltage-Also called ac voltage. Voltage that is continually varying in value and reverses its direction at regular intervals, such as that generated by an alternator or developed across a resistance or impedance through which alternating current is flowing. alternation -One-half of a cycle-either when an alternating current goes positive and retums to zero, or when it goes negative and returns to zero. Two alternations make one cycle. The complete rise and fall of a current traveling in one direction, or one-half of an alternating-current cycle. alternator -A device for converting mechanical energy into electrical energy in the form of an alternating current. alternator transmitter -A radio transmitter that generates power by means of a radio-frequency alternator. altimeter- An instrument that indicates the altitude of an aircraft above a specific reference level, usually sea level or the ground below the aircraft. It may be similar to an aneroid barometer, which utilizes the change of atmospheric pressure with altitude, or it may be electronic. altimeter station -An airborne transmitter, the emissions from which are used to determine the altitude of an aircraft above the surface of the earth. altitude delay-The synchronization delay introduced between the time of transmission of the radar pulse and the start of the trace on the indicator. This is done to eliminate the altitude circle on the plan-position-indicator display. ALU-Abbreviation for arithmetic and logic unit. 1. A device that performs the basic mathematical operations such as addition, subtraction, multiplication, and division of numbers (usually binary) presented to its inputs and provides an output that is an appropriate function of the inputs. 2. The arithmetic and logic unit internal to the microprocessor chip. This register handles all arithmetic and logical operations carried out as part of a microprocessor instruction. 3. The part of a CPU that executes adds, subtracts, shifts, AND logic operations, OR logic operations, etc. 4. A complex array of gates that can be used to perform binary arithmetic, logic operations, shifts and rotates, and complementing. 5 . One of the three essential components of a microprocessor, the other two being data registers and control. The ALU performs addition and subtraction, logic operations, masking, and shifting (multiplication and division). alumina -1. A ceramic used for insulators in electron tubes or substrates in thin-film circuits. It can withstand continuously high temperatures and has a low dielectric loss over a wide frequency range. Aluminum oxide (ALzOs). 2. The substrate material on which are deposited thin conductive and resistive layers for thin-film microwave integrated circuits. aluminized-screen picture tube -A cathode-ray picture tube that has a thin layer of aluminum deposited on the back of its fluorescent surface to improve the brilliance of the image and also prevent ion-spot formation. aluminizing-The process of applying a film of aluminum to a surface, usually by evaporation in a vacuum. aluminum-electrolytic capacitor-A capacitor with two aluminum electrodes (the anode has the oxide film) separated by layers of absorbent paper saturated with the operating electrolyte. The aluminum-oxide film

20 or dielectric is repairable in the presence of an operating electrolyte. aluminum-steel conductor-A composite conductor made up of a combination of aluminum and steel wires. In the usual construction, the aluminum wires surround the steel. alumoweld-A thin coating of aluminum fused to a steel core. Used in line wire and cable messengers. AM -See amplitude modulation. amateur -Also called a ham. 1. A person licensed to operate radio transmitters as a hobby. Any amateur radio operator. 2. A nonprofessional, usually noncommercial, devotee of any technology (as a hobby). amateur band -Any one of several radio frequency bands assigned for noncommercial use by licensed radio amateurs. In the United States, there are twelve such bands between 1.80 MHz and 1.3 GHz. Assignments are made by the Federal Communications Commission. amateur c a l l letters-Call letters and numbers assigned to amateur stations by the licensing authority. Call-letter combinations consist of a letter prefix denoting the country in which the station is situated, plus a number designating the location within the country, and two or more letters identifying the particular station. Example: K2ABC (K or W = United States, 2 = New York, and ABC = identification of individual licensee issued alphabetically except for special circumstances). amateur extra license-A license issued by the FCC to amateur radio operators who are able to send and receive Morse code at the rate of 20 words per minute and who are familiar with general, intermediate, and advanced radio theory and practice. Its privileges include all authorized amateur rights and the exclusive rights to operate on certain frequencies. amateur radio -The practice of operating electronic communications equipment as a hobby in the amateur service. Also refers to the equipment used for this purpose. amateur radiocommunication -Noncommercial radiocommunication by or among radio stations solely with a personal aim and without pecuniary or business interest. amateur radio license-The instrument of authorization issued by the Federal Communications Commission, comprised of a station license and, in the case of the primary station, incorporating an operator license. amateur radio operation -Radiocommunication conducted by an amateur radio operator from an amateur radio station. amateur radio operator- 1. A person interested in radio technique solely with a personal aim and without pecuniary interest, and holding a valid Federal Communications Commission license to operate amateur radio stations. 2. A private citizen who operates electronic communications equipment as a hobby. amateur radio service-A radiocommunication service of self-training, intercommunication, and technical investigation carried on by amateur radio operators. amateur service- A radiocommunication service that licensed operators with no pecuniary interest use for self-training, communication, and technical investigations. amateur station -A radio transmitting station operated by one or more licensed amateur operators. amateur-station call letters-See amateur call letters. ambience -1. Reverberant or reflected sound that reaches a listener’s ear from all directions as sound waves “bounce” successively off the various surfaces of a listening area-the walls, ceiling, etc. The term is usually reserved for large areas such as auditoriums and

21 concert halls, though home listening-rooms have their own ambience effects. 2. The indirect sounds heard in a concert hall or other large listening area that contribute to the overall auditory effect obtained when listening to live per€ormances. ambient -Surrounding. The surrounding environment calming into contact with the system or component in question. See also ambient noise; ambient temperature. ambient level -The level of interference emanating from sources other than the test sample, such as inherent noise of the measuring device and extraneous radiated fields. ambient light-Normal room light. Light existing in a room or other location that is characteristic of the environment. a ~ b ~ e n t - l i gfilter-A ~t filter used in front of a television picture-tube screen to reduce the amount of ambient light reaching the screen and to minimize the reflections of light from the glass face of the tube. ambiient lighting -Lighting designed to provide a substantially uniform level of illumination throughout an area, exclusive of any provision for special local requirements. arnbiient noise-1. Acoustic noise in a room or other location. Usually measured with a soundlevel meter. The term room noise commonly designates ambient noise at a telephone station. 2. Unwanted background noise picked up by a microphone, that is, any extraneous clatter in a room. Also any acoustic coloration that influences sounds. brought about by the acoustic properties of a room in which a recording is being made or replayed. 3. Interference present (in a communication line) at ;dl times. 4.Background electrical noise in electrical measurements and operation. perating temperature -The temperature of the air surrounding an object, neglecting small localized variations. ambient pressure -The general surrounding atmospheric pressure. ambient temperature- 1. Temperature of air or liquid surrounding any electrical part or device. Usually refers to the effect of such temperature in aiding or retarding removal of heat by radiation and convection from the part or device in question. 2. The prevailing temperature in the immediate vicinity of an object; the temperature of its environment. 3. A temperature within a given volume, e.g., a room or building. ambient temperature range-The range of environmental temperatures in the vicinity of a component or device over which it may be operated safely and within specifications, For forced-air cooled operation, the ambient temperature is measured at the air intake. ~ ~ b i '1. ~ An undesirable ~ i ~ -tendency of a synchro or servo system to seek a false null position in addition to the propler nuU position. 2. Inherent error resulting from multiple-.bit changes in a polystropic code. (Proper logic design prevents such errors.) ~ ~ ~ i count~ u Q A count u ~ on an electronic scaler that is obviously impossible. a r n b i reproduction ~ ~ ~ ~ ~ -The recreation of the ambience of an original recording situation with associated directionality. Sound from every direction is picked up by a tetrahedral microphone m a y and is then encoded onto two channels, which, upon decoding, produce sound through several speakers in a continuous range of directions around the listener, thus approximating the original. It can be subdivided into periphonic and pantophonic systems, the former concerning a complete sphere of information, the latter relating to a horizontal circle. Pantophonic reproduction does not distinguish vertical directionality, but still achieves remarkable realism.

AM broadcast channel -Any of the 1O-kHz wide bands of radio frequencies, which extend from 530 to 1710 kHz and are used for standard amplitude-modulated radio broadcasts. American Institute of Electrical Engineers (AIEE) -Now merged with IRE to iorm the IEEE. American Morse code-A system of dot-anddash signals originated by Samuel F. B. Morse and stili used to a limited extent for wire telegraphy in North America. It differs from the international Morse code used in radiotelegraph transmission. American National Standards Institute, inc. Abbreviated ANSI. An independent, industry-wide association that establishes standards €or the purpose of promoting consistency and interchangeability among the products of different manufacturers. Fonnerly United States of America Standards Institute (USASI) and American Standards Association (ASA). American Radio Relay League (ARRL organization of amateur radio operators. American Standards Association -Abbreviated ASA. See American National Standards Institute, Pnc. American wire gage (AWG) -The standard system used for designating wire diameter. Gage sizes range from No. 40, the smallest diameter wire, to No. 4/0, the largest. AWG sizes are used for specifying both solid and stranded wire. Gage numbers have an inverse relationship to size, i.e., larger numbers have smaller diameter.

American wire gage (AWG)

AWG

Diameter (mm)

AWG

(mm)

1 2 3 4 5 6 7 8 9 i0 11 12 13 14 15 16 17 18 19 20

7.35 6.54 5.83 5.19 4.62 4.12 3.67 3.26 2.91 2.59 2.31 2.05 1.83 1.63 1.45 1.29 1.15 1.02 0.912 0.812

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

0.723 0.644 0.573 0.511 0.455 0.405 0.361 0.321 0.286 0.255 0.227 0.202 0.180 0.160 0.143 0.127 0.113 0.101 0.090 0.C80

Diameter

AMIFM receiver-A device capable of converting either amplitude- or frequency-modulated signals into audio frequencies. AMIFM tuner-A device capable of converting either amplitude- or frequency-modulated signals into low-level audio frequencies. AML -Abbreviation for automatic modulation limiting. A circuit that uses an agc (automatic gain control) effect to prevent overmodulation. As a stronger voice signal is applied, this stage reduces the gain of the

ammeter - amplifier

22

audio amplifier(s), keeping the modulation level below 100 percent. ammeter -An instrument for measuring either direct or alternating electric current. Its scale is usually graduated in amperes, milliamperes, microamperes, or kiloamperes. ammeter s h u n t -A low-resistance conductor placed in parallel with the meter movement so that most of the current flows through this conductor and only a small part passes through the movement itself. This arrangement extends the usable range of the meter.

Iv/ SHUNT

Ammeter shunt.

ampere-hour meter- An electrical meter that measures and registers the amount or the integral, with respect to time, of the current that passes through it and is consumed in the circuit. Ampere’s rule-Current in a certain direction is equivalent to the motion of positive charges in that direction. The magnetic flux generated by a current in a wire encircles the current in the counterclockwise direction when the current is approaching the observer. ampere-turn -A measure of magnetomotive force, especially as developed by an electric current, defined as the magnetomotive force developed by a coil of one turn through which a current of 1 ampere flows; that is, 1.26 gilberts. a m p - h r -Abbreviation for ampere-hour or amperehours. amplidyne -A special direct-current generator used extensively in servo systems as a power amplifier. The response of its output voltage to changes in field excitation is very rapid, and its amplification factor is high. COMPENSATING FIELD

amorphous-A characteristic, particularly of a crystal,determining that it has no regular structure.

amorphous silicon-A noncrystalline form of silicon used to fabricate transistors on large-area flat displays. Although it is not as good a semiconductor as crystalline silicon, amorphous silicon is much easier to lay down. a m o r p h o u s silicon cell -A photovoltaic cell made of silicon and hydrogen atoms deposited in an irregular atomic structure on substrate. amortisseur winding -See damper winding. amp -Abbreviation for ampere. ampacity-The maximum current an insulated wire or cable can safely carry without exceeding either the insulation or jacket material limitations. Expressed in amperes. See nlso current-carrying capacity. amperage-The number of amperes flowing in an electrical conductor or circuit. ampere-Letter symbol: A. 1. A unit of electrical current or rate of flow of electrons. One volt across 1 ohm of resistance causes a current flow of 1 ampere. A flow of 1 coulomb per second equals 1 ampere. An unvarying current is passed through a solution of silver nitrate of standard concentration at a fixed temperature. A current that deposits silver at the rate of 0.001118 gram per second is equal to 1 ampere, or 6.25 x loJ8 electrons per second passing a given point in a circuit. 2. The constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular sections, and placed 1 meter apart in a vacuum will produce between these conductors a force equal to 2 x newtons per meter of length. ampere-hour-A current of 1 ampere flowing for 1 hour. Multiplying the current in amperes by the time of flow in hours gives the total number of amperehours. Used mostly to indicate the amount of energy a storage battery can deliver before it needs recharging, or the energy a primary battery can deliver before it needs replacing. One ampere-hour equals 3600 coulombs. a m p e r e - h o u r capacity-The amount of current a battery can deliver in a specified length of time under specified conditions. For example, a 100-ampere-hour battery can supply 20 amperes for 5 hours. ampere-hour efficiency -The number of amperehours obtained from a storage battery divided by the number of ampere-hours required to recharge the storage battery to its original condition.

CONTROL OUTPUT

Amplidyne.

amplification -1. Increase in size of a medium in its transmission from one point to another. May be expressed as a ratio or, by extension of the term, in decibels. 2. An increase in the magnitude of a signal brought about by passing through an amplifier. amplification f a c t o r (A) - 1. In a vacuum tube, the ratio of a small change in plate voltage to a small change in grid voltage required to produce the same change in plate current (all other electrode voltages and currents being held constant). 2. In any device, the ratio of output magnitude to input magnitude. amplified AGC -An automatic gain-control (AGC) circuit in which the control voltage is amplified before being applied to the tube or transistor, the gain of which is to be controlled in accordance with the strength of the incoming signal. amplified b a c k bias -Degenerative voltage developed across a fast time-constant circuit within a stage of an amplifier and fed back into a preceding stage. amplifier-1. A device that draws power from a source other than the input signal and that produces as an output an enlarged reproduction of the essential features of its input. The amplifying element may be an electron tube, transistor, magnetic circuit, or any of various devices. 2. A device for increasing the magnitude of a signal by means of a varying control voltage, maintaining the signal’s characteristic form as closely as possible to the original. 3. An electronic device for magnifying (and usually controlling) electrical signals. High-fidelity amplifiers consist of a preamplifier equalizer section, plus a power or basic amplifier section. In an integrated amplifier, both sections are built on one chassis and made available as a single unit. Alternately, the two sections are available as separate units. 4.Device for increasing power associated with a signal (voltage or

23 current). Basic types include dc, ac, audio, linear, radio, video, differential, pulse, logarithmic. amplifier noise -All spurious or unwanted signals, random or otherwise, that can be observed in a completely isolated amplifier in the absence of a genuine input signal. amplifier nonlinearity- 1. The inability of an amplifier to produce an output at all times proportionate to its input. 2. Gain deviation from a straight l i e on a plot of amplifier output versus input (the transfer curve). amplify -To increase in magnitude or strength, usually said of a current or voltage. amplifying delay Fine-A delay line used in pulse-compression systems to amplify delayed superhighfrequency signals. amplistat-A self-saturating type of magnetic amplifier. Amplitron -(Raytheon) A broadband crossed-field amplifier with a reentrant electron stream. The electron stream interacts with the backward wave of a nonreentrant rf structure. amplitude- 1. The magnitude of variation in a changing quantity from its zero value. The word must be modified with an adjective such as peak, rms, maximum, etc., which designates the specific amplitude in question. 2. The level of an audio or other signal in voltage or current terms. 3. The extent to which an alternating or pulsating current or voltage swings from zero or from a mean value. ampliitude-controlled rectifier -A rectifier circuit in which a thyratron is the rectifying element. amplitude density distribution-A function that gives the fraction of time that a voltage is within a narrow range. ~ ~ ~ l distortion ~ ~ u --Distortion d e that is present in an amplifier when the amplitude of the output signal fails to follow exactly any increase or decrease in the amplitudie of the input signal. It results from nonlinearity of the transfer function and gives rise to harmonic and intermodulation distortion. No amplifier is completely free from the effect because its transfer function is slightly curved. The nature of tlie curvature determines the order of the distortion produced, but negative feedback and other circuit configurations help minimize the curvature within the dynamic range and hence keep the distortion at a very low level. amplitude distribution function -A function that gives the fraction of time that a time-varying voltage is below a given level, amplitude fading -Fading in which the amplitudes of all frequency components of a modulated carrier wave are uniformly attenuated. ~ ~ p l i t ~ d ~ - f r e distortion ~ u e n c -The ~ distortion that occurs when the various frequency components ,of a cornplex wave are not amplified, attenuated, or transmitted equally well. amplitude-frequency response -The variation of gain, loss, amplification, or attenuation of a device or :system as a function of frequency. Usually measured in ithe region where the transfer characteristic is essentially linear. amplitude gate -See slicer. amplitude-level selection-The choice of the voltage level at which an oscilloscope sweep is triggered. amplitude limiter-A circuit or stage that automatiically recEuces the amplification to prevent signal peaks from exceeding a predetermined level. ~ ~ ~ l ~ ~ u d e - m o d utransmitter lated -A transmitter in which the amplitude of its radio-frequency wave i.s varied at a low frequency rate-usually in the audio or video range. This low frequency is the intelligence r:infomation) to be conveyed.

amplifier noise

- a ~ ~ l i t u dofenoise

ASSIGNED RF CARRIER RADIO FREOUENCY WITH AF OF STATION SUPERIMPOSED

AUDIO FRMUENCY

Ltb

Amplitude-modulated transmitter.

amplitude-modulated wave -A constant-frequency waveform in which the amplitude varies in step with the frequency of an impressed signal. amplitude modulation -Abbreviated AM. 1. Modulation in which the amplitude of a wave is the characteristic subject to variation. Those systems of modulation in which each component frequency ( f ) of the transmitted intelligence produces a pair of sideband frequencies at carrier frequency plus f and carrier frequency minus f.In special cases, the carrier may be suppressed; either the lower or upper sets of sideband frequencies may be suppressed; the lower set of sideband frequencies may be produced by one or more channels of information. The carrier may be transmitted without intelligence-canying sideband frequencies. The resulting emission bandwidth is proportional to the highest frequency component of the intelligence transmitted. 2. A process in which the program information is imposed on a carrier signal of constant frequency by varying its amplitude in proportion to program level. Used on the standard broadcast band (530 to 1710 kHz) and on long-wave and shortwave bands.

AUDIO MODULATING SIGNAL

E. = E.12 FOR 50% MODULATION

~

-

CARRIER

MODULATED WAVE

Amplitude modulation.

amplitude-modulation noise level -Undesired amplitude variations of a constant radio-frequency signal, especially in the absence of any intended modulation. amplitude noise-The effect on radar accuracy of the fluctuations in amplitude of the signal returned by the target. These fluctuations are caused by any change in aspect if the target is not a point source. amplitude of noise-When impulse-type noise is of random occurrence and so closely spaced that the individual waveshapes are not separated by the receiving equipment, then the noise has the waveshape and characteristics of random noise. Random-noise amplitude is proportional to the square root of the bandwidth. If the impulses are separated, the noise no longer has the

amplitude permeability

- analog network

waveshape of random noise and its amplitude is directly proportional to the bandwidth of the transmission system. amplitude permeability -The relative permeability at a stated value of field strength and understated conditions, the field strength varying periodically with time and no direct magnetic-field component being present. amplitude range -The ratio, usually expressed in decibels, between the upper and lower limits of program amplitudes that contain all significant energy contributions. amplitude resonance -The condition that exists when any change in the period or frequency of the periodic agency (but not its amplitude) decreases the amplitude of the oscillation or vibration of the system. amplitude response-The maximum output amplitude that can be obtained at various points over the frequency range of an instrument operated under rated conditions. amplitude selection -The process of selecting that portion of a waveform which lies above or below a given value or between two given values. amplitude separator -A television-receiver circuit that separates the control impulses from the video signal. amplitude-shift keying -Abbreviated ask. The modulation of digital information on a carrier by changing the amplitude of the carrier. amplitude-suppression ratio -In frequency modulation, the ratio of the magnitude of the undesired output to the magnitude of the desired output of an FM receiver when the applied signal is simultaneously amplitude and frequency modulated. Generally measured with an applied signal that is amplitude modulated 30 percent at a 400hertz rate and is frequency modulated 30 percent of the maximum system deviation at a 1000-hertz rate. amplitude versus f r e q u e n c y distortion-Distortion caused by the nonuniform attenuation or gain of the system, with respect to frequency under specified terminal conditions. AM rejection ratio-The ratio of the recovered audio output produced by a desired FM signal with specified modulation, amplitude, and frequency to that produced by an AM signal, on the same carrier, with specified modulation index. AM suppression-The ability of an FM tuner to reject AM signals. Expressed in decibels, it is the ratio between the tuner output with a 100-percent modulation FM signal to its output with a 30-percent modulated AM signal. AM tuner- A device capable of converting amplitudemodulated signals into low-level audio frequencies. amu -Abbreviation for atomic mass unit. analog -1. In electronic computers, a physical system in which the performance of measurements yields information concerning a class of mathematical problems. 2. Of or pertaining to the general class of devices or circuits in which the output varies as a continuous function of the input. 3. The representation of numerical quantities by means of physical variables, e.g., translation, rotation, voltage, resistance; contrasted with digital. 4. A continuous representation of phenomena in terms of points along a scale, each point merging imperceptibly into the next. An analog voltage, for example, may take any value. Realworld phenomena, such as heat and pressure, are analog (compare with digital). analog adder-An analog circuit or device that receives two or more inputs and delivers an output that is equal to their sum. analog amplifier-A device whose output is continuously proportional to the input stimulus.

24

analog channel-A computer channel in which the transmitted information can have any value between the defined limits of the channel. analog circuit-A circuit in which the output varies as a continuous function of the input, as contrasted with digital circuits. analog communications -A system of telecommunications employing a nominally continuous electrical signal that varies in frequency, amplitude, etc., in some direct correlation to nonelectrical information (sound, light, etc.) impressed on a transducer. analog computer- 1. A computer operating on the principle of creating a physical (often electrical) analogy of the mathematical problem to be solved. Variables such as temperature, light, pressure, distance, angle, shaft speed, or flow are represented by the magnitude of a physical phenomenon such as voltage or current. The computer manipulates these variables in accordance with the mathematical formulas “analogued” on it. 2. A computer system in which both the input and output are continuously varying signals. 3. A computing machine that works on the principle of measuring, as distinguished from counting. 4. A computer that solves problems by setting up equivalent electric circuits and making measurements as the variables are changed in accordance with the corresponding physical phenomena. An analog computer gives approximate solutions, whereas a digital computer gives exact solutions. 5. A nondigital computer that manipulates linear (continuous) data to measure the effect of a change in one variable on all other variables in a particular problem. (Compare: digital computer.) analog computing -Computing system in which continuous signals represent mechanical (or other) parameters. analog data -1. A physical representation of information such that the representation bears an exact relationship to the original information. The electrical signals on a telephone channel are an analog data representation of the original voice. 2. Data represented in a continuous form, as contrasted with digital data represented in a discrete (discontinuous) form. Analog data is usually represented by physical variables, such as voltage, resistance, rotation, etc. analog input module-An UO rack module that converts an analog signal from a user device to a digital signal that may be processed by the processor. analog meter -An indicating instrument that employs a movable coil and pointer arrangement (or equivalent) to display values along a graduated scale. analog multiplexer-1. Circuit used for timesharing of analog-to-digital converters between a number of different analog information channels. Consists of a group of analog switches arranged with inputs connected to the individual analog channels and outputs connected in common. 2. Two or more analog switches with separate inputs and a common output, with each gate separately controllable. Multiplexing is performed by sequentially turning on each switch one at a time, switching each individual input to a common output. 3. A device that selects one of several analog signals according to a digital code. Analog multiplexers (amux) are available in many forms; their chief application is as a front end in data-acquisition systems, enabling a single analog-to-digital converter to monitor more than one information channel. analog network -A circuit or circuits that represent physical variables in such a manner as to permit the expression and solution of mathematical relationships between the variables, or to permit the solution directly by electric or electronic means.

analog output - AN

25

analog output-1. A signal (voltage) whose amplitude is continuously proportionate to the stimulus, the proportionality being limited by the resolution of the device. 2. An output quantity that varies smoothly over a continuous range of values rather than in discrete steps. analog panel meter-See APM. analog recording-A method of recording in which same characteristic of the record current, such as amplitud'e or frequency, is continuously varied in a manner analolgous to the time variations of the original signal. analolg representation -A representation that does not have discrete values, but is continuously variable. analog signal - 1. An electrical signal that varies continuously in both time and amplitude, as obtained from temperature or pressure, or speed transducers. A voltage level that changes in proportion to the change in a physical variable. 2. A signal representing a variable that may be continuously observed and continuously represented. analog s w i t c h -1. A device that either transmits an analog signal without distortion or completely blocks it. 2. An:y solid-state device, with or without a driver, capable of bilaterally switching voltages or current. It has an input terminal, output terminal, and, ideally, no offset voltage, low on resistance, and extreme isolation between the signal being gated and control signals. 3. A means to interconnect two or more circuits whose information is represented in analog form using a network that may or .may not be time divided and may or may not consist of linear elements. analog-to-digital conversion -1. The process of (converting a continuously variable (analog) signal to a (digital signal (binary code) that is a close approximation of the original signal. 2. The process of quantizing a rcontinuous function. analog-to-digital converter-Abbreviated a-d converter, adc, or ADC. 1. A circuit that changes a continuously varying voltage or current (analog) into a digital output. The input may be ac or dc, and the output may be seriai or parallel, binary or decimal. 2. Device that translates analog signals (voltages, pressures, etc.) from sensors in.to numerical digital form (binary, decimal, etc.).

I'N

Analytical Engine-An early form of generalpurpose digital computer invented in 2833 by Charles Babbage. analyzer- 1. An instrument or other device designed to examine the functions of components, circuits, or systems and their relations to each other, as contrasted with an instrument designed to measure some specific parameter of such a system or circuit. 2. Of computers, a routine the purpose of which is to analyze a program written for the same or a different computer. This analysis may consist of summarizing instruction references to storage and tracing sequences of jumps. 3. An instrument that evaluates and/or measures one or more specific parameters (e.g.9 voltage, current, frequency, logic level, bit time, distortion). 4. A test assembly that checks the performance of, or locates trouble in, electronic equipment. Also called test set and tester. anastigmat-A lens system designed so as to be free from the aberration called astigmatism. anchor-An object, such as a metal rod, set into the ground to hold the end of a guy wire. ancillary equipment -Equipment not directly employed in the operation of a system but necessary for logistic support, preparation for flight, or assessment of target damage; e.g., test equipment, vehicle transport. AND circuit-Synonym for AND gate. AND device-A device that has its output in the logic 1 state if and only if all the control signals are in the logic 1 state. Anderson bridge -A bridge normally used for the comparison of self-inductance with capacitance. It is a six-branch network in which an outer loop of four arms is formed by four nonreactive resistors and the unknown inductor. An inner loop of three arms is formed by a capacitor and a fifth resistor in series with each other and in parallel with the arm opposite the unknown inductor. The detector is connected between the junction of the capacitor and the fifth resistor and at that end of the unknown inductor separated from a tePmind of the capacitor by only one resistor. The source is connected to the other end of the unknown inductor and to the junction of the capacitor with two resistors of the outer loop. The balance is independent of frequency.

0

D/A CONVERTER

Anderson bridge.

Analog-to-digital converter.

analog transmission -Transmission of a continuously variable signal as opposed to a discretely variable one. analog value -A continuously variable value, such a s a current or voltage.

AND gate- 1. In an electronic computer. a gate circuit with more than one control (input) terminal. No output signal will be produced unless a pulse is applied to all inputs simultaneously. 2. A binary circuit, with two or more inputs and a single output, in which the output is logic 1 only when all inputs are logic I, and the output is logic 0 if any one of the inputs is logic 0. AND/NOR gate-A single logic element that performs the operation of two AND gates with outputs feeding a NOR gate. No access to the internal logic elements is provided (ie., no connection is available at the outputs of the AND gates).

AND/OR circuit

- angle of incidence

26

L I

I

,

AND GATE (SCHEMATIC)

D*:C

AND GATE (LOGIC DIAGRAM)

AND gate with three inputs.

AND/OR circuit-A gating circuit that produces a prescribed output condition when several possible combinations of input signals are applied. It exhibits the characteristics of the AND gate and the OR gate. android - 1. A mobile mechanism possessing the ability to manipulate objects external to itself under the constant control of its own resident intelligence, operating within guidelines initially established and occasionally updated by a human being, a computer, or some other external intelligence. 2. Automaton of manlike form. a n e c h o i c -Nonreflective, producing no echoes. anechoic chamber-1. A room or chamber specially designed to absorb all sound within, thus preventing sound reflections or reverberation. Such rooms are used for evaluation of microphones and speakers. 2. A room lined with material that traps sound waves so the sound is perfectly absorbed and the room is acoustically dead. Such a chamber is used for testing microphones and speakers. 3. A derived term for a room or enclosure that is designed to be echo free over a specified frequency range. Any sound reflections within this frequency range must be less than 10 percent of the source sound pressure. a n e c h o i c enclosure -A special echo-free enclosure used for testing audio transducers, in which all wall surfaces have been covered with acoustically absorbent materials so that reflections of the sound waves are eliminated. Also known as a dead room or an anechoic room. a n e c h o i c room-A room whose walls have been treated so as to make them absorb a particular kind of radiation almost completely; used for testing components of sound systems, radar systems, etc., in an environment free of reflections. anelectronic-See anelectrotonus. anelectrotonus -The reduced sensitivity produced in a nerve or muscle in the region of contact with the anode when an electric current is passed through it. anemometer -An instrument used for measuring the force or speed of wind. angels -Short-duration radar reflections in the lower atmosphere. Most often caused by birds, insects, organic particles, tropospheric layers, or water vapor. angle- 1. A fundamental mathematical concept formed when two straight lines meet at a point. The lines are the sides of the angle, and the point of intersection

0"

90"

-F

180"

270"

360"

Angle.

is the vertex. 2. A measure of the distance along a wave or part of a cycle, measured in degrees. 3. The distance through which a rotating vector has progressed. angle jamming -An electronic countermeasures technique in which azimuth and elevation information present in the modulation components of the returning echo pulse of a scanning fire-control radar is jammed by transmitting a pulse similar to the radar pulse but with angle information of erroneous phase. angle modulation-Modulation in which the angle of a sine-wave carrier is the characteristic varied from its normal value by modulation. Phase and frequency modulation are particular forms of angle modulation. angle noise-Tracking error introduced into radar by variations in the apparent angle of arrival of the echo from a target due to finite target size. (This effect is caused by variations in the phase front of the radiation from a multiple-point target as the target changes its aspect with respect to the observer.) angle of arrival-Angle made between the line of propagation of a radio wave and the earth's surface at the receiving antenna. angle of azimuth -The angle measured clockwise in a horizontal plane, usually from the north. The north used may be true north, Y-north, or magnetic north. angle of beam-The angle that encloses most of the transmitted energy from a directional-antenna system. angle of convergence -Angle formed by the lines of sight of both eyes when focusing on an object. angle of deflection-The angle formed between the new position of the electron beam in a cathode-ray tube and the normal position before deflection. angle of departure-The angle of the line of propagation of a radio wave with respect to a horizontal plane at the transmitting antenna. angle of divergence-In cathode-ray tubes, a measure of its spread as the electron beam travels from the cathode to the screen. The angle formed by an imaginary center line and the border line of the electron beam. In good tubes, this angle is less than 2". angle of elevation-The angle between the horizontal plane and the line ascending to the object. angle of incidence-The angle between a wave or beam striking a surface and a line perpendicular to that surface.

21

angle of lag -The angular phase difference between one sinusoidal function and a second having the same frequency. Expressed in degrees, the amount the second function must be retarded to coincide with the first.

Angle of lag.

angle! of lead- 1. The time or angle by which one alternating electrical quantity leads another of the same cyclic period. 2. The angle through which the commutator brushes of a generator or motor must be moved from the normal position to prevent sparking.

B A LEADS 8 BY 90"

Angle of lead, 1.

angle sf radiation -The angle between the surface of the earth and the center of the beam of energy radiated upward into the sky from a transmitting antenna. angle of reflection-The angle between a wave or beam reflected from a surface and a line perpendicular to that surface. This angle lies in a common plane with the angle of incidence and is equal to it. angle of refraction-The angle between a wave lor beam as it passes through a medium and a line perpendicular to the surface of that medium. This angle lies in a common plane with the angle of incidence. angle tracking noise-Any deviation of the tracking axis from the center of reflectivity of a target. The resultant of servo noise, receiver noise, angle noise, and amplitude noise. angstrom unit-A unit of measurement of wavellength of light and other radiation. Equal to one ten-thousof a micrometer or one hundred-millionth andth ( of a centimeter cm). The visible spectrum extends from about 4000 to 8000 angstrom units. Blue light has a wavelength in the region of 4700 angstroms; yellow, 5800; and red!, 6500. A measure of wavelength equal to meter, or 0.1 nanometer, the preferred term. a n g u l a r acceleration -The rate at which angular velocity changes with respect to time, generally expressed in radians per second. angular accelerometer-A device capable of measuring the magnitude of, and/or variations in, angular acceleration. a n g u l a r aperture-The largest angular extent of wave surface that an objective can transmit. angular deviation loss-The ratio of the response of a microphone or speaker on its principal axis to the response at a specified angle from the principal axis (expressed in decibels). angular distance -The angle subtended by two bodies at the point of observation. It is equal to the

distance of wavelengths multiplied by 2n radians or by 360". angular frequency-Frequency expressed in radians per second. It is equal to the number of hertz (cycles per second) multiplied by 2n. angular length -Length expressed in radians or equivalent angular measure equal to 2 n radians, or 360", multiplied by the length in wavelengths. angular momentum-The momentum that a body has by virtue of its rotational movement. angular p h a s e difference-Phase difference between two sinusoidal functions expressed as an angle. angular rate -The rate of change of bearing. angular resolution-The ability of a radar to distinguish between two targets solely on the basis of angular separation. angular velocity-The rate at which an angle changes. Expressed in radians per second, the angular velocity of a periodic quantity is the frequency multiplied by 2n. If the periodic quantity results from uniform rotation of a vector, the angular velocity is the number of radians per second passed over by the rotating vector. Generally designated by the Greek letter omega (w). a n h a r m o n i c oscillator- An oscillating system in which the restoi-ing force is a nonlinear function of the displacement from equilibrium. anhysteresis-The process whereby a material is magnetized by applying a unidirectional field upon which is superimposed an alternating field of gradually decreasing amplitude. ANIK-The Canadian domestic satellite system used to transmit the network television feeds of the Canadian Broadcasting Corporation. All ANIK satellites are operated by TeleSat Canada of Ottawa. A N K satellites have both 4-GHz C-band and 12-GHz Ku-band transponders. ANIK means brother in Innit (Eskimo). animation -A moving on-screen representation of the activities taking place in a simulation. anion - 1. A negatively charged ion which, during electrolysis, is attracted toward the anode. A corresponding positive ion is called a cation. 2. A negative ion that moves toward the anode in a discharge tube, electrolytic cell, or similar device. anisotropic- 1. Describing a substance that exhibits different magnetic, electrical, optical, and other physical properties when measured along axes in different directions. 2. A material that has characteristics such as wave propagation constant, magnetic permeability, conductivity, etc., that vary with direction; that is, not isotropic. anisotropic body-A body in which the value of any given property depends on the direction of measurement, as opposed to a body that is isotropic. anisotropic magnet -A magnetic material having a better magnetic characteristic along the preferred axis than along any other. anisotropic material -A material having preferred orientation so that the magnetic characteristics are superior along a particular axis. This may be as a result of rolling, heat treatment in a magnetic field, or, in the case of some of the sintered magnets, the direction of press. anisotropy- Directional dependence of magnetic properties, leading to the existence of easy or preferred directions of magnetization. Anisotropy of a particle may be related to its shape, to its crystalline structure, or to the existence of strains within it. anneal -1. To heat a metal to a predetermined temperature and then let it cool slowly. This process prevents brittleness and often stabilizes electrical characteristics.

annealed laminations

- anodic protection

2. To heat and then gradually cool in order to relieve mechanical stresses. Annealing copper makes it softer and less brittle. annealed laminations -Laminations that have been annealed for transformers or choke coils. annealed wire-Wire that has been softened by heating and gradual cooling to remove mechanical stresses. annotation -An added descriptive comment or explanatory note. annular -Ringed; ring-shaped. annular conductor -A conductor consisting of a number of wires stranded in three reversed concentric layers surrounding a saturated hemp core. The core is usually made wholly or mostly of nonconducting material. This construction has the advantage of lower total ac resistance for a given cross-sectional area of conducting material by eliminating the greater skin effect at the center. annular transistor-A mesa transistor in which the semiconductor regions are arranged in concentric circles about the emitter. annulling network- An arrangement of impedance elements connected in parallel with filters to annul or cancel capacitive or inductive impedance at the extremes of the passband of a filter. annunciation relay- 1. An electromagnetically operated signaling apparatus that indicates whether a current is flowing or has flowed in one or more circuits. 2. A nonautomatic reset device that gives a number of separate visual indications upon the functioning of protective devices, and which may also be arranged to perform a lockout function. annunciator-1. A visual device consisting of a number of pilot lights or drops. Each light or drop indicates the condition that exists or has existed in an associated circuit and is labeled accordingly. 2. A device for sounding an alarm or attracting attention. The indication is usually aural, but occasionally may be visual or both aural and visual. 3. An alarm-monitoring device that consists of a number of visible signals, such as flags or lamps indicating the status of the detectors in an alarm system or systems. Each circuit in the device is usually labeled to identify the location and condition being monitored. In addition to the visible signal, an audible signal is usually associated with the device. When an alarm condition is reported, a signal is indicated -visible, audible, or both. The visible signal is generally maintained until reset either manually or automatically. anode- 1. The positive electrode, such as the plate of a vacuum tube; the element to which the principal stream of electrons flows. 2. In a cathode-ray tube, the electrodes connected to a source of positive potential. These anodes are used to concentrate and accelerate the electron beam for focusing. 3. The less noble and/or higher-potential electrode of an electrolytic cell, at which corrosion occurs. This may be an area on the surface of a metal or alloy, the more active metal in a cell composed of two dissimilar metals, or the positive electrode of an impressed-current system.

+NoDY TRIODE

Anode.

DIODE

28

anode-balancing coil -A set of mutually coupled windings used to maintain approximately equal currents in anodes operating in parallel from the same transformer terminal. anode b r e a k d o w n voltage -The potential required to cause conduction across the main gap of a gas tube when the starter gap is not conducting and all other tube elements are held at cathode potential. a n o d e - b y p a s s capacitor- Also called platebypass capacitor. A capacitor connected between the anode and ground in an electron-tube circuit. Its purpose is to bypass high-frequency currents and keep them out of the load. anode characteristic curve-A graph that shows how the anode current of an electron tube is affected by changes in the anode voltage. anode circuit breaker-A device used in the anode circuits of a power rectifier for the primary purpose of interrupting the rectifier circuit if an arcback should occur. anode current-The electron flow in the element designated as the anode. Usually signifies plate current. anode d a r k space-In a gas tube, a narrow, dark zone next to the surface of the anode. anode dissipation -The power dissipated as heat in the anode of an electron tube because of the bombardment by electrons and ions. anode efficiency-See plate efficiency. anode-load impedance -See plate-load impedance. anode modulation -See plate modulation. anode neutralization -Also called plate neutralization. A method of neutralization in which a portion of the anode-cathode ac voltage is shifted 180" and applied to the grid-cathode circuit through a neutralizing capacitor. anode power input-See plate power input. anode power supply-The means for supplying power to the plate of an electron tube at a more positive voltage than that of the cathode. Also called plate power supply. anode pulse modulation-See plate pulse modulation. anode rays-Positive ions coming from the anode of an electron tube; these ions are generally due to impurities in the metal of the anode. anode saturation-See plate saturation. anode s h e a t h -A layer of electrons surrounding the anode in mercury-pool arc tubes. anode strap -A metallic connector between selected anode segments of a multicavity magnetron, used principally for mode separation. anode supply-Also called plate supply. The dc voltage source used in an electron-tube circuit to place the anode at a high positive potential with respect to the cathode. anode terminal -1. In a diode (semiconductor or tube), that terminal to which a positive dc voltage must be applied to forward-bias the diode. Compare with cathode terminal. 2. In a diode (semiconductor or tube), that terminal at which a negative dc voltage appears when the diode is employed as an ac rectifier (blocking). 3. That terminal which is internally connected to the anodic element of any device. anode voltage -The potential difference existing between the anode and cathode. anode voltage drop (of a glow-discharge, cold c a t h o d e tube) -Difference in potential between cathode and anode during conduction, caused by the electron flow through the tube resistance (ZR drop) anodic protection -Corrosion inhibition based on the electrolytic formation of a protective passive film on

anodic silver

29 metals by applying to them a positive (anodic) potential; e.g., alurninum is anodized (oxidized) by a positive charge in a sulfuric acid solution. anodic silver-A precious metal used in plating; fine silver in different configurations, such as shot, cones, bars, etc., is sacrificed during the silver-plating process. anodization-The formation of an insulating oxide over certain elements, usually metals, by electrolytic action. The most commonly anodized materials are tantalum, aluminum, titanium, and niobium. Anodization is particularly useful where protection of a conductor is required. The base metal can form the conductor and the anodized surface layer can form the insulator. anodke- To deposit a protective coating of oxide on a metal by means of an electrolytic process in which it is used as the anode. anodiizing-An electrochemical oxidation process used to improve the corrosion resistance or to enhance the appearance of a metal surface. Aluminum and magnesium parts are frequently anodized. anomalous displacement current -Also called dielectric absorption. The current in addition to the normal leakage current in a circuit containing a capacitor with an imperfect dielectric after the normal charging or discharging current has become negligibly small. anomalous photoconductivity-A spectral phenomenon in which the degree of the photoresponse of an illumilaated semiconductor is determined by the wavelength colmposition of the incident light. anomalous propagation - 1. Propagation that is Enusual or abnoimal. 2. The conduction of UHF signals through atmospheric ducts or layers in a manner similar to that of a waveguide. These atmospheric ducts carry the signals with less than normal attenuation over distances far beyond the optical path taken by UHF signals. Also 'called sulperrefraction. 3. In sonar, pronounced and rapid variations in the strength of the echo due to large, rapid focal fluctuations in propagation conditions. ~ n o n ~ f FTP ~ o (File ~ s Transfer Protocol) -The .procedure of connecting to a remote computer as an ,anonymous or guest user in order to transfer public files lback to a local computer. See also FTP; protocol. ri3db range-A navigational aid that provides uiisignal zones for aircraft guidance. Deviation from the assigned course is indicated aurally by the Morse code letters A (--) or N (-.). On-course position is jmdicated by an audible merging of the A and N code !si nuous tone. an National Standards Institute. The 1u rganization with responsibility for the development and promulgation of (among others) data

signal --A

- antenna bandwidth

tripped by a unique access code, a short predetermined message is broadcast. answerback unit -An electromechanical device used with a teletypewriter set to transmit a predetermined message of not more than 21 characters in response to a request signal. It can transmit either a five-level 7.42 unit code or an eight-level 11.0 unit code at speeds of up to 100 words per minute. answering cord-The cord nearest the face of a telephone switchboard. It is used for answering subscriber's calls and calls on incoming trunks. answering service- A business that contracts with subscribers to answer incoming telephone calls after a specified delay or when scheduled to do so. It may also provide other services, such as relaying fire or intrusion alarm signals to proper authorities. answer lamp-In a telephone switchboard, a lamp that lights when an answer cord is plugged into a line jack; it extinguishes when the telephone answers and lights when the call is complete. answer tone -Tone signal, with a frequency between 2025 and 2225 Hz and a duration of at least 1.5 s, used by an answering modem to indicate its ready condition to an originating modem. antenna- Also called aerial. 1. That portion, usually wires or rods, of a radio transmitter or receiver station used for radiating waves into or receiving them from space. It changes electrical currents into electrornagnetic radio waves, and vice versa. 2. A section of wire or a metallic device designed to intercept radio waves in the air and convert them to an electrical signal for feeding to a receiver. Under relatively difficult reception conditions, such as created by location, terrain, obstructions, etc., an antenna becomes fairly critical and should be one especially designed for its intended purposes. 3. A device for transmitting and receiving radio waves. Depending on their use and operating frequency, antennas can take the form of a single piece of wire, a dipole, a grid such as a yagi array, a horn, a helix, a sophisticated parabolic-shaped dish, or a phase array of active electronic elements of virtually any flat or convoluted surface. 4. A device that collects and focuses electromagnetic energy, Le., contributes an energy gain. Gain is proportional to surface area for a microwave dish. antenna array- 1. A combination of antennas assembled to obtain a desired pickup or rejection pattern. 2. An arrangement of two or more directional antennas, spaced and connected so that they are in phase and their effects are electrically additive.

radio-range, quadrant-designation ilot whether he or she is on

keyboard -Abbreviation for American National Standards Institute keyboard. A typewriter standard unit that offers a choice of uppercase characters only or uppercase and lowercase combined. series of standards recomANSI s t a n d a r d s - A mended by the American National Standards Institute. a n s w e r b a c k - 1. The response of a terminal to remote-control signals. 2. A signal sent by a data receiver to a data transmitter indicating that it is ready to receive data or is acknowledging the receipt of data. See also handshaking. 3. -A reply message from a terminal, manually or automatically initiated, to verify that the right terminal has been accessed and is in operation. a n s w e r b a c k (W-R-U) s y s t e m -A system capable of being remotely controlled by another station. When

Antenna array.

antenna bandwidth- 1 . The range of frequencies over which the impedance characteristics of the antenna are sufficiently uniform that the quality of the radiated signal is not significantly impaired. 2. The frequency range

antenna beam width - antenna impedance over which a certain antenna characteristic falls within acceptable limits. For instance, an antenna may have a bandwidth of 1 MHz over which the standing-wave ratio is 2 : 1 or less. 3. The frequency range throughout which an antenna will operate at a specified efficiency without the need for alteration or adjustment. antenna beam width-The angle, in degrees, between two opposite half-power points of an antenna beam. antenna coil -In a radio receiver or transmitter, the inductance through which antenna current flows. antenna coincidence-That instance when two rotating, highly directional antennas are pointed toward each other. antenna-conducted interference-Any signal that is generated within a transmitter or receiver and appears as an undesired signal at the antenna terminals of the device, e.g., harmonics of a transmitter signal, or the local-oscillator signal of the receiver. antenna cores-Ferrite cores of various cross sections for use in radio antennas.

POWERED-IRON CORE

WINDING

Antenna core.

antenna coupler -1. A radio-frequency transformer used to connect an antenna to a transmission line or to connect a transmission line to a radio receiver. 2. A radiofrequency transformer, link circuit, or tuned line used to transfer radio-frequency energy from the final plate-tank circuit of a transmitter to the transmission line feeding the antenna. antenna crosstalk-A measure of undesired power transfer through space from one antenna to another. Usually expressed in decibels, the ratio of power received by one antenna to the power transmitted by the other. antenna current -The radio-frequency current that flows in an antenna. antenna detector-A device consisting of an antenna and electronic equipment to warn aircraft crew members of their being observed by radar sets. The device is usually located in the nose or tail of the aircraft and illuminates a light on one or more panels when radar signals are detected. antenna diplexer-A coupling device that permits several transmitters to share one antenna without troublesome interaction. antenna-directivity d i a g r a m -A curve rcprcscnting, in polar or Cartesian coordinates, a quantity proportional to the gain of an antenna in the various directions in a particular plane or cone. antenna disconnect s w i t c h -A safety switch or interlock plug used to remove driving power from the antenna to prevent rotation while work is being performed. antenna duplexer-A circuit or device that permits one antenna to be shared by two transmitters without undesirable interaction. antenna effect -1. Cause of error in a loop antenna due to the capacitance to ground. 2. In a navigational system, any undesirable output signal that results when a directional antenna acts as a nondirectional antenna. 3. The tendency of wires or metallic bodies to act as antennas, i.e., to radiate or pick up radio signals.

30

antenna effective area-In any specified direction, the square of the wavelength multiplied by the power gain (or directional gain) in that direction, and divided by 4n. (When power gain is used, the effective area is that for power reception; when directive gain is used, the effective area is that for directivity.) antenna efficiency-The relative ability of an antenna to convert rf energy from a transmitter into electromagnetic waves. If the gain rating of a directional antenna is 10 dB, for example, it is often assumed that the effective radiated power will be 10 times greater than the rf power fed to it. However, if the antenna efficiency is, say, 50 percent, a loss of 3 dB,the true gain will be only 7 dB (10 - 3 = 7 dB). antenna elevation-The physical height of an antenna above the earth. antenna factor-The value of decibel that must be added to a two-terminal voltmeter reading to obtain the actual induced antenna open-circuit voltage or the electric-field strength. antenna farm-A large plot of ground (5 to 2000 acres) surrounding a radio transmitting or receiving station that provides space and adequate clearance for the installation of several large antennas, such as rhombic antennas. antenna field-1. The region defined by a group of antennas. 2. A group of antennas placed in a geometric configuration that is specific for a particular trajectory measuring system. 3. The effective free-space energy distribution produced by an antenna or group of antennas. antennafier -An integrated low-profile antenna and amplifier for use with compact, portable communications systems. antenna front-to-back ratio-The ratio of field strength in front of a directional antenna (i.e., directly forward in the line of maximum directivity) to the field strength in back of the antenna (i.e,, 180” from the front). Measured at a fixed distance from the radiator. antenna gain- 1. The effectiveness of a directional antenna in a particular direction, compared against a standard (usually an isotropic antenna). The ratio of standard antenna power to the directional antenna power that will produce the same field strength in the desired direction. 2. The increase in signal level at the antenna terminals with reference to the level at the terminals of a half-wave dipole antenna, expressed in decibels. 3. For a given antenna, the ratio of signal strength (received or transmitted) to that obtained with a simple dipole antenna. antenna ground system-That portion of an antenna closely associated with the earth and including an extensive conducting surface, which may be the earth itself. a n t e n n a height -The average height above the terrain from 2 to 10 miles (3.2 to 16 km) from the antenna. In general, the antenna height will be different in each direction from the antenna. The average of these various heights is considered the antenna height above average terrain. antenna height above average terrain-The height of the center of radiation of an antenna above an averaged value of the elevation above sea level for the surrounding terrain. antenna illumination -Describes how a feedhorn “sees” the surface of a dish as well as the surrounding terrain. antenna impedance-The impedance an antenna presents to a transmitter or receiver at the attachment point of the transmission line or feeder. It varies from about 50 to 600 ohms, depending on antenna type and installation.

antenna induced microvolts - anticoincidence circuit

31

antenna induced microvolts-The voltage that exists across the open-circuited antenna terminals, as calculated from a measurement. antenna Iens-An arrangement of metal vanes or dielectric material used to focus a microwave beam in a manner similar to an optical lens. antenna lobe-See lobe. antenna matching -Selection of components to make the impedance of an antenna equal to the characteristic impedance of its transmission line. antennamitter- An integrated low-profile antenna and oscillator for use with compact, portable communications systems. antenna pair-Tko antennas located on a base line of accurately surveyed length. The signals received by these antennas are used to determine quantities related to a target position. antenna pattern -Also called antenna polar diagram. A plot of angle versus free-space field intensity at a fixed distance in the horizontal plane passing through the center of the antenna.

Antenna pattern.

antenna-pattern measuring equipment Devices used to measure the relative field strength or intensity existing at any point or points in the space immediately surrounding an antenna. antenna pedestal -A structure that supports an antenna assembly (motors, gears, synchros, rotating joints, etc.). antenna polar diagram-See antenna pattern. antenna polarization -The position of an antenna, with respect to the surface of the earth, that determines the wave polarization for which the antenna is most efficient. A vertical antenna radiates and receives vertically polarized waves; a horizontal antenna radiates and receives horizontally polarized waves broadside bo itself and vertically polarized waves at high angles off its ends. antenna power-The square of the antenna current of a transmitter, multiplied by the antenna resistance at the point where the current is measured. antenna power gain-The power gain of an antenna in a given direction is four times the ratio of the radiation intensity in that direction to the total power delivered to the antenna. (The term is also applied to receiving antennas.) antenna preamplifier-A low-noise rf amplifier, usually mast-mounted near the terminals of the receiving antennas, used to compensate for transmission-line loss and thereby improve the overall noise figure. antenna reflector-In a directional-antenna array, an element that modifies the field pattern in order to reduce the field intensity behind the array and increase

it in front. In a receiving antenna, the reflector reduces interference from stations behind the antenna. antenna relay-A relay used in radio stations to automatically switch the antenna to the receiver or transmitter and thus protect the receiver circuits from the rf power of the transmitter. antenna resistance-The total resistance of a transmitting antenna system at the operating frequency. The power supplied to the entire antenna circuit, dwided by the square of the effective antenna current referred to the feed point. Antenna resistance is made up of such components as radiation resistance, ground resistance, radio-frequency resistance of conductors in the antenna circuit, and equivalent resistance due to corona, eddy currents, insulator leakage, and dielectric power loss. antenna resonant frequency-The frequency (or frequencies) at which an antenna appears to be a pure resistance. antenna stabilization-A system for holding a radar beam steady despite the roll and pitch of a ship or airplane. antenna structure-A structure that includes the radiating system, its supporting structures, and appurtenances mounted thereon. antenna switch-Switch used for connecting an antenna to or disconnecting it from a circuit. antenna s y s t e m - An assembly consisting of the antenna and the necessary electrical and mechanical devices for insulating, supporting, and/or rotating it. antenna terminals -On an antenna, the points to which the lead-in (transmission line) is attached. antenna tilt error- The angular difference between the antenna tilt angle shown on the mechanical indicator and the electrical center of the radar beam. antennaverter -A receiving antenna and converter combined in a single unit that feeds directly into the receiver IF amplifier. antenna wire-A wire, usually of high tensile strength, such as coppenveld, bronze, etc., with or without insulation, used as an antenna for radio and electronic equipment. antiaircraft missile -A guided missile launched from the surface against an airborne target. anti-aliasing-The smoothing or removal of diagonal lines in digitized images at low resolutions that appear as stair-steps in order to recreate smoother diagonal lines. anti-aliasing filter-A filter (normally low pass) that band-limits the input signal before sampling to less than half the sampling rate to prevent aliasing noise. anticapacitance switch-A switch with widely separated legs, designed to keep capacitance at a minimum in the circuits being switched. anticathode-Also called target. The target of an X-ray tube on which the stream of electrons from the cathode is focused and from which the X-rays are radiated. anticlutter circuit-In a radar receiver, an auxiliary circuit that reduces undesired reflection in order to pennit the detection of targets that otherwise would be obscured by such reflections. anticlutter gain Control -A device that automatically and gradually increases the gain of a radar receiver from low to maximum within a specified period after each transmitter pulse. In this way, short-range echoes producing clutter are amplified less than long-range echoes. anticoincidence-A nonsimultaneous occurrence of two or more events (usually, ionizing events). anticoincidence circuit -1. A counter circuit that produces an output pulse when either of two input circuits receives a pulse, but not when the two inputs receive

anticollision radar

- antistatic sprays

pulses simultaneously. 2. A circuit that provides an output only when all inputs are absent; a NAND circuit. radar system used in an anticollision radar-A aircraft or ship to warn of possible collision. antiferroelectricity-The property of a class of crystals that also undergo phase transitions from a higher to a lower symmetry. They differ from the ferroelectrics in having no electric dipole moment. antiferroelectric materials- Those materials in which spontaneous electric polarization occurs in lines of ions; adjacent lines are polarized in an antiparallel arrangement. antiferromagnetic materials-Those materials in which spontaneous magnetic polarization occurs in equivalent sublattices; the polarization in one sublattice is aligned antiparallel to the other. antiferromagnetic resonance-The absorption of energy from an oscillating electromagnetic field by a system of processing spins located on two sublattices, with the spins on one sublattice going in one direction and the spins on the other sublattice in the opposite direction. antiferromagnetism -A phenomenon of magnetism characterized by the elimination of magnetic moments and decrease in magnetic susceptibility with a decrease in temperature due to the q u a l power of atomic magnets. antihunt-A stabilizing signal or equalizing circuit used in a closed-loop feedback system of a servomechanism to prevent the system from hunting, or oscillating. Special types of antihunt circuits are the anticipator, derivative, velocity feedback, and damper. antihunt circuit- A circuit used to prevent excessive correction in a control system. antihunt device-A device used in positioning systems to prevent hunting, or oscillation, of the load around an ordered position. The device may be mechanical or electrical. It usually involves some from of feedback. antijamming- 1. Minimizing the effect of enemy electronic countermeasures to permit echoes from targets detected by radar to be visible on the indicator. 2. Controls or circuit features incorporated to minimize jamming. antijamming radar data processing -Use of data from one or more radar sources to determine target range in the presence of jamming. antilogarithm-The number from which a given logarithm is derived. For example, the logarithm of 4261 is 3.6295. Therefore the antilogarithm of 3.6295 is 4261. antimagnetic-Made of alloys that will not remain in a magnetized state. antimicrophonic -Specifically designed to prevent microphonics. Possessing the characteristic of not introducing undesirable noise or howling into a system. antimissile missile-A missile that is launched to intercept and destroy another missile in flight. antinode-The point on a transmission line at which the current is maximum and the voltage is minimum. antinodes-Also called loops. The points of maximum displacement in a series of standing waves. Two similar and equal wave trains traveling at the same velocity in opposite directions along a straight line result in alternate antinodes and nodes along the line. Antinodes are separated from their adjacent nodes by half the wavelength of the wave motion. antinoise carrier-operated device -A device commonly used to mute the audio output of a receiver during standby or no-carrier periods. Usually the automatic volume control voltage is used to control a squelch tube which, in turn, controls the bias applied to the first audio tube so that it is permitted to operate only when a

32 carrier is present at the receiver input. Thus, the receiver output is heard when a signal is received, and is muted when no signal is present. antinoise microphone-A microphone that discriminates against acoustic noise. A lip or throat microphone is an example. antiphase-Two identical signals disposed in 180" phase opposition. When superimposed, they tend to cancel each other because their waveform patterns are of equal magnitude but opposite polarity. antiproton-An elementary atomic particle that has the same mass as a proton but is negatively charged. antirad-A material that inhibits damage caused by radiation. antiresonance-A type of resonance in which a system offers maximum impedance at its resonant frequency. a n t i r e s o n a n t circuit -A parallel resonant circuit offering maximum impedance to the series passage of the resonant frequency. antiresonant frequency- 1. The frequency at which the impedance of a system is very high. 2. Of a crystal unit, the frequency for a particular mode of vibration at which, neglecting dissipation, the effective impedance of the crystal unit is infinite. antisidetone- 1. In a telephone circuit, special circuits and equipment that are so arranged that only a negligible amount of the power generated in the transmitter reaches the associated receiver. 2. Pertaining to the reduction or elimination of interference in telephone circuits between the microphone and earphone of the same telephone. antisidetone circuit-A telephone circuit that prevents sound, introduced in the local transmitter, from being reproduced in the local receiver. (Reduces sidetones.) antisidetone induction coil -An induction coil designed for use in an antisidetone telephone set. antisidetone telephone set-A telephone set with an antisidetone circuit. antiskating bias-A bias force applied to a pivoted pickup arm to counteract the inward force (toward the center of the record) resulting from the drag of the stylus in the groove and the offset angle of the head. antiskating device-A mechanism found on modern phonograph pickups that provides a small outward force on a pickup arm. This counteracts the arm's tendency to move toward the turntable center (inward) due to offset geometry, and reduces stylus/gmve friction. antistatic agents -Methods employed to minimize static electricity in plastic materials. Such agents are of two basic types. Metallic devices that come into contact with the plastics and conduct the static to earth give complete neutralization initially, but because it is not modified, the surface of the material can become prone to further static accumulation during subsequent handling. Chemical additives, which are mixed with the compound during processing, give a reasonable degree of protection to the finished products. antistatic cleaner -Substance used on phonograph records that helps to prevent the buildup of a static charge that attracts dust. antistatic coating -1. An electrically conductive layer for carrying off static charges that could accumulate on a surface. 2. A conductive coating applied to a TV or monitor screen (or on a glass panel immediately in front of the screen) that conducts away any static charge and prevents dust from adhering to the surface of the television. antistatic s p r a y s -Chemical agents which, when applied to circuits and plastic surfaces, leave a conductive

antistickoff voltage

33 coating that acts to repel dust and dirt and changes surface characteristics. Good antistatic sprays will leave a resistivity reading of 20 to 100 megohms per square inch (3-15 MsZ/cm2) on plastics and 100 megohms or more per square inch on glass surfaces. See static eliminators. antistickoff voltage-A small voltage, usually applied to the rotor winding of the coarse synchro control transformer in a two-speed system. The antistickoff voltage acts to eliminate the possibility of ambiguous behavior in the system. antitransmit-receive box- A second transmitreceive switch used in a radar antenna system to minimize absorption of the echo signal in the transmitter circuit during the interval between transmitted pulses. antitransmit-receive s w i t c h -Abbreviated atr switch. An automatic device employed in a radar system to prevent received energy from being absorbed in the transmitter. antitiransmit-receive tube -See atr tube. antivoice-operated transmission-A method of radiocommunication in which a voice-activated circuit prevents the operation Of the transmitter during reception of messages on an associated receiver. aperiodic- 1. Having no fixed resonant frequency or repetitive characteristics or no tendency to vibrate. A circuit that will not resonate within its tuning range is often called aperiodic. 2. Not characterized by predictable periods or steps. aperiodic antenfla -An antenna designed to have a constant impedance over a wide frequency range (for example, a terminated rhombic antenna) due to the suppression of reflections within the antenna system. aperiodic damping -Also called overdamping. The condition of a system when the amount of damping is so large that when the system is subjected to a single disturbance, either constant or instantaneous, the system comes to a position of rest without passing through that position. Although an aperiodically damped system is not strictly an oscillating system, it has such properties that it would become an oscillating system if the damping were sufficiently reduced. aperiodic function-A function having no repetitive characteristics and not repeatable within a specified period. apericadic waveform -A nonrepeating, random, one-shot waveform. aperture -1. In a unidirectional antenna, that portion of tlhe plane surface which is perpendicular to the direction of maximum radiation and through which the major part of the radiation passes. 2. In an opaque disc, the hole or window placed on either side of a lens to control the amount of light passing through. 3. Also called aperture time. The amount of certainty about the exact time when the encoder input was at the value represented by a given output code. In general, the aperture is equal to the conversion time: it may be reduced by the use of sample-and-hold circuits. 4. In an electron gun, the open.mg that determines the size of, and has an effect on, the shape of the electron beam. In television optics, it is the effective diameter of the lens that controls the amount of light reaching the photoconductive or photoemitting image pickup tube. 5. An opening that will pass light, electrons, or other forms of radiation. aperture antenna-A type of antenna whose beam width is determined by the dimensions of a horn, lens, or reflector. aperture compensation -Reduction of aperture distortion by boosting the high-frequency response of a f elevision-camera video amplifier.

- apogee

aperture correction-Compensation for the loss in sharpness of detail because of the finite dimensions of a scanning beam in the horizontal dimension. aperture delay time-The time elapsed from the application of the hold (or encode) command until the sampling switch in a sample-and-hold circuit opens fully and the device actually takes the sample. Aperture delay time is a fixed delay time and is normally not an error source since the hold clock edge can be advanced to compensate for it. aperture distortion-In a television signal, the distortion due to the finite dimension of the camera-tube scanning beam. The beam covers several mosaic globules simultaneously, resulting in a loss of picture detail. aperture illumination -The field distribution in amplitude and phase through the aperture. aperture jitter- Also called aperture uncertainty time. 1. In a sample-and-hold circuit, the time variation or uncertainty with which the switch opens, or the time variation in aperture delay. 2. A source of error in a sampling system, which determines the maximum slew rate limitation of the sampled analog input signal for a given system resolution. aperture mask-Also called shadow mask. A thin sheet of perforated material placed directly behind the viewing screen in a three-gun color picture tube to prevent the excitation of any one color phosphor by either of the two electron beams not associated with that color.

APERTURE MASK

R

G

BLUE GUN

Aperture mask.

aperture plate-A femte memory plate containing a large number of uniformly spaced holes arranged in parallel rows and interconnected by plated conductors to provide a magnetic memory plate. aperture time- 1. In a sample-and-hold circuit, the averaging time of a sample-hold during the sample-tohold transition. 2. The time required by a sample-and-hold device to go from the sample mode into the hold mode, once the hold command has been received. The aperture time is generally a few nanoseconds, measured from the 50-percent point of the mode-control transition to the time when the output stops tracking the input. See aperture, 3. aperture-time uncertainty -The possible variation in aperture time from one sample-to-hold transition to the next. APL -Abbreviation for average picture level. The average luminance level of the part of a television Line between blanking pulses. APM -Abbreviation for analog panel meter. A scaleand-pointer meter capable of indicating a continuous, rather than incremental, range of values from zero to the rated full-scale value. apogee-The point in an elliptical satellite orbit that is farthest from the surface of the earth. Geosynchronous satellites that maintain circular orbits around the earth are

A positive (A+ or A plus)

-AQL

first launched into highly elliptical orbits with apogees of 22,237 miles. When the communication satellite reaches the appropriate apogee, a rocket motor is fired to place the satellite into its permanent circular orbit of 22,237 miles. Also see perigee. A positive (A+ or A plus)-1. Positive terminal of a battery or positive polarity of any other sources of voltage. 2. The terminal to which the positive side of the filament-voltage source of a vacuum tube should be connected. A power supply-A power supply used as a source of heating current for the cathode or filament of a vacuum tube. apparatus- 1. Any complex device. 2. Equipment or instruments used for a specific purpose. apparatus wire and cable-Insulated wire and cable used in connecting electrical apparatus to a power source, also including wire and cable used in the apparatus itself. apparent bearing-The direction from which the signal arrives with respect to some reference direction. apparent power-In an ac circuit, the power value obtained by simple multiplication of current by voltage with no consideration of the effect of phase angle. (Compare with true power.) apparent power loss -For voltage-measuring instruments, the product of nominal end-scale voltage and the resulting current. For cwrent-measuring instruments, the product of the nominal end-scale current and the resulting voltage. For other types of instruments (for example, wattmeters), the apparent power loss is expressed for a stated value of current or voltage. Also called volt-ampere loss. apparent source-See effective acoustic center. Applegate diagram -A graphical representation of electron bunching in a velocity-modulated tube, showing their positions along the drift space. This bunching is plotted on the vertical coordinate, against time along the horizontal axis. applet-A small computer program that performs a simple task. AppleTal k- A networking protocol developed by Apple Computer for communication between Apple Computer products and other computers. This protocol is independent of what network it is layered on. Appleton layer-In the ionosphere, a region of highly ionized air capable of reflecting or refracting radio waves back to earth. It is made up of the F1 and Fz layers. apple tube-A color-television picture tube in which the three colors of phosphors are laid in fine vertical strips along the screen. The intensity of the electron beam is modulated as its sweeps over them so that each color is produced with appropriate brightness. appliance-Any electrical equipment used in the home and capable of being operated by a nontechnical person. Included are units that perform some task that could be accomplished by other, more difficult means, but usually not those used for entertainment (radios, TVs, hi-fi sets, etc.). appliance wire and cable-A classification of Underwriters’ Laboratories, Inc., covering insulated wire and cable intended for internal wiring of appliances and equipment. Each construction satisfies the requirements for use in particular applications. application- 1. The use of a computer for a specific purpose, e.g., designing a brochure or writing a letter. 2. System or problem to which a computer is applied. An application may be of the computational type, in which arithmetic computations predominate, or of the data-processing type, in which data-handling operations predominate. See also application program.

34 application factor-A modifier of the failure rate. It is based on deviations from rated operating stress (usually temperature and one electrical parameter). application-oriented language -1. A programming language that is primarily useful in some specialized area. 2. A problem-oriented programming language whose statements resemble or contain the terminology of the computer user. application program -1. A computer program intended to solve a problem or do a job, as distinct from systems programs, which control the operations of the computer system. 2. A computer program that performs a data-processing function rather than a control operation. 3. A program used to perform some logical or computational task that is important to the user rather than some internal computer function. 4. Software designed for a specific purpose, such as accounts payable, inventory, payroll, and word processing. 5. A computer program that accomplishes specific tasks, such as word processing. application s c h e m a t i c diagram -Pictorial representation using symbols and lines to illustrate the interrelation of a number of circuits. application-specific integrated circuit -See ASIC. applicationssoftware- 1. Aprogramthatdepends on the specific end application and is used to do the real work or apparent work that is visible to the user. Generally this is the software that is used for dedicated computer-based systems (systems designed to perform a single or specific set of functions). Typical applications include food and chemical processing, production control, automotive electronics, computer-controlled sewing machines, photographic equipment (both for computercontrolled cameras and for darkroom computerized processing), energy distribution systems, word processing, mailing lists, payrolls, and inventory. 2. Computer programs that perform specific tasks, such as word processing or database management. applicators (applicator electrodes) -1. In dielectric heating, the electrodes between which the dielectric item is placed and the electrostatic field developed. 2. Appropriately shaped conducting surfaces between which an alternating electric field is established for the purpose of producing dielectric heating. 3. In medical electronics, the electrodes applied to a patient undergoing diathermy or ultrasonic therapy. applied voltage -1. The potential between a terminal and a reference point in any circuit or device. 2. The voltage obtained when measuring between two given points in a circuit with voltage applied to the complete circuit. 3. The voltage presented to a circuit point or system input, as opposed to the voltage drop resulting from current through an element that results from the applied voltage. applique circuit-A special circuit provided to modify existing equipment in order to allow for some special usage. approach-control radar- Any radar set or system used in a ground-controlled approach system, e.g., an airport-surveillance radar, precision approach radar, etc. a p p r o a c h path-In radio aircraft navigation, that portion of the flight path in the immediate vicinity of a landing area where such a flight path terminates at the touchdown point. approved circuit-See protected wireline distribution system. APT -Abbreviation for automatically programmed tool. A high-level or simplified programming language. AQL- Abbreviation for acceptable quality level. A statistically defined quality level, in terms of percent defective accepted on an average of 95 percent of the

aquadag layer

35 time. In other words, a sampling plan with 1 percent AQL passes (accepts) lots 1 percent defective 95 percent of the time. aquadag layer -Trademark of Acheson Industries, Inc. A conductive graphite coating on the inner side walls of some cathode-ray tubes. It serves as an electrostatic shield or as a postdeflection and an accelerating anode. Also applied to outer walls and grounded here it serves, with the inner coating, as a capacitor to filter the applied high vol.tage.

Aquadag coating.

arbiter- The section of a multiprocessor network’s operating system that resolves simultaneous systemresource requests. arbitrary function fitter-A circuit having an output voltage or current that is a presettable, adjustable, usually nonlinear function of the input voltage(s) or current@) fed to it. arbitrary waveform generator-See waveform generator. arbor-See mandrel. arc- 1. A luminous discharge of electricity through a gas. Characterized by a change in space potential in the immediate vicinity of the cathode; this change is approximately equal to the ionization potential of the gas. 2. A prolonged electrical discharge, or series of prolonged discharges, between two electrodes. (Both produce a bright-colored flame, as contrasted with a dim coronaglow discharge). 3. To form an arc. 4. The electric current in a flamelike stream of incandescent gas particles. 5. An electric current through air or across the surface of an insulator associated with high voltage; usually occurs when a contact is opened, or when deenergizing an inductive load. arcback-Also called backfue. Failure of the rectifying action in a tube, resulting from the flow of a principal electron stream in the reverse direction due to the formation of a cathode spot on the anode. This action limits the peak inverse voltage that may be applied to a particular rectifier tube. arc converter-A form of oscillator utilizing an electric arc to generate an alternating or pulsating current. arc discharge- 1. A discharge between electrodes in gas or vapor. Characterized by a relatively low voltage drop and a high current density. 2. The sustained, luminous thermionic discharge between anode and cathode in a gas-filled tube. arc-discharge tube -A gas-filled or mercuryvapor tube that utilizes ionic phenomena for switching, voltage regulation, or rectification. arc drop -The voltage drop between the anode and cathode of a gas rectifier tube during conduction. aredrop loss-In a gas tube, the product of the instantaneous values of arc-drop voltage and current averaged over a complete cycle of operation. arc-drop voltage -The voltage drop between the anode and cathode of a gas rectifier tube during conduction.

- arc-through

arc failure -1. A flashover in the air near an insulation surface. 2. An electrical failure in the surface heated by a flashover arc. 3. An electrical failure in the surface damaged by the flashover arc. arc function -An inverse trigonometric function. arc furnace-An electric furnace heated by arcs between two or more electrodes. architecture- 1. Organizational structure of a computing system, mainly referring to the CPU or microprocessor. 2. The manner in which the basic computer functions are organized and partitioned on the silicon chips. 3. The manner in which a system (such as a network or a computer) or program is structured. archival -Pertaining to long-term storage of data. archival backup-Backing up only files that have been changed since the last backup. archive -1. A procedure for transfemng information from an online storage diskette or memory area to an offline storage medium. 2. To copy computer programs and data onto an auxiliary storage medium, such as a disk or tape, for long-term retention. arcing -The production of an arc, e.g., at the brushes of a motor or ai the contact of a switch. arcing contacts-Special contacts on which the arc is drawn after the main contacts of a switch or circuit breaker have opened. arcing time- 1. The interval between the parting, in a switch or circuit breaker, of the arcing contacts and the extension of the arc. 2. The time elapsing, in a fuse, from the severance of the fuse link to the final intemption of the circuit under the specified condition. arc lamp -Source of brilliant artificial light obtained by an electric arc passing between two carbon rods. The arc is struck by bringing the two rods together and then rapidly separating them. As the arc bums, the carbon rods are vaporized away. A mechanism is employed to keep the space between the two rods constant. This type of lamp is used extensively in motion picture projectors and spotlights. The illuminaticm of the arc lamp is derived from the incandescence of the positive electrode and from the heated, luminous, ionized gases or vapor that surround the arc. arc oscillator-A negative-resistanceoscillator comprising a sustained dc arc and a resonant circuit. arcover-The (usually abrupt) creation of an arc between electrodes, contacts, or plates of a capacitor. arcover resistance-The resistance of a material to the effects of a high-voltage, low-current arc (under prescribed conditions) passing across the surface of the material. The resistance is stated as a measure of total elapsed time required to form a conductive path on the surface (material carbonized by the arc). arcover voltage -Under specified conditions, the minimum voltage required to create. an arc between electrodes separated by a gas or liquid insulation. arc percussive welding-A type of welding in which the materials to be welded are separated by a gap, across which an arc is struck the arc melts the sm-aces of the materials, and the materials are simultaneously brought together. See also pulse arc welding. arc resistance-The length of time that a material can resist the formation of a conductive path by an arc adjacent to the surface of the materid. Also called tracking resistance. arc suppressor-A device, or combination of devices, used for arc suppression. See spark suppressor. arc-through-In a gas tube, a loss of control with the result that a principal electron stream flows in the normal direction during what should be a nonconducting period.

area code - armor area code-A three-digit number code identifying one of the geographic areas of the United States, Canada, and Mexico to permit direct distance dialing on the telephone system. The area code precedes the central office code in the complete 10-digit telephone number, and must be used when the called telephone is in a numbering plan area different from that of the calling telephone. The first digit of the area code is never a 1 or 0. See also direct distance dialing. area protection-Protection of the inner space or volume of a secured area by means of a volumetric sensor. area redistribution-A method of measuring the duration of irregularly shaped pulses. A rectangle is drawn having the same peak amplitude and the same area as the original pulse under consideration. Because the same time units are used in measuring the original and the new pulse, the width of the rectangle is considered the duration of the pulse. area s e n s o r - A sensor with a detection zone that approximates an area, such as a wall surface or the exterior of a safe. A register-The accumulator for all arithmetical operations in a computer. Also called A accumulator. argon-An inert gas used in discharge tubes and some electric lamps. It gives off a purple glow when ionized; its symbol is Ar. argon glow lamp-A glow lamp containing argon gas that produces a pale blue violet light. argument-1. A variable upon which the value of a function depends. The arguments of a function are listed in parentheses after the function name. The computations specified by the function definition are made with the variables specified as arguments. 2. The number that a function works on to produce its results. 3. The independent variable of a function. Arguments can be passed as part of a subroutine call where they would be used in that subroutine. arithmetic and logic unit -Computer element that can perform the basic data manipulations in the central processor. Usually it can add, subtract, complement, negate, rotate, AND, and OR. Abbreviated ALU. arithmetic capability-The ability to do addition, subtraction, and in some cases multiplication and division. arithmetic check-A check of a computation making use of the arithmetical properties of the computation. arithmetic element -Synonym for arithmetic unit. arithmetic mean -1. Usually, the same as average. It is obtained by first adding quantities together and then dividing by the number of quantities involved. 2. A figure midway between two extremes and is found by adding the minimum and maximum together and dividing by two. arithmetic operation-1. In an electronic computer, the operations in which numerical quantities form the elements of the calculation, including the fundamental operations of arithmetic (addition, subtraction, multiplication, comparison, and division). 2. Adding, subtracting, incrementing, or decrementing data in registers or memOrY.

arithmetic organ -See arithmetic unit. arithmetic shift-In a digital computer, the multiplication or division of a quantity by a power of the base used in the notation. arithmetic statement - 1. An expression and a variable separated by an equals sign. The expression is evaluated and the resulting value is assigned to the variable. 2. Instruction specifying an arithmetic operation. arithmetic s u m -The sum of two or more quantities regardless of their signs. Compare with algebraic sum. arithmetic s y m m e t r y -Filter response showing mirror-image symmetry about the center frequency when frequency is displayed on an arithmetic scale. Constant

36 envelope delay in bandpass filters usually is accompanied by arithmetic symmetry in the phase and amplitude responses and generally requires a computer design. See also geometric symmetry. arithmetic unit- Also called arithmetic element or arithmetic organ. In an automatic digital computer, that portion in which arithmetical and logical operations are performed on elements of information. armature-The moving element in an electromechanical device, such as the rotating part of a generator or motor, the movable part of a relay, or the spring-mounted, iron portion of a bell or buzzer. armature contacts- 1. Contacts mounted directly on the armature. 2. Sometimes used for movable contacts. armature control of speed-The varying of voltage applied to the armature of a shunt-wound motor to control the motor’s speed over the basic speed range. armature core -An assembly of laminations forming the magnetic circuit of an armature. armature gap-The space between the armature and pole face. armature hesitation-A delay or momentary reversal of the motion of the armature. armature-hesitation contact chatter-Chatter caused by delay or momentary reversal in direction of the armature motion of a relay during either the operate or the release stroke. armature-impact contact chatter-Chatter caused by impact of the armature of a relay on the pole piece in operation, or on the backstop in release. armature overtravel -That portion of the available stroke occurring after the contacts of a relay have touched. armature reaction-In an armature, the reaction of the magnetic field produced by the current on the magnetic lines of force produced by the field coil of an electric motor or generator. armature rebound-Return motion of a relay armature after striking the backstop. armature-rebound contact chatter-Chatter caused by the partial return of the armature of a relay to its operated position as a result of rebound from the backstop in release. armature relay-A relay operated by an electromagnet that, when energized, causes an armature to be attracted to a fixed pole or poles. armature slot-In the core of an armature, a slot or groove into which the coils or windings are placed. armature stud-In a relay, an insulating member that transmits the motion of the armature to an adjacent contact member. armature travel -The distance traveled during operation by a specified point on the armature of a relay. a r m a t u r e voltage control-A means of controlling the speed of a motor by changing the voltage applied to its armature windings. armature wire -Stranded annealed copper wire, straight lay, soft loose white cotton braid. It is used for low-voltage, high-current rotor winding motors and generators. Straight lay permits forming in armature slots, and compressibility. a r m c h a i r copy- Amateur term for clear, static-free signals. armed sweep -See single sweep. arming t h e oscilloscope sweep -Closing a switch that enables the oscilloscope to trigger on the next pulse. armor -A braid or wrapping of metal, usually steel, placed over the insulation of wire or cable to protect it from abrasion or crushing.

armor clamp - artificial intelligence

37

armor clamp-A fitting for gripping the armor of a cable at the point where the armor terminates or where the cable enters a junction box. armored cable-Two or more insulated wires collectively provided with a metallic covering, primarily to protect the insulated wires from damage. Armstrong frequency-modulation s y s t e m -A phase-shift modulation system originally proposed by E. H. Armstrong. Armstrong oscillator- An inductive feedback oscillator that consists of a tuned gate circuit and an untuned tickler coil in the drain circuit. Feedback is controlled by varying the coupling between the tickler and the gate circuit.

TICKLER

5-25V

Amstrong oscillator.

arr-- See automatic repeat request. array- 1. In an antenna, a group of elements arranged to provide the desired directional characteristics. These elements may be antennas, reflectors, directors, etc. 2. A series of items, not necessarily arranged in a meaningful pattern. 3. The group of patterns on a wafer or in the artwork or photomask for semiconductor processing. See random-access memory. a r r a y antenna -An antenna comprising a number of radiating elements, generally similar, arranged and excited to obtain directional effects. a r r a y device -A group of many similar, basic, complex, or integrated devices without separate enclosures. Each has at least one of its electrodes connected to a common conductor, or all are connected in series. array noise -Unwanted disturbance in a memory integrated circuit generated by the normal movement of data within the array. a r r a y processor-1. A computer optimized in architecture and instruction set to handle programs involving computations on large batches of data, such as fast Fourier transforms and large matrix computations. An array processor takes blocks of data and instructions from a host mini or large computer and performs the computations at speeds many times as high as those that are possible through the host computer alone. The host may be considered the data-organizing front end; the array processor is the processing unit. 2. A computer dedicated by its design to performing repetitive arithmetical calculations on large arrays of data with high precision, wide dynamic range, and high throughput. Usually most input/output operations and file management chores are left to the host computer in order to free the peripheral array processor to concentrate on its calculations. 3. A single computer that operates on one piece of data at a time. 4. A processor in a computer that performs matrix arithmetic much faster than is clone in a standard computer. Capable of performing operations on ail the elements in large matrices at one time. Also called a vector processor.

arrester-Also called a lightning arrester. I. A protective device used to provide a bypass path directly to ground for lightning discharges that strike an antenna or other conductor. 2. A power-line device capable of reducing the voltage of a surge applied to its termnals, interrupting current, if present, and restoring itself to original operating conditions. 3. Device that diverts high voltages to ground and away from the equipment it protects. ARRL -Abbreviation for American Radio Relay League. a r r o w h e a d -A linearly polarized, frequency-independent, log-periodic antenna. ARSR -Abbreviation for air route surveillance radar. ARTCC -Abbreviation for air route traffic control center. A complex data-handling facility designed by Burroughs, IBM, and Raytheon to computerize as much in-route air traffic control as possible. articulation-Sometimes called intelligibility. 1. In a communications system, the percentage of speech units understood by a listener. The word articulation is customarily used when the contextual relationships among the units of speech material are thought to play an unimportant role; the word intelligibility is used when the context is thought to play an important role in determining the listener’s perception. 2. A quantitative measurement of the intelligibility of human speech. where 100 percent is completely understandable. For the typical sound reinforcement or other communications system, no more than a 15-percent articulation loss is acceptable. 3. The ability of a mechanism to pivot, grasp, or extend. articulation equivalent-The articulation of speech reproduced over a complete telephone connection, expressed numerically in terms of the trunk loss of a working reference system that is adjusted to give equal articulation. artificial antenna-Also called dummy antenna. A device that simulates a real antenna in its essential stics and has the necessary power, but which does not radiate or receive radio waves. Used mainly for testing and adjusting transmitters. artificial ear -A microphone-equipped device for measuring the sound pressures developed by an earphone. To the earphone it presents an acoustic impedance equivalent to the impedance presented by the human ear. artificial echo- 1. Received reflections of a transmitted pulse from an artificial target, such as an echo box, comer reflector, or other metallic reflecting surface. 2. A delayed signal from a pulsed radio-frequency signal generator. artificial horizon - A gyroscopically operated instrument that shows, within limited degrees, the pitching and banking of an aircraft with respect to the horizon. Lines or marks on the face of the instrument represent the aircraft and the horizon. The relative positions of the two are then easily discernible. artificial intelligence- Abbreviated AI 1. The design of computer and other data-processing machinery to perform increasingly higher-level cybernetic functions. 2. The capability of a device to perform functions that are normally associated with human intelligence, such as reasoning, learning, and self-improvement. Related to machine learning. 3. The imitation by artificial systems of characteristics described as intelligent when observed in humans. Artificial intelligence embraces concepts and theories from many different disciplines, including mathematics, cybernetics, computer science, psychology, biology, and others. 4. Overlapping subsets called expert systems, knowledge representations, inference schemes, program synthesis, scene analysis, and robotics. 5. The ability of a machine to perform certain complex functions

artificial ionization

- aspect ratio

normally associated with human intelligence, such as judgment, pattern recognition, understanding, learning, planning, and problem solving. 6. Computer programs developed to mimic human intelligence, such as reasoning, learning, problem solving, and making decisions. Artificial intelligence programs enable computers to perform tasks such as playing chess, proving mathematical theorems, etc. 7. An area of computer science dedicated to the development of machines that can learn, understand, interpret, and arrive at conclusions in a manner that would be considered intelligent if a person were doing it. artificial ionization -Introduction of an artificial reflecting or scattering layer into the atmosphere to permit beyond-the-horizon communications. artificial language-In computer terminology, a language designed for ease of communication in a particular area of activity, but one that is not yet natural to that area (as contrasted with a natural language evolved through long usage). artificial line-A lumped-constant network designed to simulate some or all the characteristics of a transmission line over a desired frequency range. artificial line duct- A balancing network simulating the impedance of the real line and distant terminal apparatus. It is employed in a duplex circuit to make the receiving device unresponsive to outgoing signal currents. artificial load-Also called dummy load. A dissipative but essentially nonradiating device having the impedance characteristics of an antenna, transmission line, or other practical utilization circuit. Energy is dissipated in the form of heat. Used to test radio transmitters, engine generators, etc. Permits testing under load conditions without the creation of any standing waves or radiating a signal. artificial radioactivity-Radioactivity induced in stable elements under controlled conditions by bombarding them with neutrons or high-energy, charged particles. Artificially radioactive elements emit beta and/or gamma rays. artificial voice-A small speaker mounted in a specially shaped baffle that is proportioned to simulate the acoustical constants of the human head. It is used for calibrating and testing close-talking microphones. Artos stripper-A machine that, when properly adjusted, will automatically measure to a predetermined length, cut, strip, count, and tie wire in bundles. ARTS -Abbreviation for Automated Radar Terminal System. A multiprocessor computing system used at terminal radar approach controls (tracons) and airport towers, based on Speny Univac 1140 computers. Various configurations, differing in size of memory and number of processors, exist at different facilities; the largest, ARTS IIIE, is installed at the New York tracon. artwork- 1. A topological pattern of an integrated circuit, made with accurate dimensions so that it can be used in mask making. Generally, it is a large multiple of the final mask size, and final reduction is accomplished through the use of a step-and-repeat camera. 2. Detailed, original drawing (often developed with the aid of a computer) showing layout of an integrated circuit. 3. The images formed by drawing, scribing, or by cutting and stripping on a film or glass support, which are reduced, contact-printed, or stepped and repeated to make a photomask or intermediate. 4. Layouts and photographic films created to produce thick-film screens and thin-film masks. ASA- Abbreviation for American Standards Association. See American National Standards Institute. ASA code-A code that was recommended by the American Standards Association for industry-wide use in the transmission of information. Now ANSI code.

38

asbestos -A nonflammable material generally used for heat insulation, such as in a line-cord resistor. No longer used on new equipment. A-scan -Also called A-display. On a cathode-ray indicator, a presentation in which time (range or distance) is one coordinate (horizontal) and signals appear as perpendicular deflections to the time scale (vertical).

PULSE Y

a P

-

RECEIVER NOISE (GRASS)

RANGE

A-scan on a CRT.

ASCII-Acronym for American Standard Code for Information Interchange (pronounced “ask-ee”). 1. A standard code used extensively in data transmission, in which 128 numerals, letters, symbols, and special control codes are each represented by a seven-bit binary number 0000000 through 1111111. For example, numeral 5 is represented by 011 0101, letter K by 100 1011, percent symbol (%)by 010 0101, and start of text (STX) control code by 000 0010.2. A standard code used by many computers, video-display terminals, teleprinters, and computer peripherals. A full eight-bit ASCII word may be transmitted in parallel or serial form, with the eighth bit often providing parity information. Keyboard encoders convert a single switch closure into an ASCII data word; character generators convert stored ASCII data words (and some timing commands) into groups of dots suitable for raster-scan display. A-scope-An oscilloscope that uses an A-scan to present the range of a target as the distance along a horizontal line from the transmitted pulse pip to the target, or echo pip. Signals appear as vertical excursions of the horizontal line, or trace. ASDE-See airport surface detection equipment. as-fired -Values of thick-film resistors or smoothness of ceramic substrates as they come out of the firing furnace prior to trimming and polishing, respectively (if required). AS1 -An abbreviation for standards published by the American Standards Institute. Now American National Standards Institute. ASIC -Abbreviation for application-specific integrated circuit. l. Semiconductor circuits specifically designed to suit a customer’s particular requirement, as opposed to general-purpose parts that can be used in many different systems or applications. 2. An integrated circuit designed to fill the specific requirement of a unique application. ask-See amplitude-shift keying. aspect ratio -1. Ratio of frame width to frame height. 2. The ratio of an object’s height to its width. In graphics this ratio usually pertains to the face of a rectangular CRT or to the characters or symbols drawn by the character generator. 3. The ratio between the length of a film resistor and its width: equal to the number of squares of the resistor. 4. The ratio of the width of a

39 television picture tube to its height. In the United States, the television standard is 4 :3. asplerities-Local microscopic points on an electrode surface at which there is considerable field enhancement. They lead to a dependence of electric strength on electrode area (area effect). aspheric- 1. Not spherical; an optical element having onle or more surfaces that are not spherical. 2. A mirror or lens surface that varies slightly from a true spherical surface. This is done to reduce lens aberrations. ASFl -Abbreviation for automatic send and receive and airport surveillance radar. 1. A terminal equipped with recording devices, usually a paper-tape reader and punch, which is capable of answering a call, recording a message, or sending data loaded in its tape reader without the need for an operator in attendance at the time of the call. Also used to specify terminals that have paper-type equipment used by the operator. 2. A teletypewriter that contains a keyboard, page printer. paper-tape transmitter, and paper-tape punch. Paper tape can be prepared offline, which can take place while hard copy is being received from the line or while other paper tape is being transmitted. -Abbreviation for automatic stereophonic recordiing amplifier. An instrument developed by Columbia Broadcasting System for stereo recording. Compression of the vertical component of the stereo recording signal is automatically decreased or increased as required by the recording conditions. assemble -1. To collect, interpret, and coordinate the data required for a computer program, translate the data into computer language, and project it into the master routine for the computer to follow. 2. To translate from a symbolic program to a binary program by substituting bmary. loperation codes for symbolic operation codes and replacing symbolic addresses with absolute or relocatable addresses. assembler- 1. A program that prepares a program in machine language from a program in symbolic language by substituting absolute operation codes for symbolic operation codes and absolute or relocatable addresses for symbolic addresses. 2. A unit that converts the assembly language of a computer program into the machin(:: language of the computer, accepting mnemonics and symbolic addresses instead of actual binary values for addresses, instructions, and data. 3. A program that accepts instructions, addresses, and data in symbolic form (character stsings that represent machine instructions, addresses, data, among others). Then it automatically translates symbols into their corresponding numerical values. It permits symbolic addressing by assigning values to labels used to indicate program-jump locations. 4. A simple programming language that allows the programmer to define labels and fixed values and to then use these labels with a mnemonic instruction set to produce a machine code program. 5. Program that converts sourcecode (mnemonic) input into op-code (binary) machine language instructions. If such a program were not available, the programmer would have to enter all instructions in ones and zeros, a much more tedious and error-prone procedure. 6. A computer program that converts a higherlevel (Englishlike) programming language into machinereadable instructions. assembler program -Software, usually supplied by the computer manufacturer, to convert an assembly language application program into machine language. assembly- 1. A complete operating unit, such as a radio receiver, made up of subassemblies, such as an amplifier and various components. 2. Process in which instruchons written in symbolic form by the programmer are changed to machine language by (he computer.

assembly language- 1. A computer language that has one-to-one correspondence with an assembly program. The assembly program directs a computer to operate on a program in symbolic language to produce a program in machine language. See also high-order language; machine language, 3; and source language. 2. Grouped alphabet characters, called mnemonics, that replace the numeric instructions of machine language. These mnemonics are easier to remember than machine instructions and hence easier to develop into a working program. 3. A machine-oriented language based primarily on a one-to-one relationship between machine instructions and user-supplied source code. 4. Microprocessor commands written in mnemonic form. Typically, threeletter abbreviations, called mnemonics, are used to represent each instruction, and each mnemonic can usually be equated to one machine-code instruction. 5 . A humanoriented symbolic-mnemonic source language that is used by the programmer to encode programs and associated databases. Assembly language programs are read by the assembler and converted to executable machine language programs during the assembly process. Assembly language is easier to remember and manipulate than machine language. 6. Human-oriented varieties of machine languages. Precisely the same final program code can be produced from an assembler as by hand-coding machine language. However, assembly languages prove more convenient for people than the numeric-only machine languages. assembly-language p r o ~ r a ~ m ~ n bolic-language programming. assembly-output language-An optionai symbolic assembly language listing of the object-code output from a high-level language compiler. Can be quite helpful as a debugging tool because it shows exact machine code in a readable format. assembly program-A program that enables a computer to assemble mnemonic language into machine language; for example, a FORTRAN assembly program. Also called assembly routine. a s s e m b l y robot -A computerized robot, probably a sensory model, designed specifically for assemblyline jobs. For light, batch-manufacturing applications, the arm’s design may be fairly anthropomorphic. assembly routine -See assembly program. assertion checking -Evaluating a program by embedding statements that should always hold true. assignable cause -A definitely identified factor contributing to a quality variation. assigned frequency-The center of the frequency band assigned to a station. assigned f r e q u e n c y band -The frequency band, the center of which coincides with the frequency assigned to the station, and the width of which equals the necessary bandwidth plus twice the absolute value of the frequency tolerance. associative memory-A computer memory in which the data are stored and indexed by content, as in a dictionary, in contrast with the storage of a random-access memory. 2. A memory in which the storage locations are identified by their contents rather than by their addresses. Enables faster interrogation to retrieve a particular data element. associative storage -Computer storage in which locations may be identified by specification of part or all of their contents. Also called parallel-search storage or content-addressed storage. astable- 1. Pertaining to a device that has two temporary states: the device alternates between these states with a period and duty cycle determined by circuit time constants. See also bistable. 2. Refers to a device that

astable circuit

- a s y n c h r o n o u s communication

has two temporary states. The device oscillates between the two states with a period and duty cycle predetermined by time constants. astable circuit -A circuit that continuously alternates between its two unstable states at a frequency determined by the circuit constants. It can be readily synchronized by applying a repetitive input signal of slightly higher frequency. A blocking oscillator is an example of an astable circuit. astable multivibrator (free-running) -A circuit having two momentarily stable states, between which it continuously alternates, remaining in each for a period controlled by the circuit parameters and switching rapidly from one to the other.

A I IN SECONOS.A

IN OHMS c IN FARADS&

Circuit

output.

Astable multivibrator.

astatic- 1. Having no particular orientation or directional characteristics; such as a vertical antenna. 2. Being in neutral equilibrium; having no tendency toward any change of position. astatic galvanometer -A sensitive galvanometer used for detecting small currents. Consists of two small magnetized needles of equal size and strength arranged in parallel and with their north and south poles adjacent, suspended inside the galvanometer coil. Since the resultant magnetic moment is zero, the earth’s magnetic field does not affect the system. A station-One of a pair of transmitting stations in a loran system. The A-station signal always occurs less than half a repetition period after the immediately preceding signal of the other station of the pair and more than half a repetition period before the next succeeding signal of the other station. astigmatism-A type of spherical aberration in which the rays from a single point of an object do not converge on the image, thereby causing a blurred image. Astigmatism in an electron-beam tube is a focus defect in which electrons in different axial planes come to focus at different points. astrionics -Electronics as involved with astronautics.

40

astrocompass -An instrument for determining direction relative to the stars. It is unaffected by the errors to which magnetic or gyrocompasses are subject. astrodome -A rigid hemispherical structure used to cover large tracking instruments to protect them from the elements. It is usually constructed so that the dome rotates with the instrument. astronautics-The science and art of operating space vehicles. astrotracker-A device for tracking stars. A-supply -The A battery, transformer filament winding, or other voltage source that supplies power for heating the filaments of vacuum tubes. a s y c h r o n o u s motor- An ac motor whose speed is not proportional to the frequency of the supply voltage. asymmetrical cell-A cell, such as a photoelectric cell, in which the impedance to the flow of current is greater in one direction than in the other direction. asymmetrical distortion -Distortion affecting a two-condition or binary modulation or restitution, in which all the significant intervals corresponding to one of the two significant conditions have longer or shorter durations than the corresponding theoretical dnrations of the excitation. If this particular requirement is not met, distortion is present. asymmetrical SCR -A fast silicon-controlled rectifier (SCR) with low reverse blocking, which is voltage that causes conduction without an input trigger at the gate input of the SCR. a s y m m e t r i c sideband transmission -See vestigial sideband transmission. a s y m m e t r y control -In pH meters, an adjustment sometimes provided to compensate for differences in the electrodes. asymptote -A line that comes nearer and nearer to a given curve but never touches it. asymptotic breakdown voltage-A voltage that will break down insulation if applied over a long period. a s y n c h r o n o u s - 1. A communication method in which data is sent when it is ready without being referenced to a timing clock, rather than waiting until the receiver signals that it is ready to receive. 2. Transmission in which each data byte is preceded by a start bit and followed by one or more stop bits. Data transmission is intermittent, with an irregular time interval between data bytes. 3. Lacking a regular time relationship; not related through repeating time patterns. Hence, as applied to computer program execution, unexpected or unpredictable with respect to the instruction sequence. 4. Modems, terminals, and transmissions in which each character of information is individually framed (synchronized), usually by start and stop elements. The interval between characters is not fixed. 5. An external interface that can be started and stopped by a microprocessor or other equipment. The opposite is synchronous, which means that the data is randomly available. 6. Having no set pattern, cycle, or speed of transmission. 7. Not synchronized by a clocking signal; in code sets, character codes containing start and stop bits. 8. A mode of data transmission in which time intervals between transmitted characters may be of unequal length. Transmission is independently controlled by start and stop elements at the beginning and end of each character. 9. Pertaining to a mode of data communications that provides a variable time interval between characters during transmission. a s y n c h r o n o u s communication -1. A method of transferring data in which the timing of character placement on connecting communication lines is not critical. Each transferred character is preceded by a start bit and followed by a stop bit, permitting the interval between characters to vary. 2. A relatively simple and

41 cheap system for moving data between machines at speeds up to 1200 or 2400 baud. 3. Data communication of the s t d s t o p type. Each character is sent individually without regular or predictable time relationships with other characters. 4. Method of communications in which data is sent as soon as it is ready. asynchronous computer - 1. An automatic digital computer in which an operation is started by a signal denoting that the previous operation has been completed. 2. A computer in which each operation starts as a result of a signal generated by the completion of the previous operation or by the availability of the equipment required for the next operation. asynchronous device-A device in which the speed of operation is not related to any frequency in the system to which it is connected. asynchronous input/output -The ability to accept input data while simultaneously delivering output data. asynchronous inputs-The terminals that affect the output state of a flip-flop independently of the clock terminads. Called set, preset, reset, or clear; sometimes referred to as dc inputs. asynchronous logic-Logic networks whose operational speed depends only on the signal propagation through the network, rather than on clock pulses as in synchronous logic. asyiichronousmachine- 1. Any machineinwhich its speed of operation is not proportionate to the frequency of the system to which the machine is connected. 2. A multiprocessor system whose processes occur as needed by, and whose operations follow, input data instead of an autonomous clock. asynchronous operation-1. Generally, an operation that is started by a signal at the completion of a previous operation. It proceeds at the maximum speed of the (circuits until it is finished and then generates its own completion signal. 2. A mode in which entry of data into a flip-flop does not require a gating or clock pulse. 3. Operation of a switching network by a free-running signal that triggers successive instructions. The completion of one instruction triggers the next. 4. A computer operation that does not proceed in step with some external timing. ~ s y r ~ ~ h r o n shift o u s register-A shift register that does not require a clock. Register segments are loaded and shifted only at data entry. asyrichronous transmission -Transmission in which each character of the information is synchronized individually (usually by the use of start and stop elements). ATARS -Acronym for Automated Traffic Advisory and Resolution Service. A ground-based automatic collision-avoidance system being developed for use at air terminals. TC - I. Abbreviation for automatic temperature control (General Motors). A means of automatically maintaining desired passenger compartment temperature in a vehicle. Temperature is sensed by a thermistor. Control valves are actuated by a vacuum motor to adjust the proportion of heated or cooled air. 2. Also abbreviation for automated technical control. A computer system used to n control of a data-communication network. - and currents. 3. Wire used to make the internal comniections between the various electrical parts of electronic assemblies. h o p -An excursion of a radio wave from the earth to the ionosphere and back. It is usually expressed as single-, double-, and multihop. The number of hops is called the order of reflection. hopoff-In a potentiometer, the sudden jump in resistance as the contact is rotated over the junction of two resistance slopes. The magnitude of the hopoff is dependeint on the ratio of the slopes and on the junction blending characteristic. h o p p e r -An area in a temporary memory unit, such as a call store, used to record a list of items for subsequent communications with processing programs or input-output programs sent to central control. horizon -An apparent or visible junction of earth and sky as seen on or above the earth. It bounds the part of the earth’s surface that can be reached by the direct wave

FRONT PORCH

HORlZ

TC

9 CYCLES BURST

FREQ BACK PORCH

JLE!;-~ Horizontal blanking puke.

horizontal centering control --In a television receiver or cathode-ray oscilloscope, the adjustment for moving the entire display back and forth. horizontal-convergence control --In a color television receiver, the control that adjusts the amplitude of the horizontal dynamic convergence voltage. horizontal definition -See horizontal resolution. horizontal-deflecting electrodes-A pair of electrodes that move the electron beam from side to side on the screen of a cathode-ray tube employing electrostatic deflection. horizontal-discharge t u b e -A vacuum tube used in the horizontal-deflection circuit to discharge a capacitor and thereby form the sawtooth scanning wave. See also discharge tube. horizontal-drive control -In an electromagnetically deflected television receiver, the control that adjusts the ratio of the pulse amplitude to the linear portion of the scanning-current wave. horizontal dynamic c o n v e r g e n c e -Convergence of the three electron beams in a color picture tube at the aperture mask during scanning of a horizontal line. horizontal field-strength diagram -A representation of the field strength in a horizontal plane and at

horizontal frequency

- horn throat

352

a constant distance from an antenna. Unless otherwise specified, the plane passes through the antenna. horizontal frequency-See line frequency, 1. horizontal hold control-A synchronization control that varies the free-running frequency of the horizontal deflection oscillator so it will be in step with the scanning frequency at the transmitter. horizontal hum bars -Broad, horizontal, moving or stationary bars, alternately dark and light, that extend over an entire television picture. They are caused by interference at approximately 60 Hz or a harmonic of 60 Hz. horizontal-linearity control-In a television receiver, the control for adjusting the width at the left side of the screen. horizontal line frequency-See line frequency, 1. horizontal lock-The circuit that maintains horizontal synchronization in a television receiver. horizontally polarized wave-A linearly polarized wave with a horizontal electric-field vector.

..

I

I

Horizontally polarized wave.

horizontal-output transformer-See flyback transformer. horizontal parabola control-See phase control, 1. horizontalpolarization-1. Transmission in which the electrostatic field leaves the antenna in a horizontal plane. Elements of the transmitting and receiving antennas likewise are horizontal. Horizontal polarization is standard for television in the United States. 2. Transmission of radio waves whose undulations vary horizontally with respect to the earth. (Horizontally polarized antennas are used mainly for base-to-base transmission.) horizontal redundancy checking-See HRC. horizontal repetition rate- Also called horizontal scanning frequency. The number of horizontal lines per second (15,750 hertz in the United States). horizontal resolution-Also called horizontal definition. 1. The number of individual picture elements that can be distinguished in a horizontal scanning line. 2. The capability of a TV system to resolve detail in a horizontal direction across the screen. The higher the resolution number, the sharper the picture will be. 3. The number of vertical lines that can be displayed in a picture width equal to the picture height. This measurement is usually done via direct (RGB or Y/C) input in order to bypass limiting factors such as transmission standards (bandwidth, color carrier, etc.). For standard NTSC (60 Hz, 525 lines, 4 :3 aspect ratio) and PAL (50 Hz, 625 lines, 4 : 3 aspect ratio), the picture is in practice the same: 80 lines per MHz bandwidth. horizontal retrace--. The return of the electron beam from the right to the left side of a CRT raster after the scanning of one line. 2. The line that would be seen on a CRT screen while the spot is returning from right to left, if retrace blanking were not used. horizontal ring-induction furnace -A furnace for melting metal. It comprises an open trough or melting

channel, a primary inductor winding, and a magnetic core that links the melting channel to the primary winding. horizontal-scanningfrequency -See horizontal repetition rate. horizontalsweep -Movement of the electron beam from left to right across the screen or the scene being televised. horizontal-sync discriminator -A circuit employed in the flywheel method of synchronization to compare the phase of the horizontal-sync pulses with that of the horizohtal-scanning oscillator. horizontal-syncpulse -The rectangular pulse that occurs above the pedestal level between each active horizontal line. The pulses keep the horizontal scanning at the receiver in step with that at the transmitter. horn-Also called an acoustic horn. 1. A tubular or rectangular enclosure for radiating or receiving acoustic waves. 2. A primary element consisting of a section of metal waveguide in which one or both of the cross-sectional dimensions increase toward the open end. 3. Any flared or funnel-shaped passage used to couple a speaker efficiently to the air in the environment. It also provides control over sound dispersion pattern over a specified frequency range. The driver is connected to the throat of the horn, and the sound emerges from its mouth. See also horn antenna. horn antenna-Also called a horn. 1. A tubular or rectangular microwave antenna that is wider at the open end and through which radio waves are radiated into space. 2. A microwave antenna formed by flaring the end of a waveguide into the shape of a horn.

REFLECTOR ,TAPERED HORN

Horn antenna.

horn arrester-A lightning arrester that has a spark gap with upward-projecting diversion horns of thick wire. When the arc is formed, it travels up the gap and is extinguished upon reaching the widest part of the gap. horn cutoff frequency-A frequency below which an exponential horn will not function correctly because it fails to provide for proper expansion of the sound waves. horn gap-A type of spark gap with divergent electrodes. horn-gap switch -A form of air switch with arcing horns. horn loading-A method of coupling a speaker diaphragm to the listening space by an expanding air column having a small throat and large mouth. horn loudspeaker-A very directional speaker in which the driver is fed into a metal horn, whose flare is usually an exponential curve. horn mouth-An open-ended metallic device for concentrating energy from a waveguide and directing this energy into space. horn speaker-A speaker in which a horn couples the radiating element to the medium. horn throat-The narrow end of a horn.

353

horsepower

horsepower- Abbreviated hp. A unit of power, or the capacity of a mechanism to do work. It is the equivalent of raising 33,000 pounds 1 foot in 1 minute, (or550 pounds 1 foot in I second. One horsepower equals 146 watts. horseshoe magnet -A permanent magnet or electromagnet shaped like a horseshoe or U to bring the two poles close together.

Horseshoe magnet.

host-- 1. A node computer on a network. The etymology of the term host may be from the days when a computer on a network hosted multiple users and services. 2. Any computer on a network that is a repository for services available to other computers on the network. It is quite cornmon to have one host machine provide several services, such as WWW and Usenet. 3. The primary or controlling computer in a multiple-part system. host computer-1. In the context of networks, a computer that directly provides service to a user. In contrast to a network server, which provides services to a user through an intermediary host computer. 2. The master or controlling computer in a multicomputer network. 3. A computer that prepares programs to be run on another computer system. 4. A computer that monitors and controls other computers and programmable controllers. 5. The central computer (or one of a collection of computers) that provides functions such as computation, database access, or special programs or programming languages; often shortened to host. 6. The central computer (or one of a collection of computers) in a data-communications system, which provides the primary data-processing functions such as computation, database access, or special programs or programming languages. host system-The computer system in which an emulation program or accessory card is used to imitate another system. hot -- 1. Connected, alive, energized; pertains to a terminal or any ungrounded conductor. 2. Not grounded. 3. Strongly radioactive. 4. Excited to a relatively high energy level. 5. Idiomatic term generally used to describe conductcrs carrying an electrical charge. hot-carrier diode -Abbreviated HCD. A diode in which a closely controlled metal-semiconductor junction provides virtual elimination of charge storage. The device has extremely fast turn-on and turn-off times, excellent diode forward and reverse characteristics, lower noise Characteristics, and wider dynamic range. See Schottky barrier diode. hot carriers-In barrier diodes, carriers that have energies greater than those that are in terminal equilibrium with the metal. Thus, electrons that cross the junction from semiconductor to metal must be energetic enough to surmount the barrier. Therefore, electrons that are energetic enough to cross the junction are called hot electrons.

- hot-wire microphone

hot cathode-Also called thermionic cathode. 1. A cathode that supplies electrons by thennionic emission. (As opposed to a cold cathode, which has no heater.) 2. An electron-tube cathode in which electron emission is produced by heat. hot-cathode tube -Also called thermionic tube. Any electron tube containing a hot cathode. hot-cathode X-ray tube- A high-vacuum X-ray tube in which a hot rather than cold cathode is used. hot electrons-See hot carriers. hot-electron triode -A solid-state, evaporatedthin-film structure that is directly equivalent to a triode vacuum tube. hotkey-A single key or a simple key combination that can be used to activate a computer program, or a function in a program. hot line --Communications channel between two points available for immediate use without patching or switching. hot plate-Electrically heated flat surface, sometimes combined with auxiliary equipment such as a magnetic stirrer. hot spot -The point of maximum temperature on the outside of a device or component. hot-spot temperature-The maximum temperature measured on a resistor due to both internal heating and the ambient operating temperature. Maximum hotspot temperature is predicted on thermal limits of the materials and the design. The hot-spot temperature is also usually established as the top temperature on the derating curve at which the resistor is derated to zero power. hot stamping --Method of imprinting letters, numbers, and symbols with a heated die. hot tin dip -A process of passing a bare wire though a bath of molten tin to provide a coating. hot-wire ammeter-Also called thermal ammeter. An ammeter in which the expansion of a wire moves a pointer to indicate the amount of current being measured. The current flows through the wire and changes its length in proportion to 1’. Instability because of wire stretching, and the lack of ambient temperature compensation, make the hot-wire ammeter commercially unsatisfactory.

BINDING

SCALE

POINTER

PO

BINDING ST

/

ADJUSTMENT SCREW

C___ TENSION

SPRING

Hot-wire ammeter,

hot-wire anemometer-An instrument that measures the velocity of wind or a gas by its cooling on an electrically heated wire. hot-wire instrument- 1. An electrothermic instmment operated by expansion of a wire heated by the current it is carrying. 2. A measuring device or transducer whose operation depends either on the expansion of a wire due to its being heated by an electric current or on the change in electrical resistance on the put of a wire that is heated or cooled. hot-wire microphone- A microphone in which the cooling or heating effect of a sound wave changes the resistance of a hot wire and thus the current through it.

hot-wire relay

- hum bars

hot-wire relay-A form of linear-expansion timedelay relay in which the longitudinal expansion of a wire, when heated, provides the mechanical motion to open or close contacts. The time required to heat the wire constitutes the delay. h o t wires-In an electrical system, those wires that carry the live current through the electrical system. Hot wires are usually black or red. hot-wire transducer -A unilateral transducer in which the cooling or heating effect of a sound wave changes the resistance of a hot wire and thus the current. house cables- Conductors inside a building used to connect communication equipment to outside lines. h o u s e k e e p i n g -In a computer routine, those operations, such as setting up constants and variables for use in the program, that contrihute directly to the proper operation of the computer but not to the solution of the problem. howl -An undesirable prolonged wail produced in a speaker by electric or acoustic feedback. howler- 1. An electromechanical device that produces an audio-frequency tone. 2. A unit by which the operator at a telephone test desk may apply a high tone of varying loudness to a line to call a subscriber’s attention to the fact that his or her receiver is off the hook. howling -System instability caused by acoustic feedback from loudspeaker to microphone. howl repeater-In the operation of telephone repeaters, a condition in which more energy is returned than is sent, with the result that an oscillation is set up on the circuit. h p -Abbreviation for horsepower. H-pad-An attenuation network in which the elements are arranged in the form of the letter H. h - p a r a m e t e r s -See hybrid parameters. h-particle -The positive hydrogen ion or proton resulting from bombardment of the hydrogen atom by alpha rays or fast-moving positive ions. HPF -Abbreviation for highest probable frequency. H-plane-The plane in which the magnetic field of an antenna lies. It is perpendicular to the E-plane. The principal H-plane of an antenna is the H-plane that also contains the direction of maximum radiation. H-plane bend-See H-bend. H-plane T-junction -Also called shunt T-junction. A wavelength T-junction in which the structure changes in the plane of the magnetic field. HRC -Abbreviation for horizontal redundancy checking. A validity-checking technique used on datatransmission blocks, in which redundant information is included with the information to be checked. H-scan -See H-display. HTL -Abbreviation for high-threshold logic. HTML -Abbreviation for Hypertext Markup Language. The coding language used to create hypertext documents for use on the World Wide Web. HTML allows a document to contain links to another document, giving WWW its hypertext capabilities. HTML page-A single file document written in HTML. Although this page may require multiple pages of paper if printed, it is typically viewed as a single scrolled page in a web browser. HTTP -Abbreviation for Hypertext Transfer Protocol. A cliendserver networking protocol for retrieving HTML documents on the World Wide Web. The client software application used in HTTP transactions is a web browser. hub- 1. On a control panel or plugboard, a socket or receptacle into which an electrical lead or plug wire may be connected for the purpose of carrying signals. 2. The narrow spindle around which the tape is wound on a reel

354 or in a cassette. 3. Local distribution center where signals from a master feed are relayed to other inputs. hue-1. Often used synonymously with the term color, but does not include gray. It is the dominant wavelength--.e., the one that distinguishes a color as red, yellow, etc. Varying saturations may have the same hue. 2. A more inclusive and more precise identification of the optical wavelengths than the commonly used word color. Rather than state that the maximum daylight sensitivity of the eye is to green-yellow or yellow-green, it is technically more rigorous to state that it occurs at a hue of 555 nanometers. 3. The perceptual term for that aspect of color described by words such as red, yellow, or blue. Achromatic colors, such as white, gray, and black, do not exhibit hue. 4. In color TV, one of the three characteristics of color. Defines color on the basis of its position in the frequency spectrum, i.e., whether red, blue, green, or yellow, etc. See also luminance; saturation. h u e control-on a color television receiver, the operating control that changes the hue (color) of the picture. hull potential -The voltage difference between a reference electrode and an immersed metallic hull, or the bonded underwater metallic appendages of a nonmetallic hull. h u m - 1. In audio-frequency systems, a low-pitched droning noise consisting of several harmonically related frequencies. It results from an alternating-current power supply, ripple from a direct-current power supply, or induction from exposure to a power system. By extension, the term is applied in visual systems to interference from similar sources. 2. A pattern produced on a facsimile record sheet when a signal at the power-line frequency or a harmonic of the power-line frequency is mixed with or modulates the facsimile signal. 3. A continuous lowfrequency interference caused by inadvertent pickup of 60-Hz or 120-Hz energy from nearby ac power sources. Most likely to originate in devices (like microphones) requiring substantial amplification. 4. A background tone caused by improper shielding of audio components or inadequate filtering of line voltage entering the equipment. 5. Electrical disturbance at the power supply frequency or harmonics thereof. h u m a n engineering-1. The science and art of developing machines for human use, giving consideration to the abilities, limitations, habits, and preferences of the human operator. 2. The determination of man’s capabilities and limitations as they relate to the equipment or systems he will use, and the application of this knowledge to the planning, design, and testing of man-machine combinations to obtain optimum performance, operability, reliability, efficiency, safety, and maintainability. 3. The study of the behavioral properties of humans in interaction with machines, and of total human-machine systems; the structuring of human-machine systems to enhance system performance. h u m a n f a c t o r s -A body of scientific facts about human characteristics. The term covers biomedical and psychosocial considerations in the areas of human engineering, personnel selection, training, life support, job performance aid, and human-performance evaluation. humanoid-Robot in the form of a person. hum-balancing pot -A potentiometer usually placed across the heater circuit. Its arm is grounded so that the heater voltage is balanced with respect to ground. h u m bar-A dark band extending across the picture. It is caused by excessive 60-Hz hum (or harmonics) in the signal applied to the picture-tube input. h u m bars -Relatively broad horizontal bars, alternately black and white, that extend over an entire TV picture. They may be stationary or may move up and

355 down. Sometimes referred to as a venetian-blind effect, they are caused by an approximate 60-Hz interfering fiequency or one of its harmonic frequencies. hum-bucking -The introduction of a small amount of voltage, at the power-line frequency, into a circuit to cancel unwanted power. hum-bucking coil-A coil wound around the field coil of a dynamic speaker and connected in series oppositioin with the voice coil. In this way, any hum ~oltageinduced in the field coil will be induced in the voice coil in the opposite direction and will buck, or cancel, the effects of the hum. humidity- 1. An indication of the water-vapor content of a gas mixture. 2. The amount of moisture in the air. Measured in percent relative humidity. umiclity transducer -A layer of hygroscopic isture-absorbing) substance deposited between two metal electrodes. These electrodes establish electrical contact with the hygroscopic chemical, which serves as a resistance element. Since the chemical coating tends to ;absorb moisture from the surrounding air, its resistance ilecreases as the humidity increases. In this manner, ]humidity vapiations are converted to resistance variations. h u m loop-A condition arising from the connection of two or more grounds to an amplifier system whereby circulating currents of low value at power-line frequency and harmonics are added to the program signals, causing lhum to appear in the background. umrriing --A sound produced by transformers hav:ing loose laminations or by magnetostriction effects in .iron core:;. 'The kequency of the sound is twice the powerline frequency. of an rf signal or h u m modulation-Modulation detected audio-frequency signal by hum. This type of hum -isheard only when the receiver is tuned to a station. hunting-1. Continuous, cyclical searching by a conlkol system for a desired or ideal value. Rapid hunting usually is termed oscillation; slower cycling is called bird(dogging. 2. Movements of a selector from terminal to .temnal until an idle one is found. V -Abbreviation for high voltage. -vector-A vector that represents the magnetic of an electromagnetic wave. In free space, it is perpendicular to the E-vector and the direction of propa-

-waive-A mode in which electromagnetic energy #canbe transmitted in a waveguide. An H-wave has an electric field perpendicular to the length of the waveguide, and a magnetic field parallel as well as perpendicular to the length. hybrid -1. An electronic circuit that contains both vacuum tubes and transistors. 2. A mixture of thinfilm and discrete integrated circuits. 3. A computer that has both analog and digital capabilities. 4. See hybrid junction. 5 . A transformer or combination of transformers or resistors that affords paths to three branches, A, €3, and C, so arr,anged that A can send to C, and B can receive from 6, hut A and B are effectively isolated. 6. A mixture or cornbiination of two different technologies. 7. Made up of several different components. 8. A telephone circuit that joins a two-wire line to a four-wire line. Originally, hybrids were transformers, but today they are electronic circuits. '3. In telecommunications, a circuit that divides a signal transmission channel into two channels (i.e., one for each direction) or, conversely, combines two channels into one. hybrid arrangement-On a telephone system, the use of hybrid-type transformers with carrier circuits or two-wire repeaters to amplify conversations in both directions without causing feedback or singing effects.

hum-bucking

- hybrid integrated circuit

hybrid balance-A measure of the degree of balance between two impedances connected to two conjugate sides of a hybrid set. Given by the formula for return loss. The better the balance, the greater is the transhybrid loss. hybrid circuit- 1. A circuit that combines the thinfilm and semiconductor technologies. Generally, the passive components are made by thin-film techniques. and the active components by semiconductor techniques. The active devices are attached to the thin-film passive components by a suitable bonding process. 2. Also called two-wire-four-wire terminating set. In telephone transmission circuits, a circuit for interconnecting two-wire and four-wire circuits through a differential balance or bridge circuit in which the two sides of the four-wire circuit form conjugate arms. 3. Any circuit made by using a combination of the following component manufacturing technologies: monolithic IC, thin film, thick film, and discrete component. 4. An integrated microelectronic circuit in which each component is fabricated on a separate chip or substrate, interconnected by means of iead wires so that each component can be independently optimized for performance. Example: a circuit package composed of transistor and diode dice, capacitor chips, and thick-film resistors and conductors. hybrid COil-AAlso called bridge transformer. 1. A single transformer that has, effectively, three windings and that is designed to be connected to four branches of a circuit so as to render these branches conjugate in pairs. 2. A four-winding transformer used at the junction between a two-wire and a four-wire circuit. It effectively separates the transmit and receive paths. 3. A hybrid consisting of a three-winding tapped transformer used with a balancing network to convert a fow-wire telephone line to a two-wire line. hybrid computer- 2 . A computer that results from the interconnection of an analog computer and a digital computer, plus conversion equipment, each contributing its special advantages to an assigned part of the solution of a class of complex problems. 2. A computer that combines both analog and digital equipment for purposes of solving problems that cannot be adequately or economically handled by either type of computer operating independently. The term does not denote the use of some analog equipment to preprocess data that is then converted to digital form and subsequently entered into a conventional digital computer. Rather, there is usually a continual flow of data in both directions between analog and digital equipment. 3. A computer for data processing in which both analog and discrete representations of data are used. 4. A computer designed with both digital and analog characteristics, combining the advantages of analog and digital computers when working as a system. hybrid electromagnetic wave -Abbreviated HEM wave. A wave in the electrornagnetic spectrum that has both electric and magnetic field vectors in the direction of propagation. hybrid electromechanical relay-A relay with isolated input and output in which electromechanical and electronic devices such as a solid-state amplifiers are combined to perform a switching function with an electromechanical output. hybrid integrated circuit -Abbreviated NIC. 1. An integrated circuit combining parts made by a number of techniques, such as diffused monolithic portions, thin-film elements, and discrete devices. 2. An arrangement consisting of one or more integrated circuits in combination with one or more discrete passive devices. Alternatively, the combination of more than one type of integrated circuit into a single integrated component. Hybrid ICs offer more circuit complexity than can be achieved with present-generation monolithic ICs. 3. A

hybrid junction - hyperbolic error composite of either monolithic integrated circuits or discrete semiconductor device circuits, in a unit-packaging configuration. 4. The physical realization of electronic circuits or subsystems from a number of extremely small circuit elements electrically and mechanically interconnected on a substrate. 4. The combination of thin-film or thick-film circuitry deposited on a substrate with chip transistors, capacitors, and other components. Thinfilm construction is used for microwave integrated circuits (MICs). hybrid junction -1. A transformer or waveguide circuit having four terminals (or four ports) so arranged that a signal entering at one terminal will divide and emerge from the two adjacent terminals but will be unable to reach the opposite terminal. Hybrid junctions (quadrature hybrids) are widely used in microwave circuits as power dividers and combiners (e. g., in balanced amplifiers, double-balanced mixers). 2. Also called hybrid tee or magic tee. A waveguide arrangement with four branches. When they are properly terminated, energy is transferred from any one branch into two of the remaining three branches. In common usage, this energy is divided equally between the two. 3. Any network or device that provides a low impedance path and impedance matching between adjacent circuits, but maintains a high degree of isolation between opposite circuits. Several types are common: (a) a three-winding hybrid transformer, (b) a resistance bridge circuit, and (c) a waveguide device known as a hybrid tee. hybrid loss- The transmission loss incurred when a signal goes through a hybrid coil. This loss is about 3.6 dB (3 dB because the current divides into two equal halves, and 0.6 dB for coil loss). hybrid microcircuit-A circuit produced by the combination of several different components in a single package. Hybrids form a middle ground between boards or modules using packaged components and monolithic ICs, which may not offer sufficient performance. Hybrids are commonly formed from a combination of chip or packaged active devices and thin- or thick-film passive devices. hybrid microelectronics-The entire body of electronic art that is connected with or applied to the realization of electronic systems using hybrid circuit technology. hybrid network -A nonhomogeneous communication network required to operate with signals of dissimilar characteristics (such as analog and digital modes). hybrid parameters-Also called h-parameters. The resultant parameters of an equivalent transistor circuit when the input current and output voltage are selected as independent variables. hybrid ring-Also called a rat race. A hybrid junction commonly used as an equal power divider. It consists of a reentrant line (waveguide) to which four side arms are connected. The line is of the proper electrical length to sustain standing waves. hybrids-A particular type of circuit or module consisting of a combination of two or more integrated circuits, or one integrated circuit and discrete elements. See hybrid integrated circuit. hybrid set-Two or more transformers interconnected to form a network having four pairs of accessible terminals. Four impedances may be connected to the four terminals, so that the branches containing them may be made conjugate in pairs. hybrid solid-state relay-A relay with isolated input and output in which electromechanical and electronic devices are combined to perform switching functions with a solid-state output. Typically, a reed switch is used to trigger a solid-state output device.

356

hybrid tee-See hybrid junction, 2. hybrid thin-film circuit-A microcircuit formed by attaching discrete components and semiconductor devices to networks of passive components and conductors that have been vacuum deposited on glazed ceramic, sapphire, or glass substrates. hybrid transformer-See hybrid coil. hybrid-type circuit-See hybrid integrated circuit; multichip circuit. hydraulic robot -Programmable machine that uses hydraulic motors and cylinders much as pneumatic robots use pneumonic motors and cylinders. In most cases these motors and cylinders are controlled by servo valves, a system that permits smooth motion as well as high lifting capacity. However, some hydraulic robots control their motors and cylinders with mechanical stops. hydroelectric-The production of electricity by water power. hydrogen electrode -A platinum electrode covered with platinum black, around which a stream of hydrogen is bubbled. The hydrogen electrode furnishes a standard against which other electrode potentials can be compared. hydrogen lamp-A special light source, used in some spectrophotometers, that produces invisible light energy. It is used in finding the light-energy frequency of test solutions. hydrogenthyratron-A thyratron containing hydrogen. hydrolysis-The chemical decomposition of a substance in the presence of water. Usually, it is considered in the sense of chemical degradation of insulating materials under the influence of heat or pressure and in contact with moisture (for example, hydrolysis of polyester films and coatings). hydromagnetics -See magnetohydrodynamicpower generator. hydromagnetic waves -Waves in which the energy oscillates between the magnetic field energy and kinetic energy of the hydrodynamic motion, the reservoirs being the self-inductance of the conductive matter and the mass inertia of the moving fluid. hydrometer -An instrument for determining the specific gravity of liquids, especially of a storage-battery electrolyte. It consists of a weighted glass float having a graduated stem that sinks into the liquid to a point determined by the specific gravity of the liquid. The float is usually contained in a glass, and a rubber syringe is used to withdraw a sample of the liquid. hydrophone-An electoacoustic transducer that responds to waterborne sound waves and delivers essentially equivalent electric waves. hydrostatic pressure -See static pressure. hygrometer -An instrument that measures the relative humidity of the atmosphere. hygroscopic-Readily capable of absorbing and retaining moisture from the atmosphere. The opposite term is nonhygroscopic. hygrostat-A device that closes a pair of contacts when the humidity reaches a prescribed level. hyperbola -1. A curve that is the locus of points having a constant difference of distance from two fixed points. 2. In hyperbolic guidance systems, a path along which the difference between the arrival times of pulses from two transmitters is constant. See also hyperbolic guidance system. hyperbolic error-The error in an interferometer system arising from the assumption that the directions of the wavefronts incident at two antennas of a base

hyperbolic grind - hysteresis

357 line are parallel, whereby the equiphase path is a cone. Mathematically the equiphase path is a hyperbola. hyperbolic grind-A shape of tape playback and record heads. It permits good head contact and better tesponse at high frequencies. hyperbolic guidance system -A method of guidance in which sets of ground stations transmit pulses ~TOIXIwhich a hyperbolic path can be derived to give range and course information for steering. See also hyperbola.

I

C b LAUNCH POINT

Hyperbolic guidance. hyperbolic head-A recording head whose polepiece surfaces (when viewed from the edge of the tape) .are shaped like the graph of a mathematical hyperbolic .Function. This shape offers a good compromise between -intimatetape contact at the gap and proximity to the tape 'of the rest of the pole-piece face (the latter is necessary for good low-frequency response). hyperbolic horn-A horn in which the equivalent tcross-seci:ional radius increases according to a hyperbolic law. hyperbolic navigation system -A method of .radionavigation (e.g., loran) in which pulses transmitted by two ground stations are received by an aircraft or ship. The difference in arrival time from each station is a measure of the difference in distance between the aircraft or ship and each station. This distance is plotted on one of many hyperbolic curves on a map. A second reading from another pair of stations (or from the same master and a different slave) establishes another point on a different hyperbolic curve. The intersection of the two curves gives the position o'f the aircraft or ship. hyperboloidal subreflector-The secondary reflector used in a Cassegrain antenna system. The surface has a hyperbolic shape. Hypercard-A software tool introduced by Apple computer in 1987 to provide new ways to organize, display. and navigate through data that broadened the capability of the Macintosh computer so noncomputer programmers could design and write their own computer applications.

hyperfocal distance-That object distance at which a camera must be focused so that the far depth of field just extends to infinity. The near limit of the depth of field is then half the hyperfocal distance. For normal photographic work this distance equals 1000 times the lens aperture diameter. hyperfrequency waves -Microwaves having wavelengths in the range from 1 centimeter to 1 meter. hyperlink-On a computer screen, a colored section of text (usually blue) that, when clicked. takes one to another web page. hypersensor-A single-component, reset-table circuit breaker that operates as a majority-carrier tunneling device. It is used to provide overcurrent or overvoltage protection of integrated circuits. hypersonic-Having five or more times the speed of sound. hypertext - 1. A concept for organizing information made possible by computers, in which keywords or phrases not only reference additional resources but also serve as software links to these resources. When viewing an HTML document with a browser, hypertext links or anchors are displayed (usually in blue) as underlined text. Clicking on this text immediately establishes a network connection to another file (or another place in the same file) containing more information on the underlined subject, and causes the browser to display this information. The other file can be anywhere on the Internet, and may contain almost anything including text, images, movies, or sounds. 2. A system that allows documents to be cross-linked in such a way that the reader can explore related documents by clicking on a highlighted word or symbol. 3. Generally, any text that contains links to other documents- words or phrases in the document that, when selected by a reader, cause another document to be retrieved and displayed. hyspersyn motor-A synchronous motor that combines the desirable features of the induction. hysteresis, and dc-excited synchronous motor, resulting in high efficiency and power factor. It possesses the vigorous starting torque of an induction motor, the synchronization torque of a hysteresis motor, and the stiffness of an externally dc-excited synchronous motor. hysteresigraph -A device for experimentally presenting or recording the hysteresis loop of a magnetic specimen. hysteresis- 1. A property of all magnetic materials that causes the value of magnetic flux density to lag behind the change in value of the magnetizing force that produces the flux. It is caused by the reluctance of the molecules to change their orientation. Work done to move the molecular magnets is a loss and appears in the form of heat. 2. A type of oscillator behavior in which multiple values of the output power and/or frequency correspond to given values of an operating parameter. 3. The temporary change in the counting rate-versus-voltage characteristic of a radiation-counter tube (caused by previous operation). 4. The difference between the response of a unit or system to an increasing and a decreasing signal. 5 . A form of nonlinearity in which the response of a circuit to a particular set of input conditions depends not only on the instantaneous values of those conditions, but also on the immediate past (recent history) of the input and output signal. Hysteretical behavior is characterized by inability to retrace exactly on the reverse swing a particular locus of input/output conditions. 6. The lag in the response of an instrument or process when a force acting on it changes abruptly. 7. The property of a magnetic material by virtue of which the magnetic induction for a given magnetizing force depends on the previous conditions of magnetization. 8. This term literally means to lag behind.

hysteresisbrake

- Hz

It is quite often used to describe the residual effect that remains after the primary effect has been removed, or the lag that exists between the responding parameter and the changing parameter. It can be seen in stress-strain and magnetizing-force magnetic-field relationships. 9. A tendency for a display element to stay in either the on or off condition once it has been switched. With hysteresis, for example, a sustaining voltage can be applied to a display to keep all lighted pixels glowing without lighting any that are supposed to be off. hysteresis brake -See hysteresis clutch. hysteresis clutch -Also called hysteresis brake. A proportional torque-control device that employs the hysteresis effect in a permanent-magnet rotor to develop its output torque. It is capable of synchronous driving or continuous slip, provided heat can be removed, with almost no torque variation at any slip differential. Its control-power requirement is small enough for vacuumtube or transistorized drive. hysteresiscope -An instrument used to obtain hysteresis loops on a cathode-ray oscilloscope screen without the need for specially prepared ring samples. It is used in the inspection of magnetic material. hysteresis cunre-1. A curve showing the relationship between a magnetizing force and the resultant magnetic flux. 2. A graph showing the amount of magnetism imparted to a magnetizable material as the result of a varying magnetic field. This coincides with the variations of the applied field only through a relatively narrow range between zero magnetism and saturation, but the addition of a bias allows an audio signal to be recorded on a magnetic tape within this linear range, for minimum distortion. hysteresis distortion-Distortion of waveforms in circuits containing magnetic components. It is due to the hysteresis of the magnetic cores. hysteresis error -The difference in the reading obtained on a measuring instrument containing iron when the current is increased to a definite value and when the current is reduced from a higher value to the same definite value. hysteresis heater -An induction device in which a charge (or a muffle around the charge) is heated by hysteresis losses due to the magnetic flux produced in the charge. hysteresis loop-1. A curve (usually with rectangular coordinates) that shows, for a magnetic material in a cyclically magnetized condition, two values of the magnetic induction for each value of the magnetizing force: one when the magnetizing force is increasing, the other when it is decreasing. 2. The graphical representation of

358 +B I (GAUSSES)

-B

Hysteresis loop.

relationship between the magnetizing force and the resultant induced magnetization of a ferromagnetic material when the magnetizing field is carried through a complete cycle of equal and opposite values under cyclic conditions. hysteresis loss- 1. The power expended in a magnetic material as a result of magnetic hysteresis. 2. The power dissipated in a ferromagnetic core as a result of its hysteresis; proportional to the product of the area of the loop, times the frequency, times the volume of the core. 3. Loss that occurs when a rapidly changing current, such as ac, is forced to continually supply energy to an iron core that tends to “memorize” previous magnetic states. 4. The power loss in a magnetic core, such as in a transformer energized by an alternating current, that is due to hysteresis. hysteresis meter -An instrument for determining the hysteresis loss in a ferromagnetic material. It measures the torque produced when the test specimen is placed in a rotating magnetic field or is rotated in a stationary magnetic field. hysteresis motor-A synchronous motor without salient poles or direct-current excitation. It is started by the hysteresis losses induced in its secondary by the revolving field. hystoroscope -An instrument used to observe, measure, and record the magnetic characteristics of both easy and hard axes of magnetic materials. Hz-Letter symbol for hertz, meaning cycles per second (of any periodic phenomenon).

I

I- 1. Sym00l for current. 2. Abbreviation for lumnous intensity. IACS-Abbreviation for International Annealed Copper Standard. A standard of copper conductivity by specifying resistivity and temperature. IBM card-A type of paper card that may have information recorded on it by means of punched holes and that may be read by a computer. IC- 1. Abbreviation for integrated circuit. 2. Abbreviation for internal connection. l c ~ -The o reverse current that occnrs when a specific dc voltage is applied in the nonconducting direction to the collector junction of a transistor while the emitter is open-circuited. ICE- Abbreviation for in-circuit emulator and incircuit emulation. ice loading-The weight of ice an antenna can accumulate without being damaged. icon --A small picture displayed on a computer screen that represents a command or an object that can be inanipulated by the user. Usually, the picture shows what the icon does. For example, the PRINT icon generally looks like a printer. iconoscope-A camera tube in which a beam of high-velocity electrons scans a photoemissive mosaic capable of storing an electrical charge pattern. IC s o c k e t -Female contact that provides pluggable electrical engagement on its inner surface for integrated circuit components to achieve interfacing to a printed circuit board. ICW -'4bbreviation for interrupted continuous wave. ID -Abbreviation for inside diameter. ideal bunching-A theoretical condition in which bunching of the electrons in a velocity-modulated tube .would give an infinitely large current peak during each #cycle. ideal capacitor-A capacitor having a singlevalued transferred-charge characteristic. ideal CryStal - A crystal having no mosaic structure and capable of X-ray reflection in accordance with the Darwin-Ewald-Prins law. ideal dielectric-A dielectric in which all the (energy required to establish an electric field in the dielecibic is returned to the source when the field is removed. i(A perfect dielectric must have zero conductivity. Also, ,all absorption phenomena must be lacking. A vacuum is ithe only known perfect dielectric.) ideal filter-Any filter in which the range of frelquencies within a chosen radius suffers no attenuation and the range of frequencies outside the radius is entirely attenuated. ideal-noise diode-A diode that has an infinite internal impedance and in which the current exhibits full shot-noise hctuations.

ideal transducer-Theoretically, any linear passive transducer that-if it dissipated no energy and, when connected to a source and load, presented its combined impedance to each -would transfer maximum power from source to load. ideal transformer -A hypothetical transformer that would neither store nor dissipate energy. Its selfinductances would have a finite ratio and unity coefficient of coupling, and its self- and mutual impedances would be pure inductances of infinitely great value. I demodulator -A demodulator circuit whose inputs are the chrominance signal and the signal from the local 3.58-MHz oscillator. The output of this demodulator is a video signal representing color in the televised scene. The Q demodulator is similar except that its input from the local oscillator is shifted 90". identification - 1. In radar, determining the identity of a displayed target (Le., which one of the blips in the display represents the target). 2. In a computer, a code number or code name that uniquely identifies a record, block, file, or other unit of information. identification beacon -A code beacon used for positively identifying a particular point on the earth's surface. identification,friend or foe- Abbreviated IFF. A system using radar transmissions to which equipment carried by friendly forces automatically responds, for example, by emitting pulses, thereby distinguishing themselves from enemy forces. It is the primary method of determining the friendly or unfriendly character of aircraft and ships by other aircraft or ships and by ground forces employing radar-detection equipment and associated IFF units. identifier -1. A symbol whose purpose is to identify, indicate, or name a body of data. 2. A mnemonic code used to identify or name an item of data or data format in a computer. identify-In a computer, to attach a unique code or code name to a specific unit of information. idiochromatic-Having photoelectric properties characteristic of the pure crystal itself and not due to foreign matter. I-display-In radar, a display in which a target appears as a circle when the radar antenna is pointed directly at it. The radius of the circle is proportionate to the target distance. When the antenna is not pointing at the target, only a segment of the circle appears. Its length is inversely proportional to the magnitude of the pointing error, and the segment points away from the direction of error. idle c h a r a c t e r s -Control characters interchanged by a synchronized transmitter and receiver to maintain synchronization during a nondata period. idle noise- 1. Noise that exists in a communication system when no signals - are present. 2. Unwanted, random 359

idler - ignitor firing time electrical energy present in a transmission system under unmodulated conditions. idler- 1. A rubber-tired wheel that transfers power from a phonograph motor to the turntable rim. 2. An intermediate drive wheel, usually with a rubber or neoprene “tire?”that transfers rotational energy from a driven wheel to a third wheel. Often used for speed reduction between a drive motor and capstan shaft. See also pinch roller. idler drive-1. A drive system used to rotate a turntable, which consists of a drive-shaft that is turned by the motor pulley and that drives the inside rim of the turntable platter. 2. A system for transferring power from a motor to a turntable through a rubber wheel that contacts the motor shaft and the inside rim of the platter. idler frequency-A sum or difference frequency, other than the input, output, or pump frequencies, generated within a parametric device and requiring specific circuit consideration to achieve the desired performance of the device. idler pulley-A pulley used only for tightening a belt or changing its direction. The shaft does not drive any other part. idle time-That portion of available time during which the hardware is not in use. idle-trunk lamp-A signal lamp that indicates that the outgoing trunk with which it is associated is not busy. idling current -Also called quiescent current. The zero-signal power supply current drawn by a circuit or by a complete amplifier. IDT -Abbreviation for interdigital transducer. IEC-1. Abbreviation for integrated electronic component. 2. Abbreviation for International Electrotechnical Commission. An organization that cooperates with the IS0 for technology standards. IEEE- Abbreviation for Institute of Electrical and Electronic Engineers. A professional organization of scientists and engineers whose purpose is the advancement of electrical engineering, electronics, and allied branches of engineering and science. (The IEEE resulted from the merger of the IRE and the AIEE.) IEEE-488 bus-Also known as the general-purpose interface bus (GPIB). 1. An interface standard that defines digital data exchange between up to 15 instruments; a bus widely used to connect test instrumentation. 2. An industry-standard bus that defines a digital interface for programmable instrumentation; it uses a byte-serial, bit-parallel technique to handle 8-bit-wide data words. Published by the IEEE in 1975, revised 1978. IEM -Abbreviation for illuminated entry module. An electronic convenience control (offered by Ford Motor and General Motors) that lights up a car’s interior and door keyhole slots for a timed interval of about 20 seconds while the car owner unlocks the door. IF -Abbreviation for intermediate frequency. IF amplifier -See intermediate-frequency amplifier. IF bandwidth -The range of frequencies centered about the intermediate frequency limited by the -3-dB amplitude points. IF canceler -In radar, a moving-target-indicator canceler operating at intermediate frequencies. IFF-See identification, friend or foe. IF rejection -The ability of a superheterodyne AM or FM tuner’s IF circuits to reject external interference at the intermediate frequency. Measured in decibels (the higher the better), it is of more significance in AM than in FM reception because the lowest broadcast AM frequency, now 530 kHz, is so close to the standard AM intermediate frequency of 455 kHz. IFRU -See interference-rejection unit. IF selectivity-The ability of the IF stages of a superheterodyne receiver to accept the signal from one

360 station while rejecting the signal of the adjacent stations; it is the ratio of desired to undesired signal required for 30-dB suppression of the undesired signal (IHF standard). if statement -See conditional statement. IF strip- See intermediate-frequency strip. IF transformer -See intermediate-frequency transformer. IGFET -Abbreviation for insulated-gate field-effect transistor. Though a less popular term than MOS (metaloxide semiconductor), it more precisely defines devices made by various MOS processes. See also metal-oxide semiconductor field-effect transistor. ignition c a b l e -Cable designed primarily for automotive ignition systems. ignition coil-1. An iron-core transformer that converts a low direct voltage to the 20,000 volts or so required to produce an ignition spark in gasoline engines. It has an open core, a heavy primary winding connected to the battery or other source through a vibrating armature contact, and a s e c o n d q winding with many turns of fine wire. 2. That part of the ignition system which acts as a transformer to step up the battery voltage to many thousands of volts. The high-voltage surge then produces a spark at the spark-plug gap.

PRIMARY TERMINAL

HV OUTPUT

SECONDARY PRIMARY SECONDARY GROUNO WlNOlNG WINDING

COMPOUND INSULATION

CASE

TERMINAL

Ignition coil.

ignition control -Control of the instant that static current begins to flow in the anode circuit of a gas tube. ignition interference -Noise produced by sparks or other ignition discharges in a car, motor, or furnace ignition, or by equipment with loose contacts or connections. ignition reserve-In a gasoline engine, the difference between the available voltage and the required ignition voltage. ignition s y s t e m -In an automobile, the system that furnishes high-voltage sparks to the engine cylinders to fire the compressed air-fuel charges. It consists of battery, ignition coil, ignition distributor, ignition switch, wiring, and spark plugs. ignition terminal -Solderless terminal designed for use in automotive ignition work. ignition voltage-In a gasoline engine, the peak voltage required to produce a spark across the plug electrodes. ignitor discharge-In switching tubes, a dc glow discharge between the ignitor electrode and a suitably located electrode. It is used to facilitate radio-frequency ionization. ignitor electrode- An electrode (which is partly immersed in the mercury-pool cathode of an ignitron) used to initiate conduction at the desired points in each cycle. ignitor firing time-In switching tubes, the interval between application of a dc voltage to the ignitor electrode and start of current flow.

ignitor interaction

361

ignitoir interaction-In a tr, pre-tr, or attenuator tube, the difference between the insertion loss measured at a specified level of ignitor current and that measured at zero ignitor current. ignitoir l e a k a g e resistance-In a switching tube, the insulation resistance measured between the ignitor electrode terminal and the adjacent rf electrode in the absence ad an ignitor discharge. ignitor oscillation --A relaxation type of oscillation in the ignitor circuit of a tr, pre-tr, or attenuator tube. ignitoir voltage drop-In switching tubes, the dc voltage between the cathode and anode at a specified ignitor current. ignitron -A type of mercury-pool rectifier that has only one anode. The arc is started for each cycle of operation by an ignitor that dips into the mercury pool. The mercury pool serves as the cathode of the rectifier. The ignitron is characterized by the ability to withstand tube currents several times as high as rated values for a Sew cycles.

CClNNECTlOPl

Ignitron.

ignore -In a computer, a character code indicating that no action is to be taken. IGY -Abbreviation for international geophysical year. IHFM -Abbreviation for Institute of High-Fidelity Manufacturers, an association of manufacturers that publishes ratiings and standards for high-fidelity equipment. 1*L -Abbreviation for integrated injection logic (pronounced “I-squared L”). 1. A bipolar logic circuit that bas a much higher packing density than conventional bransistor-transistor logic or complementary metal-oxide semiconductor (CMOS), dissipates low power, and has high-speed characteristics. To an extent it combines bipolar speed, MQS circuit density, and the low-power dissipation of CMOS. 13L@-Abbreviation for isoplanar integrated injection logic (Fairchild Camera & Instrument Corp.). illegal character-A character or combination of bsits that does not have validity according to some criterion; for example, a character that is not a member osf a specified alphabet. illegal operation -An impossible-to-execute computer instmction. i h m i n a n c e - 1 . The density of luminous flux at a given distance from the center of a source. It is equal to the total flux divided by the surface area over which iii is uniformly spread. The units of illuminance are

- image converter

lumenskm’, lumens/ft2, etc. One lumedft’ is the same as a footcandle; one lumen/cm2 is the same as one phot; and one lumedm’ is equal to one lux, or one meter-candle. 2. Luminous flux incident per unit area of a surface; luminous incidence. (The use of the term illumination for this quantity conflicts with its more general meaning.) illuminant-C -The reference white of color television-ie., light that most nearly matches average daylight. illuminate-1. To expose to light, 2. In radar. to strike with a radar signal so that reflection returns the signal to the source for interpretation. illuminated -Characteristic of a surface or object that has luminous flux incident on it. illuminated entry module-See IEM. illumination-1. The light flux incident on a unit projected area; it is the photometric counterpart of irradiance and is expressed in footcandles. 2. The density of the luminous flux incident on a surface; it is the quotient of the luminous flux by the area of the surface, when the latter is unifomdy illuminated (SI unit = lux or lx). 3. The general term meaning the application of light to a subject. Should not be used in place of the specific quantity illuminance. illumination control-A photorelay circuit that turns on artificial lighting when nahxal illumination decreases below a predetermined level. illumination sensitivity-The output current of a photosensitive device divided by the incident illumination at constant electrode voltages. illuminometer -A photometric instrument used to measure the illumination falling on a surface. May be photoelectric or visual. ILO -See injection-locked oscillator. ILS-Abbreviation for instrument landing system. A radio beacon system forming a straight pencil beam from the runway that planes can follow from 5 to 7 miles (8 to 12 kilometers) away. An alternative is a microwave landing system. image - 1. The instantaneous illusion of a picture on a flat surface. 2. The unused one of the two groups of sidebands generated in amplitude modulation. 3. A spatial distribution of some physical property (e.g., radiation, electric charge, conductivity, or reflectivity) made to correspond with another distribution of the same or another physical property. 4. A two-dimensional representation of an object or a scene formed by creating a pattern from the light received from the scene. image admittance -Reciprocal of image irnpedance. image antenna-The imaginary counterpart of an actual antenna. For mathematical purposes it is assumed to be located below the ground and symmetrical with the actual antenna. image-attenuation constant-The real part of the transfer constant. i m a g e c o m p r e s s i o n -The translation of data in any format (such as video or graphics) to a more compact form for storage or transmission such that it takes up less space in a computer’s memory. image converter- 1. A solid-state optoelectric device capable of changing the spectral characteristics of a radiant image. Examples of such changes are infraredto-visible and X-ray-to-visible. 2. An electron tube that employs electromagnetic radiation to produce a visual replica of an image produced on its cathode. Electrons ejected from the photosensitive cathode by the incident radiation are accelerated to and focused upon a fluorescent phosphor screen, thus forming the visual replica. Image converters can be used in the infrared, ultraviolet, and

image-converter tube

- image plane holography

X-ray regions as well as in the visible. An example of an infrared-sensitive image converter is the snooperscope. image-converter tube -See image tube. image dissection -An optical, mechanical, or electronic process, or a combination of such processes, in which an optical image is divided into discrete segments prior to being photographed, recorded, transmitted, or processed in some other way. image dissector-1. A television camera tube in which the image is swept past an aperture in a series of 525 interlaced lines 30 times per second. Instead of a beam scanning the image, the entire image is scanned past the aperture, which “dissects” the image -hence the name. See also dissector tube. 2. In OCR, a mechanical or electronic transducer that detects in sequence the light levels in different areas of a completely illuminated sample space.

PHOTOSENSITIVE DEFLECTION FOCUSING CATHODE COIL COIL

ANOD~ (WALL COATING)

APERTURE

MULTiPLlER HOUSING

SEG‘MENTS

WINOOW

Image dissector, 1.

image dissector tube-An electron tube that is used as a camera tube for a television system. When the picture to be transmitted is focused on a photosensitive surface, electrons are emitted from each section of the surface in proportion to the amount of light in that certain part of the picture, and are then drawn down the tube in a positive anode. However, the electrons are still focused in an electric field. The focusing fields are changed regularly to sweep the electron picture horizontally and vertically as it travels down the tube. The picture then passes through an aperture into an electron multiplier, where the output of the multiplier varies with the different parts of the picture. This output represents the dissecting of the picture into ordered parts. image distortion -Failure of the reproduced image in a television receiver to resemble the original scene scanned by the camera. image effect -An effect produced on the field of an antenna as the electromagnetic waves are reflected from the earth’s surface. image e n h a n c e m e n t -Also called detail enhancement. The process by which the image is manipulated to increase the information extracted by the human visual system. image-enhancing equipment-An elaborate device, often involving a computer, in which a photograph is scanned by a point of light, the amplitude of the electrical signal being modified electronically before being rerecorded on another film. image fOrCe-The force on a charge due to that charge or polarization which it induces on neighboring conductors or dielectrics. image frequency- 1. In heterodyne frequency converters, an undesired input frequency capable of producing the selected frequency by selecting one of the two sidebands produced by beating. The word image implies the mirrorlike symmetry of signal and image frequencies about the beating oscillator frequency or intermediate

362 frequency, whichever is higher. 2. An undesired signal obtained in frequency conversion using a mixing or heterodyning process. image-frequency rejection ratio -Of a superheterodyne receiver, the ratio of the response at the desired frequency to the response at the image frequency. image iconoscope- 1. An iconoscope in which greater sensitivity is obtained by separating the function of charge storage from that of photoelectric emission. An optical image is projected on a continuous photosensitive screen, and the electron emission from the back of this screen is focused electromagnetically onto a mosaic screen that is scanned by an electron beam as the original emitron cathode-ray tube. The British term is super-emitron. 2. A camera tube similar in design to the iconoscope. However, the image formed in the image iconoscope is projected on a photocathode that emits photoelectrons to be focused on a material, forming the charge image. image impedance -The impedances that will simultaneously terminate all inputs and outputs of a transducer so that at each of its input and outputs the impedances in both directions are equal. image intensifier-1. A system for increasing the sensor response to a radiation pattern or image by interposing active elements between the sensor and the image, and supplying power to the active element. This is normally done by focusing the scene to be imaged on the photocathode of the tube, giving rise to a photoelectron pattern corresponding to the optical image. This pattern is accelerated and focused onto a phosphor, which emits light to reproduce a visual image of the scene. 2. Device used in X-ray techniques for brightening the fluoroscopic image several hundred times and reducing radiation exposure. 3. An electronic tube equipped with a lightsensitive electron emitter at one end and a phosphor screen at the other end; an electron lens inside the tube relays the image. This device is used in astronomy and in military and surveillance systems to provide night vision. image interference-In a receiver, a response due to signals of a frequency removed from the desired signal by twice the intermediate frequency. image-interference ratio -In a superheterodyne receiver, the effectiveness of the preselector in rejecting signals at the image frequency. image inverter-A fiber-optic device that rotates an image through a predetermined angle. image orthicon-1. A camera tube in which a photoemitting surface produces an electronic image and focuses it on one side of a separate storage target. The opposite side of the target is then scanned by low-velocity electrons to produce the output. 2. A camera tube widely used in TV broadcasting. It consists of three sections all included in a single vacuum envelope. The three parts are as follows: (a) A photosensitive film sometimes called the photocathode. The scene to be televised is focused on this film by an outside camera lens. (b) The scanning beam provided by an electron gun, which scans lines of the target film. The gun’s beam is deflected by electromagnets within the tube (the whole picture is scanned by the beam in 1/30 of a second). ( c ) A return beam of electrons falls on a multiplier section, where an electron current of sufficient magnitude is developed to be sent out from the broadcast transmitter as a video signal. See Figure on p. 367. i m a g e p h a s e constant-The imaginary part of the transfer constant. image plane holography-A type of holographic process in which a lens is used to image the subject in the film plane.

image ratio - immersion plating

363 ELECTRON GUN

II \\

Ii

I

ALIGNMENT COIL

'\,

FOCUSING COIL

DEFLECTION COILS

TARGET

TARGET SCREEN

ELECTRON IMAGE

PHOTO CATHODE

'\

'

\ F I ~ T H SIGNAL PLATE DYNODE (OUTPUT)

'FIRST GRID 3 DYNODE (MULTIPLIER FOCUS)

GRID 4 (BEAM FOCUS)

GRID 5 (DECELERATOR)

GRID'6 (IMAGE ACCELERATOR)

Image orthicon.

image ratio--In

a heterodyne receiver, the ratio of

ihe image-frequency signal input to the desired signal

.input for identical amplitude outputs. image redundancy -The multiple storage of a :single image. image rejection-1. The suppression of image.Frequency signals in a superheterodyne receiver. 2. The rejection by the tuner of a signal at the image (secondchannel) frequency, corresponding to the tuned (real) frequency plus twice the intermediate frequency when the liocal oscillator is working above the signal frequency, or minus twice the intermediate frequency when the local oscillztor is working below the signal frequency. 3. The ability of a superheterodyne receiver to ignore :signals removed from the desired frequency by twice the intermediate frequency (10.7 MHz in home FM receivers, 455 kHz in home AM receivers). Image response can be reduced by using selective tuned stages in the input circuits of the tuner. As with most tuner rejection or suppression specifications, it is measured in decibels, with higher numbers indicating more suppression. image-rejection ratio -The ratio (in decibels) of the signal required for a 30-dB signal-to-noise ratio to that required for the same ratio but at the image frequency. An increase in front-end selectivity increases the ratio. image-reject mixer-A combination of two balanced mixers and associated hybrid circuits designed for separation of the image channel from the signal channels normally present in a conventional mixer. The arrangement makes possible image rejection of up to 30 dB without the use of filters. image response-The response of a heterodyne receiver to a signal that is separated by twice the intermediate frequency from the frequency to which the receiver is tuned. Unless there is some preselection, images will cause spurious unwanted responses when the spectrum occupied by a signal is greater than twice the frequency of the first IF stage of the receiver. image retaining panel-A type of electroluminescent display that records and maintains an irradiated image on its phosphor screen, provided a dc potential is applied to the screen. Used to record X-ray images, the display can retain an image for up to 30 minutes if the dc potential ns maintained. image retention-The vidicon pickup tube's tendency to retain an image on its target area after it has stopped scanning that image. Extreme image retention results in the image being burned into the target area.

image storage panel-A modified form of an image retaining panel that can be used in subdued daylight. This is achieved by the addition of a layer of zinc oxide between the panel's phosphor layer and its rear electrode. The zinc oxide cannot be made photoconductive by low-intensity daylight, but does become so when exposed to X-rays. An electroluminescent image is obtained by the application of ac voltage to the panel following its exposure to the X-rays. image transducer- Any arrangement of a bundle of optical fibers that alters the shape of the image. For example, by a systematic regulation of the spacing of the fibers from the entrance end to the exit end, a distortion of the image can occur that may be used to neutralize or compensate for the distortion introduced by the lens, prism, or mirror components in an optical system. image-transfer constant -See transfer constant. image tube -Also called an image-converter tube. An electron tube that reproduces on its fluorescent screen an image of an irradiation pattern incident on its photosensitive surface. image-tube camera-A camera system in which the image formed on the fluorescent screen of an image converter tube in the system is recorded by photography, or direct-contact printing from the face of the tube. imaging -The process of creating and manipulating data for visual presentation and storage. imbedded layer- A conductor layer deposited between insulating layers. IMD -See intermodulation distortion. imitative deception-The transmission of messages in the enemy's communication channels for the purpose of deceiving him or her. immediate access-The ability of a computer to put data in storage or remove it from storage without delay. immediate-access store -A store whose access time is negligible compared with other operating times. immediate addressing - 1. In a computer, a mode of addressing in which the operand contains the value to be operated on, and no address reference is required. 2. An addressing mode in which the data for an instruction is the next sequential byte in the instruction stream. immediate data --Data that immediately follows an instruction in a memory and is used as an operand by that instruction. immersion plating - 1. A method of metal deposition that depends on a galvanic displacement of the metal

immersion pyrometer

- impedance bridge

being plated by the substrate. Thickness of the plating is limited to 10 to 50 microinches (0.254to 1.27 km). 2. The chemical deposition of a thin metallic coating over certain base metals by a partial displacement of the base metal. immersion pyrometer-An instrument for determining molten-steel temperature and normally consisting of a platinum-platinum rhodium bimetal thermocouple junction and a recording device for transposing the millivoltage into degrees of temperature. immittance-A term that denotes both impedance and admittance. It is commonly applied to transmission lines, networks, and certain kinds of measuring instruments. IMOS- See ion-implanted MOS. impact excitation-The starting of damped oscillations by a sudden surge, such as by a spark discharge. impact modulator amplifier-A fluidic device in which the impact plane position of two opposed streams is controlled to alter the output. impact predictor-A device that can determine, in real time, the point on the earth’s surface where a ballistic missile will impact if thrust is instantaneously terminated. impact printer-1. Any type of printer that generates characters by using some form of stamping or inking through a ribbon by some sort of character slug, element, or hammer-needle. (Daisy-wheel printers are impact printers.) 2. Any mechanical imprinting device that forms characters by striking characters against a ribbon onto paper. 3. A mechanical printer operating at relatively low speeds-from 150 lines per minute to 1800 lines per minute. Has multiple copy capability and normally is capable of producing an original plus three copies. Impact printers are identified as letter-quality, dot-matrix, and line-printing types. No longer in common use.

ER

RIBBON CONTAINED

Impact printer (dot-matrix).

impact printing -Printing that is produced by the impact of a key on an inked ribbon, transferring the impression of a character onto the paper located behind the ribbon. impact resistance-Resistance to fracture under shock force. IMPATT- Acronym for impact avalanche and transit time. IMPATT diode -Impact avalanche and transmit time diode. 1. A pn-junction diode operated with heavy back bias so that avalanche breakdown occurs in the active region. To prevent burnout, the device is so

364 constructed that the active region is very close to a good heat sink. For the same reason, the bias supply must be a constant-current type. 2. A device whose negative resistance characteristic is produced by a combination of impact avalanche breakdown and charge-carrier transittime effects. Avalanche breakdown occurs when the electric field across the diode is high enough for the charge carriers (holes or electrons) to create electron-hole pairs. With the diode mounted in an appropriate cavity, the field patterns and drift distance permit microwave oscillations or amplification. 3. A semiconductor microwave diode that, when its junction is biased onto avalanche, exhibits a negative resistance over a frequency range determined by the transit time of charge carriers through the depletion region.

IMPATT diode.

IMPAlT oscillator-An oscillator in which the active element is an IMPATT diode operating in a negative resistance mode. Dc to rf conversion efficiencies are normally less than 20 percent. Present devices operate above 5 GHz. impedance- 1. The total opposition (i.e., resistance and reactance) a circuit offers to the flow of alternating current at a given frequency; the ratio of the potential difference across a circuit or element of a circuit to the current through the circuit or element. It is measured in ohms, and its reciprocal is called admittance. Symbol: Z . 2. The combination of resistance and reactance 3. Combined opposition to current resulting from resistance, capacitance, and inductance. 4. The sinusoidal terminal voltage of a circuit divided by the current through it. 5. A speaker’s resistance to an alternating current, which varies with frequency. A speaker’s rated impedance is usually the value measured at 400 Hz. 6. The opposition to alternating current in a circuit, generally categorized as either high or low, and measured in ohms. 7. The total opposition that a circuit offers to the flow of alternating current or any other varying current at a particular frequency. It is a combination of resistance, R, and reactance, X , measured in ohms. impedance angle- Angle of the impedance vector with respect to the resistance vector. Represents the phase angle between voltage and current. impedance at the intermediate frequency-In a mixer semiconductor diode, the impedance measured at the output terminals of a mixer circuit when the device is driven by a local oscillator under specified conditions. impedance bridge-A device for measuring the combined resistance and reactance of a component part of a circuit.

365

impedance characteristic-A graph of impedance ve:rsus frequency of a circuit or component. impedance coil -A coil whose inductive reactance is used to hinder the flow of alternating current in or between circuits. impedance compensator- 1. An electric network used with a line or another network to give the impedance of the combination a certain characteristic over a desired frequency range. 2. A circuit that ensures that a transmission line is a proper electrical load for its communicating devices. It is connected in parallel with the devices. impedance coupling-A method of coupling using an impedance as the coupling device common to both the primary and secondary circuits. This type of coupling is usually 1.imited to audio systems, where high gain and limited bartdpass are required. impedance drop-The vector sum of the resistance drop and the reactance drop. (For transformers, the resistance 'drop, the reactance drop, and the impedance drop are, respectively. the sum of the primary and secondary drops reduced to the same terms. They are usually expressed in percent of the secondary-terminal vohge.) impedance ground- An earth connection made through an impedance of predetermined value usually 'chosen to limit the current of a short-circuit to ground. impedance irregularities -Breaks or abrupt changes that occur in an impedance-frequency curve when unlike sections of a transmission line are joined together Nor when ith'ere are irregularities on the line. impedance match-The condition in which the impedance of a component or circuit is equal to the internal iimpedance of the source or the surge impedance (of a transmission line, thereby giving maximum transfer (of energy from sources to load, minimum reflection, and :minimum,distortion. impedance matching - 1. The connection across a :sourceimpedance of another impedance having the same :magnitudeand phase angle. If the source is a transmission :line, reflection is thereby avoided. 2. The process of adjusting the impedances of a load and of its power source so that they are equal. This permits the greatest ]possibletransfer of power. 3. Making the impedance of a itemhating device equal to the impedance of the circuit to .which it is connected in order to achieve optimum signal ikansfer. impedance-matching transformer-A transformer used to match the impedance of a source and load. ~ ~ p e c i ~plethysmograph ~ce -An instrument used to detect the increased blood volume in the tissues of the body during a contraction of the heart. See also electrical-impedance cephalography; finger plethysmograph. impedance transformer-A transformer that transfers maximum energy from one circuit to another. impedance triangle-A diagram consisting of a right triangle. The sides are proportional to the resistance and reactance in an ac circuit, with the hypotenuse representing the impedance. imperfect dielectric-A dielectric in which part of the energy required to establish its electric field is converted into heat instead of being returned to the electric system when the field is removed. imperfection --In a crystalline solid, any deviation in structure from an ideal crystal (one that is perfectly periodic in structure and contains no foreign atoms). implantable p a c e m a k e r -A miniature pulse generator surgically implanted beneath the skin and provided with output leads that connect directly to the heart muscle. The electrodes may contact either the outer wall of the

impedance characteristic - impulse excitation heart muscle (myocardial electrodes) or the inner surface of the heart chamber (endocardiac electrodes). implied AND- Also called dot AND or wired AND. A logic element in which the combined outputs are true if and only if all outputs are true. (Sometimes improperly called dot OR or wired OR.) implied OR -Also called wired OR. A logic element in which the combined outputs are true if one or more of the outputs are true. implode-The inward bursting of a picture tube due to its high vacuum. import-To copy data created by one computer program or file into another. impregnant - 1. A substance, usually a liquid, used to saturate the paper dielectric of a capacitor and replace the air between its fibers, thereby increasing the dielectric strength and the dielectric constant of the capacitor. 2. A substance intended to replace the air as dielectric between the electrodes of a capacitor. impregnate- 1. To fill voids and air spaces (of a capacitor or transformer) with a material having good insulating properties commonly called an impregnant. 2. To fill the voids and interstices of a material with a compound. This does not imply complete fill or complete coating of the surfaces by a hole-free film. impregnated coils-Coils that have been penneated with an electric grade varnish or other protective material to protect them from mechanized vibration, handling, fungus, and moisture. impregnating -Complete filling of even the smallest voids in a component or closely packed assembly of parts. Low-viscosity compounds, usually liquids, are used. The process is frequently accomplished by a vacuum- process in which all air is removed before introducing the impregnating material. Typical examples of impregnating are the filling of capacitors or transformer windings. impregnation -1. The process of coating the insides of coils and closely packed electronic assemblies by dipping them into a liquid and letting it solidify. 2. The process of completely filling all interstices or a part or assembly with a thin. liquid, electrically insulating material. The process is best accomplished by first removing all air (creating a vacuum), then introducing the impregnant, and finally applying atmospheric or elevated pressures to completely force-fill the system. impressed voltage-The voltage applied to a circuit or device. improvement threshold -A characteristic of FM radio receivers that determines the minimum rf signal power required to overcome the inherent thermal noise. For increasing values of rf power above th~spoint, an improvement of signal-to-noise ratio is obtained. impulse-1. A pulse that begins and ends within so short a time that it may be regarded mathematically as infinitesimal. The change produced in the medium, however, is generally of a finite amount. 2. A current surge of unidirectional polarity. See also pulse. impulse bandwidth -The area divided by the height of the voltage-response selectivity as a function of frequency. It is used in the calculation of broadband interference. impulse-driven clock- An electric clock in which the hands are moved forward at regular intervals by current impulses from a master clock. impulse excitation -Also called shock excitation. 1. A method of producing oscillatory current in which the duration of the impressed voltage is relatively short compared with that of the current produced. 2. The sudden application of a momentary steep-wavefront voltage to a resonant circuit, resulting in a damped oscillation.

impulse f r e q u e n c y

- incandescence

impulse f r e q u e n c y -The number of pulse periods per second generated by the dial-pulse springs in a telephone as they rapidly open and close in response to the dialing of a digit. impulse generator -Also called surge generator. 1. An electric apparatus that produces high-voltage surges for testing insulators and for other purposes. 2. A device that generates a broad energy spectrum by means of a very narrow impulse. Usually generated by discharging a short coaxial or waveguide transmission line. The pulses are discrete and regularly spaced, and are generally variable at a repetition rate from a few pulses per second to a few thousand pulses per second. The output of an impulse generator is specified as the rms equivalent of the peak voltage in dB above 1 microvolt per megahertz. 3. An oscillator circuit that generates electric impulses for synchronizing purposes in a television system. 4. A circuit, typically using a step-recovery diode, used to convert a sinusoidal input to a voltage impulse output. The basic circuit block in both step recovery diode multiples and comb generators. impulse noise-1. Noise due to disturbances having abrupt changes and of short duration. These noise impulses may or may not have systematic phase relationships. The noise is characterized by nonoverlapping transient disturbance. The same source may produce impulse noise in one system and random noise in a different system. 2. A type of communication-line interference characterized by high amplitude and short duration. 3. An unwanted signal characterized by a steep wavefront. impulse-noise generator- Equipment for generating repetitive pulses that provide random noise signals uniformly spread over a wide band of frequencies. impulse pay-per-view -Abbreviated IPPV. A feature of a decoder that allows an authorized subscriber to purchase a one-time scrambled program at will. IPPV shows are selected by a button on the decoder or its remote control. impulse period -See pulse period. impulse ratio -The ratio of the flashover, sparkover, or breakdown voltage of an impulse to the crest value of the power-frequency flashover, sparkover, or breakdown voltage. impulse relay- 1. A relay that stores enough energy from a brief impulse to complete its operation after the impulse ends. 2. A relay that can distinguish between different types of impulses, operating on long or strong impulses and not operating on short or weak ones. 3. An integrating relay. impulse response of a room-The time sequence of signals received at some point in a room due to a sound pulse generated at some other point in the room. It defines the arrival of a sound that has transversed the direct path between source and microphone and the arrivals of the various reflections. impulse sealing -A heat-sealing technique in which a pulse of intense thermal energy is applied to the sealing area for a very short time, followed immediately by cooling. It is usually accomplished by using an rf heated metal bar that is cored for water cooling, or is of such a mass that it will cool rapidly at ambient temperatures. impulse separator -Normally called sync separator. In a television receiver, the circuit that separates the synchronizing impulses from the video information in the received signal. impulse s p a r k o v e r voltage-The highest value of spark-gap or gas-discharge tube terminal voltage prior to ionization and the flow of discharge current.

366

impulse speed-The rate at which a telephone dial mechanism makes and breaks the circuit to transmit pulses. impulse strength-A measure of the ability of insulation to withstand voltage surges on the order of microseconds in duration. impulse timer -A timing device electrically powered by a synchronous motor, featuring a mechanical stepping device that enables it to advance a predetermined number of degrees within a predetermined time interval, controlling a multiple number of circuits. Said circuits are controlled by individual cams, which program their activity. impulse train -See pulse train. impulse transmission -The form of signaling used principally to reduce the effects of low-frequency interference. Impulses of either or both polarities are employed for transmission, to indicate the occurrence of transitions in the signals. impulse-transmitting relay-A relay in which a set of contacts closes briefly when the relay changes from the energized to the deenergized position, or vice versa. impulse-type telemeter-A telemeter that employs the characteristics of intermittent electric signals, other than their frequency, as the translating means. impurity-Also called dopant. 1. A material such as boron, phosphorus, or arsenic added to a semiconductor such as germanium or silicon to produce either p-type or n-type material. Impurities that provide free electrons are called donors and cause the semiconductor material to be n-type. Impurities that accept electrons are called acceptors and cause the material to be p-type. 2. A foreign material present in a semiconductor material, usually in small quantities. Some impurities are unwanted, and great pains are taken to extract them from the material. Others are intentionally added to semiconductor materials as dopants in order to modify their electrical behavior. 3. In semiconductor technology, a material such as boron, phosphoms, or arsenic added in small quantities to a crystal to produce an excess of electrons (donor impurity) or holes (acceptor impurity). impurity density-The amount of impurity material diffused into a certain volume of semiconductor material used in manufacturing semiconductor devices. impurity ions- An alien, electrically charged atomic system in a solid; an ion substituted for a constituent atom or ion in a crystal lattice, or located in an interstitial site in the crystal. impurity level-The energy level existing in a substance because of impurity atoms. inaccuracy- 1. The difference between the input quantity applied to a measuring instrument and the output quantity indicated by that instrument. The inaccuracy of an instrument is equal to the sum of its instrument error and its uncertainty. 2. The term sometimes used to indicate the deviation from an indicated or recorded value or the measure of conformity to an accepted standard. inactive leg -Within a transducer, an electrical element that does not change its electrical characteristics with the applied stimulus. Applied specifically to elements that complete a Wheatstone bridge in certain transducers. in-band signaling - 1. The transmission of signaling tones at some frequency or frequencies within the channel normally used for voice transmission. 2. A signaling scheme that uses the same path for both data and signaling information. in-band spurious transmitter output -A spurious transmitter output that lies within the specified band of transmission. incandescence -1. The state of a body with such a high temperature that it gives off light. 2. The generation

367 of light caused by passing an electric current through a wire filament. The resistance of the filament to the current causes the filament to heat up and emit radiant energy, some of which is in the visible range. incandescent lamp-1. An electric lamp in which electric current flowing through a filament of resistance material heats the filament until it glows. 2. A lamp that emits light when an electric current passes through a resistant metallic wire situated in a vacuum tube. 3. An electric lighting and signaling device operating on the principle of heating a fine metal wire filament to a white heat by passing an electric current through it. The filament wire has a positive temperature coefficient, which results in high inrush currents, up to 10 times the steady-state cunrent. INCH --Acronym for integrated chopper. It is a device designed to operate as a chopper, commutator, modulator, demodulator, or mixer, depending on circuit requirements. inching -See jogging. incidence angle-The angle between an approaching light ray or emission and the perpendicular (normal) to the surhce in the path of the ray. incidental FM-Also called residual FM. 1. The short-term jitter or undesired FM deviation of a local oscillator. It limits resolution when it approaches the IF bandwidth in magnitude. 2. Peak-to-peak variations of a carriler frequency caused by external variations not 2: part of' normal action of the carrier-tuned circuits. 3. In a klystron, frequency modulation of the fundamental frequency due to shot and ion noises, ac heater voltage, e:tc. incident field intensity-The field strength of a clown-conling sky wave, not including the effects of earth reflections at the receiving location. incident light-The light that falls directly on an otoject. incident-lightmeter- An exposure meter designed ID measure the light striking an object and used at a suitable location in the scene. Incident power-The product of the outgoing current and voltage traveling from a transmitter down a transmission line to an antenna. incident ray--A ray of light that falls on or strikes a surface of an object, such as a lens. It is said to be incident to the surface. incident wave -In a medium of certain propagation characteristics, a wave that strikes a gap in the medium or strikes a medium having different propagation characteristics. incipientfailure --A degradation failure in its beginning stages. in-circuit emulation-Abbreviated ICE. A capability provided on some microcomputer development systems that enables a system designer to use the facilities of the development system to debug prototype hardware and software. This is accomplished via an umbilical cable firom the development system that plugs into the microprocessor socket in the prototype system. See also emulation. in-circuit emulator- Abbreviated ICE. A microcomputer 'development system that can be plugged into a nricrocom~putersystem to control, alter, interrogate, and debug that system using a known good environment. irn-circuit tester -Also called a bed-of-nails tester or an in-situ tester. A tester that checks the individual components on a board using a fixture that provides access to each node of each component. Used to test for short and open circuits on bare boards, correct values of analog components (using a guarding technique), and correct functions iof individual ICs (using a pulsing technique).

incandescent lamp

- increment

inclination -1. The angle between the orbital plane of a satellite and the equatorial plane of the earth. 2. The angle that a line, surface, or vector makes with the horizontal. inclinometer- An instrument for measuring the magnetic inclination of the earth's magnetic field. it uses a magnetic needle that pivots vertically to indicate the inclination. inclusive AND-A logic element whose output is true if all inputs are true, all inputs are false, or all inputs but one are false. inclusive NAND-A logic element whose output is true if one and only one of the inputs is false. incoherent-Denotes the lack of a fixed phase relationship between two waves. If two incoherent waves are superposed, interference effects cannot last longer than the individual coherent times of the waves. incoherent detection-Detection wherein the information contained in the phase of the carrier is discarded. incoherent emitter -A fiber-optic source of radiation that has been used for short-length optical transmission lines. Light-emitting diodes are incoherent emitters. See coherent emitter. incoherent scattering-The disordered change in their direction of propagation that occurs when radio waves encounter matter. incoherent source -A fiber-optic light source that emits wide, diffuse beams of light of many wavelengths. The light waves emitted from an incoherent source are out of phase. Contrast coherent source. incoming -Describing a telecommunication trunk that is used only for calls coming in from another office. incoming selector-In a telephone central office, a selector associated with trunk circuits from another central office. incomplete sequencer relay -A device that returns the equipment to the normal, or off, position and locks it out if the normal starting, operating, or stopping sequence is not properly completed within a predetermined time. increductor-A controllable inductor similar to a saturable reactor, except that it is capable of operafing at high frequency (e.g., up to 400 MHz).

1

WINDING

8

ZONC

a 7

Zncreductor.

increment-1. A small change, either positive or negative, in the value of a variable quantity. 2. See step angle.

incremental compiler

- indicatingdemand meter

incremental compiler -In a computer, a compiler capable of compiling additional statements without a complete recompilation. incremental computer- 1. A computer in which the use of incremental representation of data is predominant. 2. A special-purpose computer designed specifically to process changes in the variables as well as absolute values of the variables. incrementaldigital-positiontransducer equalizer -Digital-position transducer that, without absolute position reference, produces a digital signal by motion. incremental digital recorder-A magnetic tape recorder that advances the tape across the recording head step by step, as in a punched-tape recorder. It is used for economical and reliable recording of an irregular flow of data. incremental frequency shift-A method by which incremental intelligence may be superimposed on other intelligence by shifting the center frequency of an oscillator a predetermined amount. incremental hysteresis loss -Losses in a magnetic material that has been subjected to a pulsating magnetizing force. incremental induction -One-half the algebraic difference between the maximum and minimum magnetic induction at a point in a material that has been subjected simultaneously to a polarizing and a varying magnetizing force. incremental integrator- A digital integrator modified so that the output signal is maximum negative, zero, or maximum positive when the value of the output is negative, zero, or positive, respectively. incremental permeability- 1. The ratio of the cyclic change in magnetic induction to the corresponding cyclic change in magnetizing force when the mean induction differs from zero. For small changes in magnetizing force, the incremental permeability is approximately equal to the slope of the minor hysteresis loop generated. 2. The ratio of incremental change in flux density to the incremental change in magnetizing force at any point on the hysteresis loop. incrementalsensitivity -The smallest change that can be detected by a particular instrument in a quantity under observation. incrementaltape -Magnetic tape written one character at a time instead of the usual method of continuous recording. incremental tuner -A television tuner in which antenna, rf amplifier, and rf oscillator inductors are continuous or in small sections connected in series. Rotary switches, connected to taps on the inductors, provide the portion of total inductance required for a channel, or shortcircuit all remaining inductance except that required for the channel. independent failure-A failure that has no significant relationship to other failures in a given device and can occur without interaction with other component parts in the equipment. independent load contacts -Contacts that can control electrical loads that must be isolated from the timer clutch solenoids and motor circuit. independent variable-One of several voltages and currents chosen arbitrarily and considered to vary independently. indeterminacy-The time coincidence uncertainty between an external input trigger pulse and an independently clock-derived output pulse from a timing unit such as a digital delay generator. It stems from a clock pulse versus trigger pulse phase uncertainty and is usually expressed in terms of nanoseconds or microseconds. For

368 example, the &1/2 clock pulse uncertainty of a 10-MHz source would be f 5 0 ns. indeterminatestate -The unknown logic state (X) of a memory element caused by critical races or oscillations, or existing after power is applied and before initialization. Some simulators can model indeterminate states and typically assign an X to indicate an indeterminate state. index counter -An odometer-type cumulative-digit indicator for keeping track of the amount of tape that has passed through a tape machine. The counter is generally driven by the takeup-reel turntable and thus registers rotation rather than tape footage, although the accuracy is generally good enough to allow for locating specific recorded segments according to previously noted index counter numbers. indexedaddress- An address that is altered by the content of an index register before or during the execution of a computer instruction. indexed addressing - 1. An addressing mode in which a computer finds the address of the desired memory location by referring to an index register. By successively adding or subtracting 1 to this index register, the computer can be made to step through a list or table. 2. An addressing system in which the address of the data is expressed as relative to the address stored in an index or pointer register. To obtain the absolute address, the offset address is added to the pointer address. This system is useful in processing tables or matrices of data. index hole-A hole punched in a floppy disk to indicate the beginning of the first sector. indexing-In a computer, a technique of address modification that is often implemented by means of index registers. indexing mechanism-A mechanical device on a rotary switch to Iocate and to maintain each position of the rotor. indexing slots -See polarizing slots. index matching fluid-In fiber optics, a fluid with a refractive index the same as a fiber core; used to fill the air gap between the fiber ends at connectors. index matching materials-Materials used in intimate contact between the ends of optical conductors to reduce coupling losses by reducing Fresnel loss. index of cooperation-In rectilinear scanning or recording, the product of the total length of a line and the number of lines per unit length. index of modulation -The modulation factor. index of refraction-1. Ratio of the speeds of light or other radiation in two different materials. This determines the amount the ray will be refracted or bent when passing from one material to the other, such as from air to water. The index of refraction of air is generally taken as unity. 2. The physical property of a material that describes the behavior of optical energy passing through it. It is defined as the ratio of the velocity of light in a vacuum to the velocity of light in the material. It varies with wavelength. index register-1. In a computer, a register that holds a quantity that may be used for modifying addresses or for other purposes, as directed by the program. 2. In a computer, a register whose contents can be added automatically to an address field contained in an instruction, when the indexing mode is specified. 3. A user-accessible register implicitly used for address computation by many instructions that reference main memory. indicating demand meter -A meter equipped with a scale over which a pointer is advanced to indicate maximum demand.

indicatingfuse - induced environment

369 indicating fuse-A protective device placed in a telephone circuit to provide visual and audible indication of a fault in the line. It consists of a fuse, pilot lamp, relay, and buzzer. When a line fault blows the fuse, the lamp lights and the buzzer sounds. indicating instrument -An instrument that visually indicates only the present value of the quantity being measured. indicatinglamp- A lamp that indicates the position of a device or the condition of a circuit. indicating meter-A meter that gives a visual indication of only the present or short-time average value of the measured quantity.

POiNlER

ADJUSTING SCREW

SCALE

indicating meter.

indication-The display to the human senses of information concerning a quantity being measured. indicator- An instrument that makes information available but does not store it. indicator gate -A rectangular voltage waveform applied to the grid or cathode circuit of an indicator cathode-ray tube to sensitize or desensitize the tube during the desired portion of the operating cycle. indicator tube -An electron-beam tube that conveys useful information by the variation in cross section of the beam at a luminescent target. indirect-acting recording instrument-An instrument in which the marking device is actuated by raising the level of measurement energy of the primary detector. This is done mechanically, electrically, electronically, photoelectrically, or by some other intermediate means. indirect address- An address in a computer instruction that indicates a location where the address of the referenced operand is to be found. indirect addressing - 1. A method of computer cross reference in which one memory location indicates where the correct address of the main fact can be found. 2. A method of storage addressing in which an addressed locatien contains an address rather than data. Quite often several levels of indirect addressing may occur before the sought-after data item is obtained. indirect light-Light from an object that has no selfluminous properties. Instead, it reflects light from another source. indirect lighting -A system of lighting in which all the light is directed to the ceiling or walls, which in turn reflect it to the objects to be illuminated. Lighting by luminaries distributing 90 to 100 percent of the emitted light upward. indirectly controlled variable-A variable that is related to and influenced by the directly controlled variable but is not directly measured for control. indirectly heated cathode --Also called equipotential or unipotential cathode. A cathode that is heated by an independent heater.

indirectly heated thermistor--A thermistor that incorporates, as part of its composite sfiructure, an electrical heater. A thermistor whose body temperature in use is significantly higher than the temperature of its surrounding medium as a result of current passing through its heater. indirect material-A type of semiconductor material in which electrons do not drop directly from the conduction band to the valence band, but drop in steps as a result of the trapping levels in the forbidden gap. indirect piezoelectricit’-The production of a mechanical strain in a crystal by applying a voltage to it (as opposed to the more common piezoe1ec’~ceffect of applying a strain to the crystal in order to produce a voltage). indirect radiative transition -See transition, 1. indirect scanning -A television technique used in early mechanical systems, and today in the flying-spot scanning of films. A small beam of light is moved across the subject and then reflected to a battery of phototubes. indirect synthesizer -A synthesizer employing phase-locked loops, digital dividers, and high-Q varactortuned oscillators. The discrete output frequencies are not limited to integer ratios of the reference frequency. Frequency step size or increments are primarily dedennined by the digital dividers. Switching speed between discrete output frequencies is usually limited by the phase-lock circuits. Applications include automatic test and satellite communications systems. indirect wave -A wave reaching a given reception point by a path from the transmitting point other than the direct-line path between the two (e.g., a sky wave received d e r deflection from the ionosphere layers). individualgap azimuth -In a magnetic-tape record or reproduce head stack, the angle of m individual gap relative to a line perpendicular to the precision-milled mounting pads in a plane parallel to the surface of the ta?e. individual line-A subscriber line that serves one main station and optional additional stations connected to the line as extensions; the line is not arranged for discriminatory ringing with respect to the stations. indoor antenna-Any receiving antenna located inside a building but outside the receiver. indoor transformer-A transformer that must be protected from the weather. Indox-The trade name of Indiana Steel Products Company’s barium ferrite permanent magnet alloy. induced -Produced by the influence of an electric or magnetic field. induced charge- 1. An electrostatic charge produced in one object by the electric field surrounding a nearby object. 2. An electrostatic charge produced on a conducting body when it is brought near to or connected to another body that bears an electric charge. induced current-1. The current that flows in a conductor that is moved perpendicularly to a magnetic field, or which is subjected to a magnetic field of varying intensity. The former takes place in an inductionmotor rotor; the latter, in the secondary winding of a transformer. 2. In induction heating, the current that flows in a conductor when a varying electromagnetic field is applied. 3. The current that results when a conductor is cut by magnetic flux lines. 4. Current that flows in a conductor because of an induced voltage. induced electromotiveforce -Represented by E ; proportional to the rate of change of magnetic flux through the circuit (dc$/dt). induced environment -The temperatures, vibrations, shocks, accelerations, pressures, and other conditions

induced failure - inductive circuit imposed on a system due to the operation or handling of the system. induced failure -A failure that is basically caused by a condition or phenomenon external to the item that fails. induced voltage-The voltage produced in a conductor when the conductor is moved up and down through the magnetic field of a second conductor, or when the field varies in intensity and cuts across the first conductor. Even though there is no mechanical coupling between the two conductors, the one producing the field will produce a voltage in the other. inductance-1. Property of a circuit that tends to oppose any change of current because of a magnetic field associated with the current itself. Whenever an electric current changes in value-rises or falls-in a circuit, its associated magnetic field changes, and when this links with the conductor itself, an electromotive force is induced that tends to oppose the original current change. Self-inductance is the full name for this, but the term inductance is usually used. The unit of inductance is the henry. When a current changing at the rate of 1 ampere per second induces a voltage of 1 volt, the inductance of the circuit is 1 henry. 2. See also coil. 3. The property of a circuit or circuit element that opposes a change in current flow, thus causing current changes to lag behind voltage changes. It is measured in henrys. inductance bridge-An instrument, similar to a Wheatstone bridge, for measuring an unknown inductance by comparing it with a known inductance. inductance coil-See inductor. inductance-tube modulation-A method of modulation employed in frequency-modulated transmitters. An oscillator control tube acts as a variable inductance in parallel with the tank circuit of the radiofrequency oscillator tube. As a result, the oscillator frequency varies in step with the audio-frequency voltage applied to the grid of the oscillator control tube. induction-1. The establishment of an electric charge or a magnetic field in a substance by the proximity of an electrified source, a magnet, or a magnetic field. 2. The setup of an electromotive force and current in a conductor by variation of the magnetic field affecting the conductor. induction brazing-The electric brazing process in which heat is produced by an induced current. induction coil-A device for changing direct current into high-voltage alternating current. Its primary coil contains relatively few turns of heavy wire; its secondary coil, wound over the primary, contains many turns of fine wire. Interruption of the direct current in the primary by a vibrating-contact arrangement induces a high voltage in the secondary. induction compass-A compass in which the indications are produced by the current generated in a coil revolving in the magnetic field of the earth. induction-conduction heater- A heating device through which electric current is conducted but is restricted by induction to a preferred path. induction density-See flux density. induction factor -In an alternating-current circuit, the ratio between that element of the current that does no work and the total strength of the current. inductionfield- 1. That portion of the electromagnetic field of a transmitting antenna that acts as if it were permanently associated with the antenna, and into which energy is alternately stored and removed. 2. The electromagnetic field of a coil carrying alternating current, responsible for the voltage induced by that coil in itself or in a nearby coil. 3. The magnetic field that is predominant

370 in the near zone of a radio transmitting antenna and that is directly proportional to the current in the antenna. induction frequency converter-A slip-ring induction machine driven by an external source of mechanical power. Its primary circuits are connected to a source of electric energy having a fixed frequency. The energy delivered by its secondary circuits is proportionate in frequency to the relative speed of the primary magnetic field and the secondary member. induction furnace-A furnace heated by electromagnetic induction. induction hardening -The process of hardening the surface of a casting by heating it above the transformation range by electrical induction, followed by rapid cooling. induction heating-The method of producing heat by subjecting a material to a variable electromagnetic field. Internal losses in the material then cause it to heat UP: induction instrument -An instrument operated by the reaction between the magnetic flux set up by one or more currents in fixed windings and the currents set up by electromagnetic induction in movable conductive parts. induction loudspeaker-A speaker in which the current that reacts with the steady magnetic field is induced in the moving member. induction motor- 1. An alternating-current motor in which the primary winding (usually the stator) is connected to the power source and induces a current into a polyphase secondary or squirrel-cage secondary winding (usually the rotor). Currents, and therefore magnetic poles, are induced into the secondary by the rotating primary magnetic field; thus, the armature rotates at slightly slower than synchronous speed, a condition that is called slip. The amount of slip increases with an increase in mechanical loading. 2. A motor that runs asynchronously; that is, not in step with the alternations of the alternating current. induction-motor meter-A meter containing a rotor that moves in reaction to a magnetic field and the currents induced into it. induction noise-The noise-other than thump, flutter, cross fire, or crosstalk-produced when two circuits are inductively coupled together. induction-resistancewelding -Welding in which electromagnetic induction alone causes the heating current to flow in the parts being welded. induction-ring heater-A core-type induction heater adapted principally for heating round objects. The core is open or can be taken off to facilitate linking the charge. induction soldering-A method of soldering in which the solder is reflowed or supplied by preforms. If the work is moved slowly through the energy field, the induction process may be made continuous. induction speaker-A speaker in which the current that reacts with the steady magnetic field is induced into the moving member. induction-voltage regulator-A device having a primary winding in shunt and a secondary winding in series with a circuit for gradually adjusting the voltage or the phase relation of the circuit by changing the relative positions of the exciting and series windings of the regulator. inductive-Pertaining to inductance or to the inducing of a voltage through mutual or electrostatic induction. inductive circuit-A circuit with more inductive than capacitive reactance. A circuit having a net inductive reactance; that is, a higher value of inductance reactance than of capacitive reactance.

37 1 inductive coordination-Location, design, construction, operation, and maintenance of electric supply and communication systems in a manner that prevents inductive interference. inductive coupled circuit-A network with two meshes having only mutual inductance in common. inductive coupling - 1. The association of one circuit with another through inductance common to both. When used without modifying words, the term commonly re.fers to coupling by means of mutual inductance, whereas coupling by means of self-inductance common to both circuits is called direct inductive coupling. 2. In inductive-coordination practice, the interrelation of neighboring electric supply and communication circuits resulting from electric and/or magnetic induction. 3. Coupling that exists between two circuits through a mutual inductance, such as that in a transformer. 4. Coupling between two circuits through an inductance that is common to the two circuits; direct inductive coupling. inductive feedback-The transfer of energy from .the output circuit to the input circuit of an amplifying (devicethrough an inductor or inductive coupling. inductive interference-1. Interference produced -in communication systems by induced voltages within ithe system. 2. Effect arising from the characteristics and inductive relations of electric supply and communication isystems of such character and magnitude as would ]preventthe communication circuit from rendering service satisfactorily and economically if methods of inductive (coordinationwere not applied. inductive kick- 1. The voltage, many times higher than the impressed voltage, produced by the collapsing ]field in a coil when the current through it is abruptly cut off. 2. A voltage surge that is induced in an inductance .when the current through it is interrupted and the magnetic lRux collapses suddenly. inductive level detector-A level-measuring system incorporating an oscillator and electromagnetic field. inductive load-Also called lagging load. A load that is predominantly inductive, so that the alternating lload cwent lags behind the alternating voltage of the 1,oad. An electrical load that has a significant inductive reactance. inductive microphone -See inductor microphone. inductive neutralization-Also called shunt or coil neutralization. A method of neutralizing an amplifier, whereby ithe equal and opposite susceptance of an inductor cancds the feedback susceptance caused by intereleinent capacitance. inductive pickup- Signals generated in a circuit or conductor due to mutual inductance between it and a disturbing source. inductive post-A metal post or screw extended across a waveguide parallel to the E field to act as inductive susceptance in parallel with the waveguide for purposes of tuning or matching. inductive reactance -The opposition to the flow of alternating or pulsating current by the inductance of a circuit. It is measured in ohms, and its symbol is X , . It is equal to 2n times the frequency in hertz times the inductance in henrys. inductive system -An ignition system that stores its primary energy in an inductor or coil. inductive transducer- A transducer in which changes i:n inductance convey the stimulus information. inductive transduction-The conversion of the measurantd into a change in the Self-inductanceof a single coil. inductive tuning-A method of tuning a radio by moving a core into and out of a coil to vary the inductance.

inductive coordination

- industrial television

inductive winding --A coil through which a varying current is sent to give it an inductance. inductive window -A conducting diaphragm extended into a waveguide from one or both sidewalls t~ act as an inductive susceptance in parallel with the waveguide. inductometer-An inductor whose inductance can be varied, sometimes by a calibrated amount. inductor -Also called inductance or retardation coil. 1. A conductor used for introducing inductance into an electric circuit. The conductor is wound into a spiral, or coil, to increase its inductive intensity. 2. A passive fluidic element that, because of fluid inertness, has a pressure drop that leads flow by essentially 90". 3. See coil.

TOROID

SOLENOlO

Inductors.

inductor microphone- Also called indnctive microphone. A microphone in which the sound waves move a conductor back and forth, cutting magnetic lines of force and producing an electrical output of the same frequency and proportional to the amplitude of the sound waves. inductor-type synchronous motor -A type of synchronous motor having field magnets that are fixed in magnetic position relative to the armature conductors, the torques being produced by forces between the stationary poles and salient rotor teeth. Such motors usually have permanent-magnet field excitation, are built in fractionalhorsepower frames, and operate at low speeds (300 revolutions per minute or less). lnductosyn-An extremely precise transducer based on the magnetic circuit of a conductor deposited on glass for stability, and operated at a relatively high frequency. Extremely accurate, but requires much auxiliary equipment (Farrand Controls Inc.). industrial-grade IC -Typically, an integrated circuit whose performance is guaranteed over the temperature range 0 to 70°C. industrial radio services -Radiocommunication services essential to, operated by, and for the sole use of those enterprises that require radiocommunications in order to function efficiently. industrial television -The cameras and related instrumentation of a closed-circuit television system. Such equipment is designed to function in the different environments found in industrial processes. Used to monitor areas that are hazardous to personnel, such as high-radiation

industrial timer

- information center

areas, areas that do not require steady supervision, industrial processes for surveillance or quality control, or areas requiring security measures. industrial timer-A timing device, impulse or constant-speed type, used in industrial applications other than the appliance industry. industrial tube -A vacuum tube designed for industrial electronic equipment. inelastic collision -Collision resulting in excitation of a molecule. inertance -Acoustical equivalent of inductance. inert gas-See noble gas. inertia-1. The tendency of an object at rest to remain at rest, or of a moving object to continue moving in the same direction and at the same speed, unless disturbed by an outside force. Resulting from mass and inhibiting change in velocity. Important in pickup mechanics. 2. The resistance to change in speed or velocity. In stepper motors, inertia does not affect the maximum stepping rate, only the time required to attain it. inertial guidancehavigation -A self-contained system for navigation in which position can be computed by knowing a craft’s starting point and where it has been. Changes in acceleration are detected by gyroscopes for direction and attitude and by accelerometers for velocity. These signals are integrated to determine resulting velocity and distance. The system needs no outside reference and cannot be jammed. inertial navigation- 1. A guidance technique in which airframe acceleration is first measured and then integrated twice with respect to time in order to determine the distance traveled. External aids such as radio and radar are not necessary. The acceleration or deceleration of the airframe is measured continuously with accelerometers oriented in some convenient frame of reference, usually corresponding to the earth’s north-south, east-west coordinates. 2. A form of navigation that uses dynamic measurements of acceleration forces acting on a gyroscopically stabilized device as a basis for computing position and velocity information. This device, which is mechanized so as to be completely self-contained, has the inherent capability of providing continuously available navigation information in terms of conventional, directly usable latitude and longitude coordinates. inertia relay-A relay having added weights or other modifications that increase its moment of inertia and either slow it or cause it to continue in motion after the energizing force is removed. inertia s w i t c h -A switch capable of sensing acceleration, shock, or vibration. It is designed to actuate upon an abrupt change in velocity. inertia welding -A forge-welding process in which stored kinetic energy is released as frictional heat when two parts are rubbed together under the proper conditions. infant mortality -The occurrence of premature catastrophic-type failures of a component or equipment

INFANT MORTALIT?

Znfant mortality.

372 at a rate substantially greater than that observed during life prior to wearout. infant-mortality period -See early-failure period. inferential -The kind of instrumentation, especially its signal source, in which there is sampling of an entirely different quantity from the one of interest, upon the assumption that they vary in perfect proportion. Linearity or a perfectly repeatable relationship between the two is inferred for the sake of a more convenient signal-source arrangement. infiltration-The process of filling the pores of a sintered compact with a metal or alloy of lower melting point. infinite -Boundless; having no limits whatsoever. infinite baffle- 1. An airtight speaker enclosure that completely absorbs or dissipates a speaker’s rear sound waves. 2. A speaker mounting in which ideally there is no path of air between the back and front of the speaker diaphragm. An infinite baffle improves the forward radiation of sound at low frequencies and preferably should be a very large plane surface, like the wall of a room or a screen of very rigid material (e.g., 3/4-inch or 2-cm wood), on which a speaker is mounted. (In practice, truly infinite bafiles are rarely accomplished except in sealed boxes, but these give rise to problems of resonance.) 3. An airtight speaker enclosure containing a bass speaker with very low open-air resonance, plus a sealed midrange speaker and tweeter. infinite-baffle s p e a k e r system-A speaker in which the bass driver is located in an almost airtight enclosure. infinite-impedance detector-A detector circuit in which the load is a resistor connected in parallel with an rf bypass capacitor between the cathode and ground. Since the grid is always negative with respect to the cathode, the tube presents an infinite impedance to the input. infinite line-A transmission line with the same characteristics as an ordinary line that is infinitely long. infinite resolution-The capability of a device to provide continuous output over its entire range. infinitesimal -Jmmeasurably small; approaching zero. infinity- 1. A hypothetical amount larger than any assignable amount. 2. A number larger than any number a computer can store in any register. 3. Any distance of a subject from a lens for which the image no longer moves when the subject moves along the optical axis. infinity device-Also called harmonica bug. A surreptitious listening device that uses the telephone as a sensor. Allows the bugger to listen to sounds near the phone while the phone is not in use. Does not allow him or her to hear telephone conversations. inflection point-The point at which a curve changes direction. infobond -An automated system of point-to-point wiring on the back of a two-sided printed wiring board (the components are on the front, or other side). The No. 38 AWG copper wire used is solder-bonded to terminations by an automatic soldering gun. information -1. In computing, the basic data and/or program entered into the system. 2. That property of a signal or message whereby it conveys something meaningful and unpredictable to the recipient, usually measured in bits. 3. Data that has been organized into a meaningful sequence. information bits -In telecommunications, those bits originated by the data source and not used for error control by the data-transmission system. information center-A facility specifically designed for storing, processing, and retrieving information

373 to be disseminated at regular intervals, on demand, or selectively, according to the needs of users. information channel -The transmission and intervening equipment involved in the transfer of information in a given direction between two terminals. An information channel includes the modulator and demodulator and any error-control equipment irrespective of its location, as well as the backward channel, when provided. information extraction-An analysis of an image to recognize and isolate a specific feature or relationship among fieatures. informationfeedback system -In telecommunications, a i information-transmission system in which an echo check is employed to verify the accuracy of the transmission. information gate-A circuit that permits information or data pulses to pass when the circuit is triggered by an external source. informationhandling -The storing and processing of information and its transmission from the source to the user. Information handling excludes the creation and use of information. information processing -A term that encompasses both word processing and data processing. It describes the entire scope of operations performed by a computer. information rate-In computers, the minimum number of binary digits per second required to specify the source messages. information rate changer-A device that speeds up ttae playback of tape-recorded speech without pitch change or detePioration of characteristic resonances. This is acconiplished by rotating the playback head in the direction of tape travel. information retrieval- 1. A method for cataloging vast amounts of data related to one field of interest so that any part or all of this data can be called out at any time with accuracy and speed. 2. The recovery of data that has been stored at a particular address in a memory. 3. A technique of classifying and indexing useful data in mass storage devices in a format amenable to interaction with the user@). 4. The art of storing information so that it may be recovered easily. Branches include abstracting, locating facts of interest, and language translation. information-retrieval system - A system for locating and selecting on demand certain documents or other graphic records relevant to a given information requirement from a file of such material. information separator-A control character used to identify a logical boundary of information. The name of the separator is not necessarily indicative of what it separates. information superhighway-The concept of a high-bandwidth network that links everyone with everyone and can transport all media types. The information superhighway links the concepts of online services, Internet, and interactive TV together. information system -A group of computer-based systems and data required to support the information needs of one or more business processes. informationtheory- 1. The branch of learning that deals with the likelihood of accurate transmission of messages subject to transmission failure, distortion, and noise. 2. The mathematical theory that deals with the transmission of information and the effects of bandwidth, distortion, and noise. infra- -Prefix meaning below; beneath; less than. infradyne receiver-A superheterodyne receiver whose intermediate frequency is made higher than the signal frecluency in order to obtain high selectivity.

information channel - infrared guidance infrared-Abbreviated IR. 1. Pertaining to or designating those radiations with wavelengths just beyond the red end of the visible spectrum, such as those emitted by a hot body. These wavelengths are longer than those of visible light and shorter than those of radio waves. 2. That section of the electromagnetic spectrum, invisible to the eye, lying between wavelengths of 750 nm and about 1 mm. Thermography utilizes waves in this region for recording changes in temperature. 3, Part of the electromagnetic spectrum between the visible light range and the radar range. 4. The electromagnetic wavelength region between approximately 0.75 and 1000 micrometers. For fiber-optic transmission, the near-infrared region between 0.75 and 1.3 micrometers is the most relevant region because glass, light sources, and detector techniques are most nearly matched in this wavelength region. infrared alarm systems-A system that uses infrared detectors and related instrumentation to determine when abnormal amounts of infrared radiation, usually in the form of heat, are present in an area; used for the detection of fires or the presence of intruders in a restricted area. infrared binoculars-An instrument, similar in design to regular binoculars, that can transmit and enlarge infrared images using electronic circuits. infrared communications set-The collection of components necessary to operate a two-way electronic system in which infrared radiation is used to c q intelligence. infrared counter-countermeasures-Action taken to employ infrared radiation equipment and systems in spite of enemy measures to counter their use. infrared countermeasures -Action taken to reduce the effectiveness of enemy equipment employing infrared radiation. infrared detector-A transducer that is sensitive to invisible infrared radiation (wavelengths between 0.75 and 1000 micrometers), usually using a semiconductor (photon), thermocouple bolometer, or pneumatic (pressure) device to detect the radiation. Also a device used to detect radiation from the infrared region. infrared emitter-See infrared light-emitting diode. infrared-emitting diode- 1. A semiconductor device with a semiconductor junction in which infrared radiant flux is nonthermally produced when a current flows as a result of applied voltage. 2. A pn diode in which a fraction of the injected minority carriers recombine by means of radiative transistors. When the junction is forward biased, electrons from the n region are injected into the p region, where they recombine with excess holes. In the radiative process, energy given up in recombination i s in the form of photon emission. The generated photons travel through the lattice until they are either reabsorbed by the crystal or escape from the surface as radiant flux. infrared guidance - A system using infrared heat resources for reconnaissance of targets or for navigation.

TO CONTROL SYSTEM

INFRARED --

LOW-LEVEL ELECTRICAL SIGNAL

Infrared guidance.

infrared homing

- initial contact chatter

infrared homing-A type of missile homing in which the guidance system tracks the target from the infrared radiation it emits. See heatseeker. infrared instruments- Any of the photoelectric and thermal detectors, spectrographs and monochromators, thermographs, scanners, amplifier tubes, snooperscopes, and related equipment especially developed for use with infrared radiation. infrared jamming -A countermeasure used against heatseeking missiles to reduce their effectiveness. Normally it involves the emittance of infrared radiation at a level that will overload the missiles' detectors. infrared light-Light rays just below the red end of the visible spectrum. infrared light-emitting diode- Also called infrared emitter. An optoelectronic device containing a semiconductor pn junction that emits radiant energy in the 0.75- to 100-micrometer wavelength region when forward biased. infrared motion detector -A sensor that detects changes in the infrared light radiation from parts of the protected area. Presence of an intruder in the area changes the infrared light intensity from his or her direction. infrared optics -Lenses, prisms, and other optical elements for use with infrared radiation (radiation with a wavelength between 0.75 and 1000 micrometers). infrared ovens-Units that dry, cure, and preheat parts directly (Le., without heating the oven air) via infrared energy. infrared radiation -1. Invisible radiation with wavelengths in the range between 7500 angstroms (red) and about 1,000,000 angstroms (microwaves). 2. The electromagnetic wavelength region between approximately 0.75 and 1000 micrometers, longer than the wavelength of visible light. infrared radiation sources- Almost any warm thing, from an electric blanket to a living human being, that acts as a source for the longer wavelength end of the IR range, which generally is regarded as extending from 0.75 to 1000 micrometers. Calibrated secondary sources are usually a heated cavity (blackbody) or a carbon filament lamp rated in wattage output or in ergs per second of radiation incident on a surface at a specified distance. infrared sources-Emitters of radiation with a wavelength between 0.75 and 1000 micrometers. infrared spectrum-That portion of the electromagnetic spectrum between the wavelengths of 0.75 and 1000 micrometers. infrared thermometer-A temperature-measuring device that detects infrared radiation from an object and converts that measurement into a reading representing the temperature of the object. infrared waves -Also called black light. Invisible waves longer than the longest visible red light waves but shorter than radio-frequency waves. infrared window -A region of relatively high transmission in the infrared-frequency range. infrasonic -Pertaining to frequencies below the range of human hearing, hence below about 15 hertz. Formerly called subsonic. infrasonic frequency-A frequency below the audio range. Infrasonic vibrations can be felt but not heard. Replaces the obsolete term subsonic frequency. inharmonic frequency-A frequency that is not a rational multiple of another frequency. inherent delay-Delay between the insertion of information into a unit and presentation of the information at the output. For example, a delay inserted into the CRT vertical amplifier of pulse analyzers to allow the leading

374 BLUE GREEN YELLOW ORANGE REO

IO&

Infrared spectrum. edge of the signal triggering the sweep to be seen. See also insertion delay. inherent interference-A type of electromagnetic interference generated within a receiver by thermal agitation, shot effect, and nonlinear impedance. inherent reliability-The potential reliability of an item present in its design. inherited error-In a computer, the error in the initial values, especially that error accumulated from prior steps in a step-by-step integration. inhibit-To prevent an action from taking place or data from being accepted by applying an appropriate signal (generally a logic 0 in positive logic) to the proper input. inhibit gate-A circuit that provides an output only when certain signals are present and other signals are not present at the inputs. inhibiting input-A computer gate input which, if in its prescribed state, prevents any output which might otherwise occur. inhibiting signal -A signal whose presence prevents an operation from taking place. inhibition gate-A gate circuit used as a switch and placed in parallel with the circuit it is controlling. inhibitor-Also called inhibition gate. In a digital computer, a logic circuit that clamps a specified output to the zero level when energized. inhibit pulse-A computer drive pulse that tends to prevent certain drive pulses from reversing the flux of a magnetic cell. initial actuation time-The time of the first closing of a previously open contact of a relay or the first opening of a previously closed contact. initial contact chatter-That chatter caused by vibration produced by opening or closing the contacts in a relay themselves, as by contact impact in closure.

375

initial differential capacitance -The differential capacitance of a nonlinear capacitor when the capacitor voltage is zero. initial drain-The current supplied at nominal voltage by a. cell or battery. initial element-See primary detector. initial erection -The mode of operation of a vertical gyro in which the gyro is being erected or slaved initially. The initial erection rate is usually relatively fast. initial failure-The first failure that occurs in use. initial inverse voltage-Of a rectifier tube, the peak inverse anode voltage immediately following the conducting period. initial ionizing event -Also called primary ionizing event. An ionizing event that initiates a tube count. initialization-1. The process in which information (memory locations for data and results, tolerances, limits, etc.) is supplied to a computer prior to the running of a program. 2. Applying input patterns to a logic circuit so that all internal memory elements achieve a known logic state. 3. A process that takes place whenever the state of a device or program must be known at startup. initialize- 1. To set counters, switches, and addresses to their starting values at the beginning of a computer routine or at prescribed points in the routine. 2. To establish an initial condition or starting state; for example, to set logic elements in a digital circuit or the contents of a storage location to a lmown state so that subsequent application of digital test patterns will drive the logic elements to another known state. 3. To reset a computer and its peripherals to a starting state before beginning a task. Done automatically by the disk operating system. initializing--1. The preliminary steps in arranging those instructions and data in a computer memory that are not to be repeated. 2. Setting flip-flops to known states prior to testisg. initial permeability-The slope of the normal induction curve at zero magnetizing force. Permeability at a field density approaching zero. initial program loader -The procedure that results in loadirng of the initial part of an operating system or other program SO that the program can then proceed under its own Icwntrol. initial reversible capacitance -In a nonlinear capacitor, the reversible capacitance at a constant bias voltage of zero. initial-velocity current-A current that flows between an electrode, such as the grid of a vacuum tube, and its czhode as a result of electrons thrown off from the cathode because of heat alone. Their velocity is sufficient to allow the electrons to reach the grid unaided by an accekrating field. injected laser-See diode laser. injection grid --A vacuum-tube grid that controls the eleclson stream without causing interaction between the screien and control grids. In some superheterodyne receivers, the injection grid introduces the oscillator signal into the mixer stage. injection laser-Also known as a pn junction laser. 1. An optical oscillator or amplifier that has as its active medium a fonvard-biased semiconductor diode in which a population inversion has been established between the conduction and valence bands. Radiation is emitted in the process of recombination across the bandgap. High frequency imodulation of the output beam can be achieved by modulating the input current. Usually, the optical resonator is formed by cleaving or polishing opposite faces of the diode crystal. Typical dimensions of the device are 0.4 nun x 0.1 mm x 0.5 mm. 2. A semiconductor diode carrying a high current in the forward direction. Radia:ion is produced as electrons recombine with holes in the

initial differential capacitance

- ink blending

junction region. For coherent emission, the current density must exceed a threshold commonly about 10,000 Ncm2 for gallium arsenide diodes. 3. A solid-state semiconductor device with at least one pn junction capable of emitting coherent or stimulated radiation under specified conditions. Incorporates a resonant optical cavity. 4. A solid-state laser having at least one pn junction. Its energy level transitions are between energy bands of semiconductors and it can be tuned in frequency by temperature or pressure alterations and by the effect of a magnetic field. injection Baser diode- 1. A coherent radiant source LED consisting of an extremely flat junction area, end mirrors, and direct bandgap semiconductors, having a Fabry-Perot optical cavity. 2. Ln fiber optics, a semiconductor device in which lasing takes place within the pn junction. Light is emitted from the diode edge.

LASER FLUX

PDLI~HED (CLEAVED) SURFACE

\

‘P+ TYPE \,.TYPE N.TYPE

Injection laser diode.

injection-locked oscillator -Abbreviated E O . A free-running microwave oscillator that is stabilized by injecting a reference signal into the oscillator’s resonant circuitry. The required injected signal level is determined by the output signal characteristic requirements (Le., noise, stability, etc.) and is typically in the range of 70 to 30 dB below the output level of the ILQ. injection luminescent diode- 1. A gallium arsenide diode, operating in either the laser or noncoherent mode, that can be used as a source of visible or near infrared light for use in triggering such devices as lightactivated switches. 2. A semiconductor (gallium arsenide) diode operating in either a coherent or incoherent mode that is used as a near-infrared or visible source. in triggering light-activated devices. injector-An electrode on a spacistor. ink- 1. One of several conductive materials used for chip bonding, electrostatic shielding, corona shielding, making connections, repairing on printed circuits, attaching leads, adhesive work, ignition cable sheath coating, and making electrodes, contacts, terminations, and surfaces receptive to plating, etc. 2. Synonymous with composition and paste when relating to screenable thick-film materials, usually consisting of glass frit, metals, metal oxide, and solvents. 3. In hybrid technology, the conductive paste used on thick-film materials to form the printed conductor pattern. Usually contains metals, metal oxide, glass frit, and solvent. 4. In thick film, composition of micrometer-size polycrystalline solids suspended in a thixotropic vehicle. The solids are chosen for their electrical characteristics (i.e., metals for conductives, metals and oxides for resistives, and glasses for glazes and dielectrics). ink blending -See blending.

ink-jet printer - input impedance

376

ink-jet printer- A nonimpact printer that forms letters and numbers by electrostatically aiming a jet of ink onto the paper.

DROP GENERATOR

DRIVER

CHARGE ELECTRODE

SUPPLY CONTROL

FORMATION

RESERVOIR FOR RECYCLING

Ink-jet printer. ink-jet printing -A nonimpact printing technique that utilizes droplets of ink to form copy images. As the print head moves across the surface of the copy paper, it shoots a stream of tiny, electrostatically charged ink drops at the page, placing them precisely to form individual print characters. ink-mist recording -Also called ink-vapor recording. In facsimile, electromechanical recording in which particles of an ink mist are deposited directly onto the record sheet. ink recorder-The ink-filled pen or capillary tube that produces a graphic record. ink recording-A type of mechanical facsimile recording in which an inked helix marks the record sheet. ink-vapor recording -See ink-mist recording. inleads-Those portions of the electrodes of a device that pass through an envelope or housing. in-line heads-See stacked heads. in-line procedures- 1. In COBOL, the procedural instructions that are part of the main sequential and controlling flow of the program. 2. Short functions whose code is inserted by the compiler at the point of call, thereby avoiding the overhead of a normal function call. in-line processing -The processing of data in random sequence not subject to preliminary sorting or editing. in-line subroutine-A subroutine that is inserted directly into the linear operational sequence. Such a subroutine must be recopied at each point in a routine where it is needed. in-line tuning -The method of tuning the intermediate-frequency strip of a superheterodyne receiver in which all the intermediate-frequency amplifier stages are made resonant to the same frequency. inorganic electrolyte -A solution that conducts electricity due to the presence of ions of substances not of organic origin. in phase-Two waves of the same frequency that pass through their maximum and minimum values of like polarity at the same instant are said to be in phase. in-phase portion of t h e c h r o m i n a n c e signalThat portion of the chrominance signal having the same phase as, or exactly the opposite phase from, that of the

subcarrier modulated by the I signal. This portion of the chrominance signal may lead or lag the quadrature portion by 90 electrical degrees. input -1. The current, voltage, power or other driving force applied to a circuit or device. 2. The terminals or other places where current, voltage, power, or driving force may be applied to a circuit or device. 3. Data to be processed. 4. The process of transferring data from an external computer storage to an internal storage. 5. The terminals, jack, or receptacle provided for the introduction of an electrical signal or electric power into a device or system. input admittance-1. The reciprocal of the input impedance. 2. The admittance between the input terminals with the outputs shorted together. input area-In a computer, the area of internal storage into which data from external storage is transferred. input bias current-1. The current that must be supplied to each input of an IC operational amplifier to assnre proper biasing of the differential-input-stage transistors. In specification sheets, this term refers to the average of the two input bias currents. 2. One-half the sum of the separate currents entering the two input terminals of a balanced amplifier. 3. The average of the two input currents of an operational amplifier. input block-In a computer, a section of the internal storage reserved for receiving and processing input data. input capacitance- 1. The capacitance at the input terminals of a device. 2. The capacitance between gate and source terminals of a field-effect transistor at specified bias and frequency conditions, with the drain ac shortcircuited to the source. input channel-A channel through which a state is impressed on a device or logic element. input common-mode range-The maximum input that can be applied to either input of an operational amplifier without causing damage or abnormal operation. input common-mode rejection ratio -1. The ratio of the change in input voltage to the corresponding change in output voltage, divided by the open-loop voltage gain. 2. The ratio of the full differential voltage gain to the common-mode voltage gain. input common-mode voltage range-The range of voltages on the input terminals of an operational amplifier for which the amplifier is operational. Note that the specifications are not guaranteed over the full common-mode voltage range unless specifically stated. input device- 1. The device or set of devices through which data is brought into another device. 2. A device such as a card reader or terminal keyboard that converts data from the form in which it has been received into electronic signals that can be interpreted by the computer. input e q u i p m e n t -The equipment that introduces information into a computer. input error voltage-The error voltage appearing across the input terminals of an operational amplifier when a feedback loop is applied around the amplifier. input extender-A high-speed diode array used in a logic circuit when increased fan-in capability is required. input formatting -The technique a system uses to put all entered data into a standard (or intelligible) format. input gap -Also called buncher gap. In a microwave tube, the gap where the initial velocity modulation of the electron stream occurs. input impedance- 1. The impedance a transducer presents to a source. 2. The effective impedance seen looking into the input terminals of an amplifier; circuit details, signal level, and frequency must be specified. 3. The impedance that exists between the input terminals

377

input impedance of a transmission line - insertion force

of an amplifier or transmission line when the source is disconnected. input impedance of a transmission line-The impedance between the input terminals with the generator disconnected. input offset current-The difference between the input bias currents flowing into each input of an IC operational amplifier, when the output of the operational amplifier is at zero volts. lnput offset voltage-That voltage which must be applied .between the input terminals of an operational amplifier, through two equal resistances, to obtain zero output voltage. inputloutput -Abbreviated YO. 1. Pertaining to devices ithat accept data for transmission to a computer system ((input) or that accept data from a computer system for transmission to a user or process. Devices that perfoim both functions are known as I/O devices (e.g., terminals). 2. A general term for the peripheral devices used to communicate with a digital computer, and the data involved in the communication. 3. The process off transmitting information from an external source to an equipment unit, or from an equipment unit to an external source. 4. Transferring information from an input to an accumulator, or from an accumulator to an output. 5. Interface circuits or devices offering access between external circuits and the central processing unit or memory. ~ n p u t - ~ u bound ~ p u ~-See input-output limited. ~ n ~ u ~ ~ oconnector-A ut~ut mating pair of connectors used to cany signals into and out of a panelmounted subsystem. An example is a connector pair that interconnects the individual back panels in a large array of panels. ~nput-output limited -Also called input-output bound. F’ertaining to a system or condition in which the time taken by input and output operations exceeds the time for other operations. input pins-The terminals of the device to which input logic signals may be applied. input-power rating -Also called coil rating. A statement of the allowable voltage, current, or power to the actuating element of a relay beyond which unsatisfactory performances will occur. input process- 1. The process in which a device receives data. 2. The transmission of data from peripheral equipment or external storage to internal storage. input recorder-Any device that makes a record of an input electrical signal. current -In dc-dc converters, urrent generated by the switching transients. The value of this current should not exceed 1 of the nominal input current. t reflected ripple-A dc-dc converter term that describes the voltage spike resulting from switching generated transient currents as measured at the dc input source. input register-In a computer, the register of internal storage able to accept information from outside the computer at one speed and supply the information to the computer calculating unit at another, usually much greater, speed. input resistance -Also called differential input resistance. The small signal resistance measured between the inverting and noninverting inputs of an operational amplifier. Input capacitance is the capacitance seen between the same two inputs. input resonator-The buncher resonator in a velocity-modulated tube. It modifies the velocity of the electrons in the beam.

input sensitivity-The input signal level that will result in rated output of a piece of amplifying equipment. In preamplifiers, it is the signal that gives the rated voltage output of the preamplifier; in power amplifiers, the signal that gives the rated power output. (In preamplifiers, the phono sensitivity is commonly 1 millivolt; highlevel inputs, such as tape and tuner, are commonly 250 millivolts. In power amplifiers, common values are between 0.5 and 1.0 volt.) input transformer- A transformer that transfers energy from an alternating-voltage source to the input of a circuit or device. It usually provides the correct impedance match as well. input uncertainty-In an operational amplifier, the algebraic sum of all the factors, including environmental and time effects, that contribute to the nonideal behavior of the input circuit. input unit-In a computer, the unit that takes information from outside the computer into the computer. input voltage drift-The change in output voltage of an operational amplifier divided by the open-loop gain, the quotient expressed as a function of temperatwe or time. input voltage offset-The dc potential difference between the two inputs of a differential amplifier when the potential difference between the output terminals is zero. input winding -See signal winding. inquiry- 1. The withdrawal of stored information from an electronic data processing system by interrogating the contents of the storage of a computer. 2. A technique for initiating the interrogation of the contents of the storage of a computer. inquiry station -A remote terminal from which an inquiry may be sent over a wire line to a computer. inquiry unit-A device used to extract a quick reply to a random question regarding information in a computer storage. inrush-The initial surge of current through a load when power is first applied. Lamp loads, inductive motors, solenoids, contactors, valves, and capacitive load types all have inrush or surge currents higher than the normal running or steady-state currents. Resistive loads, such as heater elements, have no inrush. inrush current-1. The current in a load circuit immediately following twm-on. In capacitive and tungsten-lamp loads, this exceeds steady-state current for some period following turn-on. 2. In a solenoid or coil, the steady-state current drawn from the line with the armature in its maximum open position. inrush current limiting -Protective circuit in a power supply that prevents excessively large currents through a rectifier to charge the filter capacitors. TO prevent unnecessary power loss. the circuit is usually inhibited after the capacitors attain full charge. insert core -An iron core used generally for adjusting an inductor to a fixed frequency. It consists of a threaded metal insert molded or cemented into one or both ends of the core. insert earphones-Small earphones that fit partially inside the ear. insertion delay- Also called inherent delay, intrinsic delay, and propagation delay. The interval for a circuit or instrument to respond with an output after being triggered either internally or externally. It is usually implied that the numerically expressed period is an irreducible minimum. insertion force-1. Of a connector, the force needed to fully engage a connector plug and receptacle. Depending on the number, arrangement, and size of the contact pins, in addition to the strength of the springs,

insertion gain

- instruction length

their surface finish, and the rigidity of their mountings, the required mechanical insertion force will be dictated to a great extent by the life expectancy of the connectors, the intended use, the speed of insertion, and their immunity to shock and vibration. 2. The effort, usually measured in ounces, required to engage mating components. insertion gain-The gain resulting from the insertion of a transducer in a transmission system is the ratio of the power delivered to that part of the system following the transducer to the power delivered to that same part before insertion. (If more than one component is involved in the input or output, the particular component used must be specified. This ratio is usually expressed in decibels.) insertion loss- 1. The difference between the power received at the load before and after the insertion of apparatus at some point in the line. 2. The loss in load power resulting from the insertion of a component, connector, or device. Insertion loss is expressed in decibels as the ratio of power received at the load before insertion to the power received at the load after insertion. 3. Signal-power loss resulting from connecting communication equipment with dissimilar impedance values. 4. A power loss that results from inserting a component into a previously continuous path or creating a splice in it. insertion p h a s e shift-The change in phase of an electric structure when inserted into a transmission system. insertion s w i t c h -A process by which information is inserted into a computer by the manual operation of switches. insertion tool -A small, hand-held tool used to insert contacts into a connector. inside lead-See start lead. inside spider-A flexible device placed inside a voice coil to center it with the pole pieces of a speaker. in-situ tester -See in-circuit tester. inspection c h a m b e r - In a spectrophotometer, the part in which the solution to be tested is placed for analysis. inspectoscope-An instrument for viewing quartz crystals, while they are immersed in oil, to determine mechanical faults, the approximate direction of the optical axis, and regions of optical twinning. instability- 1. The measure of the fluctuations or irregularities in the performance of a device, system, or parameter. 2. An undesired change that occurs over a period of time and that is not related to input, operating conditions, or load. instantaneous automatic gain control -Abbreviated instantaneous AGC. A portion of a radar system that automatically adjusts the gain of an amplifier for each pulse so that there is a substantially constant outputpulse peak amplitude with different input-pulse peak amplitudes. The circuit is capable of acting during the time in which a pulse is passed though the amplifier. instantaneous companding -Companding that varies the effective gain in response to instantaneous values of the signal wave. instantaneous contacts-Contacts that are actuated immediately when a starting signal is applied to a timer. instantaneous disc -A blank recording disc that can be played back on a phonegraph immediately after being cut on a recorder. instantaneous frequency-The rate at which the angle of a wave changes when the wave is a function of time. If the angle is measured in radians, the frequency in hertz is the rate of change of the angle divided by 2n. instantaneous overcurrent relay- Also called rate-of-rise relay. A device that functions instantaneously on an excessive value of current or on an excessive rate

378 of current rise, thus indicating a fault in the apparatus of the circuit being protected. instantaneous power-The power at the points where an electric circuit enters a region. It is equal to the rate at which the circuit is transmitting electrical energy into the region. instantaneous power output-The rate at which energy is delivered to a load at a particular instant. instantaneous readout -Readout by a radio transmitter at the instant the information to be transmitted is computed. instantaneous recording -A recording intended for direct reproduction without further processing. instantaneous sampling -The process of obtaining a sequence of instantaneous values of a wave. These values are called instantaneous samples. instantaneous sound pressure -The total instantaneous pressure at a certain point, minus the static pressure at that point. The most common unit is the microbar. instantaneous s p e e c h power-The rate at which the speaker is radiating sound energy at any given instant. instantaneous speed variations-See ISV. instantaneous start-stop rate-The maximum stepping rate that can be attained by an unloaded stepper motor from a standstill without losing synchronism with the field and without overshooting to the next step when coming to a stop. instantaneous value - 1. The magnitude, at any particular instant, of a varying value. 2 The value of voltage or current at a particular instant. If the selected instant is the time when the polarity of the waveform changes, this value will be zero. instruction- 1. Information that, when properly coded and introduced as a unit into a digital computer, causes the computer to perform one or more of its operations. All instructions commonly include one or more addresses. 2. A binary code applied to a logic circuit to affect its mode of operation. 3. A statement that specifies an operation and the values or locations of its operands. In this context, the term instruction is preferable to the terms command or order, which are sometimes used synonymously. 4. A set of bits that defines a computer operation and is a basic command understood by the CPU. It may move data, do arithmetic and logic functions, control I/O devices, or make decisions as to which instructions to execute next. 5. In a computer, a single order within a program. This order will be fetched from memory, decoded, and executed by the CPU. Instructions may be arithmetic or logical, and operate on registers, memory, I/O devices, or specify control operations. A sequence of instructions is a program. 6. A machinelanguage command executed by the microprocessor in a computer system. instructional constant -Also called pseudoinstruction. In a computer, data stored in the program or instructional area that will be used only as a test constant. instruction code-The list of symbols, names, and definitions of the instructions that are intelligible to a given computer or computing system. instruction counter -A multiple-bit register that keeps track of the address of the current instruction. See control counter. instruction cycle-The process of fetching an instruction from memory and executing it. instruction deck-A set of punched cards containing a symbolic coded program to be read into a computer. instruction f e t c h -See fetch. instruction length-The number of words needed to store an instruction. It is one word in most computers,

379 but some will use multiple words to form one instruction. Multiple-word instructions have different instruction execution times depending on the length of the instruction. instructionmodification-A change in the operation-codle portion of a computer instruction or command such that, if the routine containing the instruction or command is repeated, the computer will perform a different operation. instriuction register- 1. In a computer, the register that temlporady stores the instruction currently being performed by the control unit of the computer. 2. A computer storage for the binary code for the operation to be performed. Usually this instruction represents the contents of the address just designated by the program counter. However, the contents of the instruction register or the program counter may be changed by the computations. This, of course, represents one ofthe key ideas of a storedprogram computer-instructions, as well as data, can be operated on and subsequent operations will be determined by the results. ertoire-The instruction set for a computer. instriuction set- 1. A means of describing computer capability. It consists of a listing of all the instructions the computer can execute. The basic operations that can be performed by a CPU. Necessary instructions are arithmetic, logical, test and branch, and moves. 2. The set of general-purpose instructions available with a given computer. In general, different machines have different instructilm sets. The number of instructions only partially indicates the quality of an instruction set. Some instructions may only be slightly different from one another; others rarely may be used. Instruction sets should be c0mpare.d using benchmark programs typical of the application to determine execution times and memory requirements. instruction storage-The storage medium that contains basic machining instructions in coded form. ~nstri~ction time -The time required to fetch an instructison from memory and then execute it. instriuction word -A computer word that causes the computer to execute a particular operation. See word. instrument -A device capable of measuring, recording, andlor controlling. ~ n ~ t approach ~ ~ ~ -A~ blind e ~ landing--.e., t solely by navigational instruments, without visual reference to the terrain. ~ ~ ~ ~ ~ i ~ system ~ e -In~ navigation, ~ - a a~ system furnishing vertical and horizontal guidance to aircraft during descent. Touchdown requires some other guidance. ~ n s % ~ ~ ~ ~-@1. ~ The t~ uset of i odevices n to measure the values of varying quantities, usually as part of a system for keeping the quantities within prescribed limits. 2. Adding code to a program for injecting data and collecting information, usually for dynamic analysis. ~ n ~ ~ r i ~ m e ~ amplifiertatjon High accuracy analog amplifier with full differential inputs and gains ranging from 1 to 1000. ~ n s % r i ~ ~ ebus~~aA t idedicated ~n bus tailored for the connection of measurement and control devices. ~ n s ~chopper r ~ ~- A e vibrating ~ ~ switch used for modulating, demodulating, and switching dc or lowfrequency ac information in instrumentation. It is driven synchronously from an ac or pulsating dc source. The driven switching circuit is designed for low-level (0- to 10-volt) signal information. ~ ~ s t r driver~ ~ ~ Software n t module that converts the parameters in the object code to the specific instruction sequence needed to stimulate an instrument.

instruction modification- insdated INSTRUMENTATION AMPLIFIER'S INVERTING INPUT

INSTRUMENTATIONAMPLIFIER'S NONINVERTING INPUT

R

+=(I+&>

Instrumentation amplifer.

instrument error-The inaccuracy of an instrument. instrument flight-A blind flight-Le., one in which the pilot controls the path and altitude of the aircraft solely by instrument. instrument lamp-A lamp that illuminates or irradiates an instrument. instrument landing station-A special radio station for aiding in landing aircraft. instrument landing system- Abbreviated ILS. A radionavigation system intended to aid aircraft in landing. It provides lateral and vertical guidance, including distance from the landing point. Consists of four ground radio transmitting stations at and in the vicinity of an airport, which radiate direction and position signals to approaching aircraft that are received on an instrument in the aircraft and alert the pilot to any deviation from the safe approach path to the correct touchdown point. instrument landing system localizer- System of horizontal guidance embodied in the instrument landing system that indicates the horizontal deviation of the aircraft from its optimum path of descent along the axis of the runway. instrument multiplier-See voltage-range multiplier. instrument relay-A relay that operates on the principles employed in such electrical measuring instruments as the electrodynamometer, iron-vane, and D' Arsonval meters. ~ ~ instrument o a ~shunth An internal or external resistor connected in parallel with the circuit of an instrument to extend its current range. instrument switch -A switch disconnecting an instrument or transferring it from o3e circuit or phase to another. instrument transformer -A transformer that reproduces, in its secondary circuit, the primary current (or voltage) with its phase relationship substantially preserved, suitable for utilization in measurement, control, or protective devices. instrument-transformer correction factorThe factor by which a wattmeter reading must be multiplied to correct for the effect of the instrument-transformer ratio correction factor and phase angle. instrument zero-The lower end of the measuring instrument's scale. Instrument zero may not coincide with zero value of the measured variable. Zero error is the error at instrument zero. insulated-Separated from other conducting surfaces by a nonconductive material offering a high, permanent resistance to the passage of current and disruptive discharge.

insulated carbon resistor - insulator 1OA 20A

PRIMARY 50A

1WA

380 f

Instrument transformers.

insulated carbon resistor -A carbon resistor encased in fiber, plastic, or other insulation. insulated clip-A clip terminating in an insulated eye through which flexible cords or wires may be run and supported. insulated enclosure-A special shielded enclosure design providing insulation against weather or providing maximum temperature stability. Usually prefabricated as an exterior building panel in modular construction. insulated-gate field-effect transistor- Abbreviated IGFET. In general, any field-effect transistor that has an insulated gate regardless of the fabrication process.

SUBSTRATE

PGATE

/ CONDUCTING CHANNEL

Insulated-gate field-effect transistor.

insulated-substrate monolithic circuit-An integrated circuit that may be either an all-diffused device or a compatible structure so constructed that the components within the silicon substrate are insulated from one another by a layer of silicon dioxide, instead of the reverse-biased pn junctions used for isolation in other techniques. insulated terminals- Solderless terminals provided with an insulated sleeve over the barrel to prevent a short circuit. insulated wire-A conductor covered with a nonconductive material. insulating material-1. A material on or through which essentially no current will flow. It is used to confine the flow of current within a conductor or to eliminate the shock hazard of a bare conductor. 2. Any composition primarily adapted for preventing the transfer of electricity therethrough, the useful properties of which depend on its chemical composition or atomic arrangement. insulating sleeve -Tube or tape of insulating material placed around metal-enclosed capacitors to insulate the case electrically from other components and wiring.

insulating strength -The measure of the ability of an insulating material to withstand electrical stress without breaking down. It is defined in terms of the voltage per unit thickness necessary to initiate a disruptive discharge and usually is measured in volts per centimeter. See also dielectric strength; electric strength. insulating tape-Tape that is wrapped around joints in insulated wires or cables. It is impregnated with an insulating material and covered with adhesive on one side. insulating varnish-A varnish applied to coils and windings to improve their insulation (and, at times, their mechanical rigidity). insulation- 1. A nonconductive material that prevents the leakage of electricity from a conductor, provides mechanical spacing or support, or protects against accidental contact. 2. The use of a material that passes negligible current to surround or separate a conductor to prevent loss of current. 3. A material that offers high electric resistance, making it suitable for covering components, terminals, and wires to prevent the possible future contact of adjacent conductors resulting in a short circuit. 4. Material used to cover electrical wires to prevent electrical leakage and short circuiting and to reduce the danger of shock. insulation displacement termination -A connector that has insulated wire is forced into a channel constructed so that ridges or teeth in the channel cut through or displace the insulation and make an air-tight contact with the wire. insulation piercing-A crimping method in which lances pierce wire insulation, enter into the strands, and make electrical contact without stripping the wire. insulation rating -The dielectric-strength and insulation-resistance values required to ensure satisfactory performance. insulation resistance- 1. The resistance offered by an insulating material to the flow of current resulting from an impressed dc voltage. 2. The ratio of the voltage applied between two electrodes in contact with a specific insulator to the total current between the electrodes. 3. Industrial specifications usually call for a certain minimum value (several thousand megohms) determined with a specific voltage applied. 4. The direct current resistance between the two terminals of a capacitor, or between either or both of the terminals and the capacitor case. 5. The ratio of dc voltage impressed across a capacitor to the resultant leakage current. For a particular capacitor design, the product of insulation resistance and capacitance (megohm-microfarad) is quite constant. 6. The electrical resistance of the insulating material (determined under specified conditions) between any pair of contacts, conductors, or grounding devices in various combinations. insulation resistivity -The insulation resistance per unit volume of insulation. insulation stress-The molecule separation pressure caused by a potential difference across an insulator. The practical stress on insulation is expressed in volts per mil. insulation s y s t e m -All of the insulation materials used to insulate a particular electrical or clcctronic product. insulator-1. A material in which the outer electrons are tightly bound to the atom and are not free to move. Thus, there is negligible current through the material when a voltage is applied. The resistivity is greater than 10' ohm-cm and generally decreases when the temperature rises. 2. A nonconducting substance such as porcelain, plastic, glass, rubber, etc. 3. A material of such low electrical conductivity that current through it can

38 1 usually be neglected. 4. A material of low electrical conductivity designed for supporting a conductor, physically and electrically separating it from another conductor or object. insulator arcing ring-A circular or oval metal p a t placed at one or both ends of an insulator to prevent current from arcing over and damaging it and/or the conductor. insulator arcover-The flow of power current over an insulator in the form of an arc following a surface discharge. insulazing -See surface insulation. insulectrics -The science encompassing insulating materials in electrical insulation. integer-A whole number, which may be positive, negative, or zero. It does not have a fractional part. Examples of integers: 1, 2, 48, -136, etc., but not 3.7 or 3/4. integral-cavity, reflex-klystron oscillator-A reflex-klystron oscillator in which tuning is accomplished by changing the physical dimensions of the resonant cavity. It is usually referred to as a diaphragm- or gridgap-tuned klystron, since a flexible diaphragm is used to change the cavity dimension, i.e., the gap between the cavity grids. integral circuit packages-Microcircuits assembled from discrete components and all circuits created essentially in an active or passive substrate. integral contact -Current-carrying member of jack, switch, or relay. Usually a flat, flexible spring or other conducting member having no separate contacts attached at point of mating. integral-external-cavity reflex oscillator-A reflex-klystron oscillator in which a fixed internal cavity is tightly coupled to a permanently attached external cavity. Tuning is achieved by varying a reactance probe in the external cavity. integral-horsepower motor-A motor that is built into a frame and has a continuous rating of 1 horsepower. integral resistor- An internal or external resistor preconnected to the electrical element and forming an integral part of the cup assembly to provide a desired electrical characteristic of a precision potentiometer. integrated-A type of design in which two or more basic cclmponents or functions are physically, as well as electrically, combined- usually on one chassis, such as an integrated amplifier. integrated amplifier -Also called, occasionally, a control amplifier, since it is an amplifier with controls. aimplifier that embodies in a common housing the preamplifier and control section and the power amplifier. Some e d y amplifiers of large power were in two separate units, one the control unit with preamplifiers and the other the power amplifier. 2. A single component combining the fplnctions and circuitry of a power amplifier and preamplifier. See also amplifier. integrated circuit -Abbreviated IC. Also called functional device. 1. An electrical network-active or passive-composed of two or more circuit elements inextricably bound on a single semiconductor substrate. To further define the nature of an integrated circuit, additional modifiers may be prefixed. Examples: dielectric-isolated motaolitlhic integrated circuit, beam-lead monolithic integrated circuit, or silicon-chip tantalum thin-film hybrid integrated circuit. See aZso film integrated circuit; hybrid integrated circuit; monolithic integrated circuit; multichip integrated circuit. 2. Any electronic device in which both active and passive elements are contained in a single package. The term frequently is used for circuits other than those containing semiconductors; for example, microwave

insulator arcing ring

- integrated morphology

designers consider many types of waveguide assemblies to be integrated circuits. 3. A small chip of solid material (generally a semiconductor) upon which, by various techniques, an array of active and/or passive components has been fabricated and interconnected to form a functioning circuit. Integrated circuits, which are generally encapsulated with only input, output, power supply, and control terminals accessible, offer great advantages in terms of small size, economy, and reliability. 4.The physical realization of a number of electrical circuit elements inseparably associated on or within a continuous body of semiconductor material to perform the function of a circuit. 5. An electronic device containing several elements, active or passive, that perform all or part of a circuit function. 6. An interconnected array of conventional components -transistors, diodes, capacitors, and resistors -fabricated in situ within and on a single crystal of semiconductor material with the capability of performing a complete electronic circuit function. 7. An electronic circuit containing transistors, diodes, resistors, and perhaps capacitors and photocells, along with interconnecting electrical conductors processed and contained entirely within a single chip of silicon. 8. Multiple, interconnected circuit elements, contained on or in a common substrate, that function as a unit and not separately. integrated-circuit array- Multiple integrated circuits formed on a common substrate and electrically interconnected during fabrication. integrated-circuit p a c k a g e -The combined mounting and housing for an integrated circuit; the package protects the integrated circuit and pennits external connections to be made to it, integrated communication system -Communication system on either a unilateral or joint basis in which a message can be filed at any communications center in that system and be delivered to the ad&essee(s) by any other appropriate communication center in that system without reprocessing en route. integrated component-A number of electrical elements comprising a single structure that cannot be divided without destroying its stated electronic function. integrated console -Computer control console that is capable of controlling the operation of the switching center equipment d an integrated communications system. integrated data processing -A method of transforming disjointed and repetitive paperwork tasks into a correlated and mechanized production of information for any purpose. integrated electronic c o m p o n e n t -Abbreviated IEC. An assembly that consists of several integrated circuits interconnected on a single chip of silicon bo provide a complete electronic function with a circuit content greater than 10 equivalent gates. integrated electronics-That portion of electronic art arid technology in which the interdependence of material, device, circuit, and system-design considerations is especially significant; more specifically, that portion of the art dealing with integrated circuits. integrated electronic s y s t e m -See integrated circuit. integrated equipment components-Abbreviated IECs. Integrated-circuit chips that contain a complete logic function. integrated injection logic-See 1%. integrated microcircuit -See integrated circuit. integrated morphology -The structural characterization of an electronic component in which the identity of the current- or signal-modifying areas, patterns, or volumes has become lost in the integration of electronic

integrated optical circuit - intelligent terminal materials, in contrast to an assembly of devices performing the same function. integrated optical circuit -Abbreviated IOC. Also called optical integrated circuit. A circuit, or group of interconnected circuits, consisting of miniature solidstate optical components, such as light-emitting diodes, optical filters, photodetectors (active and passive), and thin-film optical waveguides on semiconductor or dielectric substrates. integrated optics- The interconnection of miniature optical components via optical waveguides on transparent dielectric substrates, using optical sources, modulators, detectors, filters, couplers, and other elements incorporated into circuits analogous to integrated electronic circuits, for the execution of various communication, switching, and logic functions. integrated services digital network- Abbreviated ISDN. A switched network providing end-toend digital connectivity for simultaneous transmission of voice and data over multiplexed communications channels. See also ISDN. integrated software-An applications software package containing programs to perform more than one function. integrated transducers -Semiconductor components that change the form of energy (e.g., piezoelectric devices, photogenerators, thermistors, etc.) and that are integrated into multifunction chips. integrated voltage regulator -Abbreviated IVR. An integrated structure that serves as the reference, error amplifier, and shunt elements for shunt voltage regulation. A resistive voltage divider connected to its input provides adjustment of the output voltage. integrating circuit -See integrator, 1.

R

-3-Y T

E'N

382 Thus, the angle of rotation of the shaft is proportional to the time integral of the input signal. integrating p h o t o m e t e r -A photometer that, with a single reading, indicates the average candlepower from a source in all directions or at all angles in a single plane. integrating relay-A relay that sums up the inputs of voltage or current supplied to it and opens or closes its contacts in response to the input so integrated. integrating-sphere densitometer -A photoelectric instrument that measures the density of motion-picture film or its sound track. integration time-That time during which all electrons formed by impinging photons are gathered in a potential well under an energized electrode. integrator- 1. A device with an output proportionate to the integral of the input signal. 2. In certain digital machines, a device that numerically approximates the mathematical process of integration. 3. A device that determines on a continuous basis the total value of a quantity being measured, usually as a function of time. 4. Device for summing or totalizing counts, areas under curves, etc.

Integrator.

OUT

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+

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Formula.

Integrating circuits.

integrating meter-A meter that adds up (integrates) the electrical energy used over a period of time. An ordinary electric watthour meter is an example. integrating motor -A motor that maintains a constant ratio of output-shaft rotational speed to input signal.

intelligence bandwidth-The total audio (or video) frequency bandwidths of one or more channels. intelligence sample-Part of a signal taken as evidence of the quality of the whole. intelligence signal -Any signal that conveys information (e.g., voice, music, code, or television). intelligent controller- Device controller equipped with local interpreting functions, such as editing, input validity checks, and complex command decoding. intelligent instruments-Devices that possess capabilities that raise them above the level of instruments that merely sense and display analog information. The following list presents one instrument intelligence rating system, from the lowest order of intelligence to the highest: 1. The ability to sense and display information. 2. Conversion of analog information into digital. 3. Mathematical manipulation of digital data. 4. Interpretation of results of mathematical manipulation. 5. Making of decisions on the basis of interpretation. intelligent robot-A robot that can make decisions by itself through its sensing and recognizing capabilities. intelligent terminal -1. An input/output device in which a number of computer processing characteristics are physically built into, or attached to, the terminal unit. 2. Programmable control terminal that drives other terminals, peripherals, floppy disks, machines, program counters, etc. 3. A programmable data service, usually

intelligent time-division multiplexer - interactive environment

383

remote from the main computer, that unburdens the host computer by performing preliminary data processing such as formatting, verification, or validation. 4. A terminal that has editing and block-transmission capabilities, which allow manipulation of data in the terminal before transmission to the host computer. Some intelligent termiuals can also perform checks on entered data. An intelligent terminal’s programmability is restricted to formatting data on its screen. These formats can be called up through the keyboard and can have protected fields that allow entering of data (numeric, alphabetic, or alphanumeric) in the prescribed format. User programmability distinguishes the intelligent terminal from its less intelligent relatives. In addition to this programmability, an intelEgent terminal has editing functions similar to those of a smart terminal. 5. An input/output device with built-in intelligence in the form of a microprocessor and able to perfom functions that would otherwise require the central computer’s processing power; sometimes called a standalone terminal. 6. A terminal with local processing power whose clharacteristics can be changed under program control. intelligent time-division multiplexer-See ITDM. intelligent voice terminal-Intelligent terminal operated by the human voice; software resident in the tenninal is user-programmable. Best for applications suiting an intelligent terminal but where hands-free data entry is cost advantageous. inteIIi gibi Iity -See articulation. INTELSAT -Abbreviation for International Telecommunications Satellite Consortium. 1. A series of commercial communications satellites designed to relay telephony and television signals among the member INTELSAT nations. The INTELSAT global network employs an equatorial orbibit above the Atlantic, Pacific, and Indian Oceans. Satellites in these three locations are capable of linking virtually all the inhabited areas of the world. 2. International (primarily noncommunist) satellite agency whose member nations lease transponder capacity on its satellite system to provide at least some TV in all parts of the world.

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GLOBAL HORN

INTELSAT satellite.

interisif ier electrode-Also called postaccelerating electrode. In some types of electrostatic cathode-ray tubes, an elecrsode that permits additional acceleration of the

electron beam after it has been deflected. This electrode emits greater intensity of the trace without materially reducing the deflection sensitivity of the tube. intensifying screen -A thin fluorescent screen placed next to a photographic plate to increase the effect of radiation on the plate. intensitometer- Also called a dosage meter or dosimeter. An instrument that estimates the amount of X-ray radiation, for determining the duration of exposure during X-ray pictures or therapy. intensit)- 1. The strength of a quantity. 2. The relative strength, or amplitude, of electric, magnetic, or vibrational energy. 3. The brilliance of an image on the screen of a cathode-ray tube. 4. The strength of light or other electromagnetic energy being radiated or reflected per steradian. 5 . The flux per unit solid angle radiating (diverging) from a source of finite area. intensity control -Used with cathode-ray tubes to control the intensity of the electron beam and hence the amount of light generated by the fluorescent screen. Generally, the grid bias of the tube is regulated. intensity level-Ratio of the intensity of the sound to a reference intensity of a free plane wave of 1 microwatt per square centimeter under normal conditions. Commonly expressed in decibels. intensity modulation- 1. The process andor effect of varying the electron-beam current in a cathode-ray tube, resulting in varying brightness or luminance of the trace. 2. The process in which the electron beam of a cathode-ray tube is varied in intensity in accordance with the magnitude of the signals it receives. See also Z-axis modulation. intensity of radiation -The radiant energy emitted in a specified direction per unit time, per unit area of surface, per unit solid angle. interaction -The effects two or more parts, components, etc., have on each other while each is performing a function. interaction crosstalk-Crosstaik resulting from mutual coupling between two paths by means of a third path. For example, if a signal on pair 1 is coupled bo pair 2, and then coupled from pair 2 to pair 3, where it is measured, it is known as interaction crosstalk. interaction loss (of a transducer) -Expressed in decibels, it equals 20 times the logarithm (to the base 10) of the scalar value of the reciprocal of the interaction factor. interaction space-In an electronic tube, the region where the electrons interact with an alternating electromagnetic field. interactive- 1. Pertaining to an application in which each entry elicits a response. An interactive system may also be conversational, implying continuous dialog between the user and the system. 2. A program or system that can ask questions of the user and then take action based on his response. Conversational is often used to mean the same thing. 3. Refers to those applications in which a user communicates with a computer program via a terminal, entering data and receiving responses from the computer. 4. Processing of data on a two-way basis, with human intervention redirecting the processing in a predetermined manner. interactive d e b u g g e r -A computer system software utility that permits a user to examine his or her task while it executes by stopping it at given points (usually called breakpoints) and displaying and changing memoryhegister contents. interactive environment-A situation in which a computer continually responds to the user on receipt of directives from his or her tenninal.

interactive graphics - interdigitaltransducer interactivegraphics- 1. The use of a large-screen, high-precision CRT and its associated circuitry -usually linked to a large-scale computer system through a small control computer -on which both alphanumeric and vector data are displayed and manipulated. By using the data entry device, two- and three-dimensional geometric designs can be created, deleted, and modified in real time to achieve desired results. 2. The use of a display terminal in a conversational or interactive mode. 3. Capability to perform graphics operations directly on the computer with immediate feedback. interactive operation-Also called conversational mode. Online operation in which there is a give-and-take between person and machine. interactive system-1. A system in which it is possible for the human user or the device serviced by the computer to communicate directly with the operating program. For human users, this arrangement is termed a conversational system. 2. A system in which a computer or operating program communicates bilaterally with a user. interactivity- Computer programs, online services, and interactive TV in which the user can make inputs that direct subsequent delivery of services. Channel surfing is a crude form of interactivity. Internet and online services provide simple forms of interactivity, i.e., point-and-click. interaxis error- The deviation from 90" perpendicularity of one set of resolver windings when excitation is applied to one of the other windings. For rotor interaxis error, one stator winding is excited; for stator interaxis error, one rotor winding is excited. interbase current-In a junction tetrode transistor, the current that flows from one base connection to the other through the base region. interbase resistance-Resistance between base 2 and base 1 of a unijunction transistor measured at a specified interbase voltage with I E = 0. interblock space-See IRG. intercarrier noise suppression-The means of suppressing the noise resulting from increased gain when a high-gain receiver with automatic volume control is tuned between stations. The suppression circuit automatically blocks the audio-frequency output of the receiver when there is no signal at the second detector. intercarrier sound system -A television receiving system in which use of the picture carrier and the associated sound-channel carrier produces an intermediate frequency equal to the difference between the two carrier frequencies. This intermediate frequency is frequency modulated in accordance with the sound signal. intercellularmassage-The ultrasonic stimulation of body cells. Sometimes called micromassage. intercepting-Routing of a call or message placed for a disconnected or nonexistent destination to an operator position or a specially designated terminal or machine answering device. interceptingtrunk-A trunk to which a call made to a vacant number, a changed number, or a line out of order is connected so that action may be taken by an operator. intercept operator- The telephone operator who requests the number called, determines the reason for the intercept, and relays the information to the calling party. intercept receiver- Also called search receiver. A specially calibrated receiver that can be tuned over a wide frequency range in order to detect and measure enemy rf signals. intercept service -In a telephone system, a service provided to subscribers whereby calls to disconnected stations or dead lines are either routed to an intercept operator for explanation or the calling party receives a distinctive tone signal or recorded announcment to indicate that he or she has made such a call.

384 intercept tape-A tape used for temporary storage of messages intended for trunk channels and tributary stations in which there is equipment or circuit trouble. intercept trunk-See intercepting trunk. intercharacter space-In telegraphy, the space between characters of a word. It is equal to three unit lengths. intercom-See intercommunication system. intercommunicationapparatus-Equipment and systems for paging and intercommunication within a building, including audio, bell systems, pillow systems, and pocket page systems. intercommunicationsystem -Also called intercom. 1. A two-way communication system without a central switchboard, usually limited to a single vehicle, building, or plant area. Stations may or may not be equipped to originate a call, but can answer any call. 2. A system that permits selective speaker voice communication via wires between any pair of several stations, usually in the same building. The stations may be either master stations, which may initiate calls to any of a group of stations, or slave stations, which may initiate calls only to their master station. 3. A communication system that bridges the gap between a regular telephone system and the public address (PA) system it locates people and permits communication with them. Most often, it is installed as an adjunct to telephone and PA systems. intercom wire- Wire used to connect communications instruments, telephones, telegraph, etc. interconnecting wire- 1. Wires used for connections between subassemblies, panels, chassis, and remotely mounted devices. Does not necessarily apply to the internal connection of these units. 2. The physical wiring between components (outside a module), between modules, between units, or between larger portions of a system or systems. interconnection-1. Also called tie line. A transmission line connecting two electric systems or networks and permitting energy to be transferred in either direction. Larger interconnections are often called interties, giant ties, or regional interconnections. 2. The conductive path required to achieve connection from a circuit element to the rest of the circuit. 3. Also called intraconnection. The physical wiring between components (outside a module), between modules, between units, or between larger portions of a system or systems. interconnection diagram-Diagram showing the identity of all units in a piece of electronic equipment and the connections between them. interconnections (microelectronic) -Those conductors and connections that are not in continuous integral contact with the substrate or circuit elements of an integrated circuit. interconnectionsystem -The electrical and mechanical interconnection of any one or all of the six levels of interconnections generally common to electronic equipment. The six levels of interconnection are intramodule, module to motherboard, intramotherboard, motherboard to back panel, backpanel wiring, and input/output. interdiction-Techniques to prevent nonsubscribers access to informationiprograms on cable or drop cables. Interdiction electronics are outside the consumer's house and can be addressable. interdigital magnetron-A magnetron with anode segments around the cathode. Alternate segments are connected together at one end, and remaining segments at the opposite end. interdigital transducer- Abbreviated IDT. A number of interleaved metal electrodes whose width and spacing is equal and uniform throughout the transducer pattern. When a harmonic voltage is applied

385 to the transducer terminals, the IDT pattern excites a periodic electric field that penetrates into the piezoelectric substrate. The substrate responds by periodically (expanding and contracting in unison with these fields. With the proper choice of substrate orientation, this piezoelectric excitation gives rise to surface acoustic waves that propagate in the two directions normal to the IDT electrodes. The electric field can be produced by applyling signals of opposite potential to two parallel metal electrodes formed in films deposited on the surface of the cirystal. As the field is applied, the alternating signals send an acoustic wave across its surface; this wave is reconverted to an electric signal at a second pair of similar electrodes at the other end of the crystal. In practice, the transducer consists of several pairs of intehaved parallel electrodes, which give the transducer its name. The fingers, and the space between them, must be related to the size of a wave of the frequency desired. In certain applications the transducer fingers are less than a thousandth of a millimeter wide. interelectrode capacitance- The capacitance between one electron-tube electrode and the next electrode toward the mode. The capacitance between the electrodes in an electron tube. intertclectrode coupling -Capacitive feedback from the plate of a tube to the grid. In triodes, this limits the maximum amplification possible without starting oscillation. interelectrode leakage-The undesired current that flows between elements not normally connected in any way. intercsllectrode transit time-The time required for an electron to travel between two electrodes. intercekment capacitance-The capacitance caused by the pn junctions between the regions of a transistor and measured between the external leads of the transistor. intenexchange channel -A channel connecting two different exchange areas. interface-I. A point or device at which a transition between media, power levels, modes of operation, etc., is imde. 2. The two surfaces on the contact sides of mating connectors that face each other when mated. 3. A cornmon boundary between two or more items. May be mechanical, electrical, functional, or contractual. 4. A common aspect at tbe boundary between two systems involving intersystem communication- eg., the interaction between research and development, basic and applied science, or engineering and systems development. 5. The physical and space boundary surrounding the system, subsystem, equipment, or component, through which all environmental and operational stimuli essential to the device or affecting its proper operation must propagate or interact with other related devices or structures. 6. The hardware for linking two units of electronic equipment; for example, a hardware component to link a computer with its input (or output) device. 7. The means of connection between two logic elements, often elements that belong to two different “families.” 8. The hardware or software required to be able to communicate with, sense, or control external equipment 9. A circuit that controls the flow and format of data between a computer and a terxninal or other peripheral. 10 An electrical connection that permits a peripheral device or communications channel to be attached to a system. 11. An electronic assembly that ties an external device to a computer. 12. A common boundary between automatic data-processing systems or parts of a single system. In communications and data systems, it may involve code. format, speed, or other changes as required. 13. The junction or point of interconnection between two systems or equipments with Werent characteristics. They may differ with respect to voltage, frequency, operating speed.

interelectrode capacitance

- interface system

type of signal, andlor type of information coding. 14. To interconnect different systems to resolve their incompatibilities. 15. A common or shared boundary between two or more instruments, devices, or systems, which enables exchange of information among interconnecting units or systems that may not be directly compatible. interface adaptor- Also called device adaptor. A unit that provides a mechanical and electrical interconnection between the tester and the device under test. It may include special stimulus, measurement, load, and switching circuitry unique to a device or family of devices but which is not provided in the tester. interface analysis-Checking the interfaces between program elements (modules) for consistency and proper data transfer. interface card-A device that converts a computer UO bus into some standard YO confi,wation (8- or 16-bit parallel BCD, RS-232, IEEE 488, etc.). interface circuit -1. A circuit that links one type of logic family with another or with analog circuitry. 2. A circuit that allows two or more systems to be readily joined or associated. Examples include circuits that link linear and digital systems and those that enable communication between two circuits through a transmission line. 3. A circuit that links one type of device with another. Its function is to produce the required current and voltage levels for the next stage of circuitry from the previous stage. 4. An input/output circuit that permits different chips to communicate over a bus. 5. Linear or analog circuit with the prime function of supporting digital circuitry. Employed where the digital circuitry for the world of data processing and computation must meet the physical world of analog variables. Also used to mix functions from a number of digital logic families to obtain performance or economic benefits. There are at least nine different categories of interface circuits: bus interface, memory interface and control, line drivers and receivers, peripheral interface, numeric display interface, data converters, voltage reference, voltage comparators, and communications interface.

LOW CURRENT I N

HIGH CURRENT OUT

iAz2iy CONVERTER TRANSOUCERtSENSOR ANALOG SIGNAL IN

DIGITAL SIGNAL . .OUT

DIGITAL SIGNAL IN

ANALOG SIGNAL OUT

Interface circuits. interface c o n n e c t i o n -Also called feedthrough. A conductor that connects patterns on opposite sides of a printed circuit board. interface equipment-Equipment used between two other equipments that would otherwise be incompatible. interface resistance -See cathode interface. interface system -The device-independent mechanical, electrical, and functional elements of an interface necessary to effect communication among a set of devices. Cables. connector, driver and receiver circuits, signal

interface unit

- interlaced scanning

lines, descriptions, timing and control conventions, and functional logic circuits are typical interface system elements. interface unit- A device that translates incoming signals that are incompatible with the electrical characteristics of the computer without changing the information content. Also translates outgoing signals for the benefit of associated equipment that is designed to different electrical standards. interfacial bond -An electrical connection between the two faces of a substrate. interfacial connection -In a printed circuit board, a conductor that connects conductive patterns on opposite faces of the base. interfacial junction -The junction that is formed by the faces of the two mating halves of a connector. This junction can be tightly compressed or loose, depending on the requirements of the application of the connector. interfacial seal -Sealing of a mated connector pair over the whole area of the interface to provide sealing around each contact. This is usually done by providing a soft insert material on one or both halves of the connector, which are in compression when mated. interfacing -1. The joining of members of a group (people, instruments, and so on) in such a way that they are able to function in a compatible (synchronized) and coordinated fashion. 2. Interconnecting a program counter with its application devices and data terminals through various modules and cables. Interface modules convert program counter logic levels into external signal levels, and vice versa. interference -1. Any electrical or electromagnetic disturbance, phenomenon, signal, or emission, man-made or natural, which causes or can cause undesired response, malfunctioning, or degradation of the electrical performance of electrical and electronic equipment. 2. Any signal that degrades the accuracy of a system. Interfering signals may be separated into two classes: damaging and degrading. Damaging signals cause degradation of accuracy after the signal is removed (even permanently). 3. Any undesired electrical signal induced into a conductor by electrostatic or electromagnetic means. 4. The additive process whereby the amplitudes of two or more overlapping waves are systematically attenuated and reinforced. 5. The process whereby a given wave is split into two or more waves by, for example, reflection and refraction of beam splitters, and then possibly brought back together to form a single wave. 6. Extraneous energy that tends to interfere with the desired signal. 7. Unwanted occurrences on communication channels that result from natural or human-made noises and signals. interference blanker-A device used with two or more pieces of radio or radar equipment to permit simultaneous operation without confusion of intelligence, or used with a single receiver to suppress undesired signals. interference eliminator-A device designed for the purpose of reducing or eliminating interference. interference fading -Fading produced by different wave components traveling slightly different paths in arriving at the receiver. interference filter-A device added between a source of human-made interference and a radio receiver to attenuate or eliminate noise signals. It generally contains a combination of capacitance and inductance. interference guard band-See guard band. interference pattern - 1. The resultant space distribution of pressure, particle velocity, or energy flux when progressive waves of the same frequency and kind are superimposed. 2. The pattern produced on a radar scope by interference signals.

386 interference prediction -Estimation of the interference level of a particular item of equipment with respect to its future electromagnetic environment. interference-rejection unit -Abbreviated IFRU. A tunable filter or wave trap capable of being adjusted to reject any frequency within the IF passband of a receiver while allowing the remainder of the passband curve to remain intact. It is adjusted to reject an interference signal and thus constitutes a form of antijamming. interference source suppression -Techniques applied at or near a source of radiation to reduce its emission of undesired signals. interference spectrum -The frequency distribution of the jamming interference in the propagation medium external to the receiver. interferometer -An apparatus that shows interference between two or more wave trains coming from the same luminous area, and also compares wavelengths with observable displacements of reflectors or other parts. interferometer homing -A homing guidance system in which the direction of the target is determined by comparing the phase of the echo signal as received at more than one antenna. interferometersystem -A method of determining the azimuth of a target through use of an interferometer to compare the signal phases at the output terminals of two antennas receiving a common signal from a distant source. intergranular corrosion -A localized attack at metallic grain boundaries due to the presence of impurities and/or mechanical stress. On exposure to corrosive catalysis, the grain boundaries become anodic and the grains cathodic. interior label-In a computer, a magnetically recorded sequence added to a tape to identify the contents. interior-wiring-system ground -The ground connection to one of the current-canying conductors of an interior wiring system. interlace- 1. In a computer, to assign successive storage location numbers to physically separated storage locations on a magnetic drum. This serves to reduce access time. 2. To transmit different interrogation modes on successive sweeps. interlaced scanning -Also called line interlace. 1. A system of scanning whereby the odd- and evennumbered lines of a picture are transmitted consecutively as two separate fields. These are superimposed to create one frame, or complete picture, at the receiver. The effect is to double the apparent number of pictures and thus reduce flicker. 2. A scanning process in which the distance from center to center of successively scanned

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1

END OF FIELD 1

Interlaced scanning.

END OF FIELD 2

interlace factor

387

- intermediate-frequency transformer-lead color code

lines is two or more times the nominal line width, and in which the adjacent lines belong to different fields. interlace factor-A measure of the degree of interlace of normally interlaced fields. interlace operation-A type of computer operation in which data can be read out of or copied into the memory without causing interference to the other activities of the computer. See also interrupt; time sharing, 1. interlacing-A method of scanning used in television, in which each picture is divided into two or more complete sets of interlacing lines to reduce flicker. interlayer connection-An electrical connection between conductive patterns in different layers of multilayer printed board. See through connection. interleave- 1. In a computer, to insert segments of one program into another program so that the two programs can be executed essentially simultaneously. 2. See interlace. interleaving-1. Placing between. For example, in ithe transmission of a composite color signal, the bands of energy of the chrominance signal are interleaved with, or !placed between, those of the luminance signal. 2. Assigning successive memory locations to different physical memory modules, interlock-A device actuated by the operation of some other device with which it is directly associated, to govern succeeding operations of the same or allied devices. Ihkrlocks may be either electrical or mechanical. interlock circuit-A circuit in which a given action cannot oi:cur until after one or more other actions have taken place. The interlocking action is generally obtained through the use of relays. interlocking-The forcing of a voltage of one frequency to be in step with a voltage of another frequency. interllock relay-1. A relay in which one armature cannot move or its coil be energized unless the other armature is in a certain position. 2. A relay with two sets of coils and respective armatures and contacts, so arranged that movement of one armature or energizing of its coil is dependent on the position of the other armature. interlock switch-A safety switch that deenergizes a high-voltage supply when a door or other access cover is opened. intermediate code-Machine input in a form between source and machine code; for example, pseudocode. intermediate current -The range of current (milliamperes) at which formulation of carbonaceous material may significantly affect contact resistance. intermediate fluxes-Hues consisting of mild organic acids and certain of their derivatives, such as the hydrohalides. As a class, they are weaker than the inorganic salt types.

intermediate frequency-Abbreviated IF. 1. A frequency to which a signal wave is shifted locally as an intermediate step in transmission or reception. 2. The fixed frequency resulting from heterodyning (i.e., beating or modulating to develop the s u m or difference frequency signal) the incoming signal with a signal from the local oscillator. The IF used in PM tuners is commonly 10.7 MHz, and in AM tuners is 455 IrHz. The IF signal is amplified in the IF channel, and it is here where most of the selectivity is introduced by tuned bandpass transformers and/or crystal or ceramic filters. 3. In superheterodyne receiving systems, the frequency to which all selected signals are converted for additional amplification, filtering, and eventual detection. intermediatefrequencyamplifier- 1, An amplifier tuned to a fixed frequency, or capable of single-control tuning over a range of frequencies, for che purpose of selectmg one of the frequency components generated in a mixer circuit. 2. The central stages of a superheterodyne radio receiver that amplify the signals after they have been converted to a fixed intermediate frequency by a mixer (frequency converter). intermediate-frequency harmonic interference -Interference caused in superheterodyne receivers by the radio-frequency circuit accepting ~ O I ? G X of the intermediatefrequency signal. intermediate-frequency interference ratioSee intermediate-frequency response ratio. intermediate-frequency jamming-A form of jamming in which two cw signals are transmitted at frequencies separated by an amount equal to the center frequency of the IF amplifier in the radar receiver. intermediate-frequency response ratio-Also called intermediate-frequency interference ratio. In a heterodyne receiver, the ratio of intermediate-frequency signal input at the antenna to the desired signal input for identical outputs. intermediate-frequency strip- Also called IF strip. A subassembly containing the intermediate-frequency stages in a receiver. intermediate-frequency transformer-Also called IF transformer. A transformer designed for use in the intermediate-frequency amplifier of a superheterodyne receiver. intermediate-frequency transformer-lead color code-Transformer leads in many radio receivers are identified by the following standard EIA colors: Blue: Plate Green: Grid or diode Black Grid return Red B + Green-black Second diode (full-wave transformers only)

i

455 kHz

@ INPUT

I

,

1

1

+

Intermediate-frequency ampli$er.

I ,

+ “cc

intermediate horizon

- internal correction voltage

intermediate horizon -A screening object (such as a hill, mountain, ridge, building, etc.) similar to the radar horizon but nearer to the radar site. For example, a distant mountain range might be the radar horizon on a given azimuth, while a nearer, lower ridge might screen a valley between it and the mountain range; the ridge would be an intermediate horizon. intermediate means- All system elements needed to perform distinct operations in the measurement sequence between the primary detector and the end device. intermediate repeater-A repeater used other than at the end of a trunk or line. intermediate state -The partial superconductivity that occurs when a magnetic field of appropriate strength is applied to a sphere of material below its critical temperature (i.e., the temperature below which the material would superconduct if no magnetic field were present). intermediate storage-The portion of the computer storage facilities in which information in the processing stage usually is stored. intermediate subcarrier- A carrier used for modulating a carrier or another intermediate subcarrier. It also may have been modulated by one or more subcarriers. intermediate switching region-In a relay, an area between low level (including dry circuit) and power switching (including full rated load) where the contact arc does not destroy deposits that are byproducts of the switching function. intermediate t r u n k distributing frame-A frame in which are mounted terminal blocks for connecting linefinders and first selectors. intermetallic bond -The ohmic contact made when two metal conductors are welded or fused together. intermetalliccompound-A compound of two or more metals that has a characteristic crystal structure that may have a definite composition corresponding to a solid solution, often refractory. intermittent -1. Occurring at intervals. 2. Electrical connections when conducting paths alternately open and close at some essentially uncontrolled rate. (Intermittents are undesirable since continuous connections are normally required.) 3. Not continuously present; disappearing and reappearing. intermittent current -A unidirectional current that is interrupted at intervals. intermittent d e f e c t -A defect that depends on variable conditions in a circuit. Hence, it is not present at all times. intermittent duty-Operation for specified alternate intervals of load and no-load; load and rest; or load, noload, and rest. intermittent-duty rating -The output rating of a device operated for specified intervals rather than continuously. intermittent-duty relay-A relay that must be deenergized at intervals to avoid excessive temperature, or a relay that is energized at regular or irregular intervals, as in pulsing. intermittent pulsing -The transmission of short bursts of radiation at irregular intervals. intermittent rating -The permissible output of a piece of apparatus when it is operated for alternate periods of load and rest that have a definite ratio to each other, or when it is run for a stated period of time that is not long enough to produce the final temperature. intermittent reception -A defect in which the receiver operates normally for a while, at regular or irregular intervals. intermittent scanning-One or two 360" scans of an antenna beam at irregular intervals to make detection by intercept receivers more difficult.

388 intermittent-service area- An area still receiving the ground wave of a broadcast station, but subject to interference and fading. intermod -Abbreviation for intermodulation distorInterference that results when strong signals tion (IMD). from a nearby transmitter mix with the desired signal in a radio receiver. intermodulation -Sometimes called intermod. 1. In a nonlinear transducer element, the production of frequencies corresponding to the sums and differences of the fundamentals and harmonics of two or more frequencies transmitted through the transducer. 2. An error form that occurs in chopper-stabilized amplifiers when a beat component forms between the chopper drive frequency and normal signals that have frequencies near that of the chopper. 3. Mixing of two radio signals to produce a third signal that interferes with the reception of a desired signal. intermodulation distortion -Abbreviated IMD. 1. Nonlinearity characterized by the appearance of frequencies in the output equal to the sums and differences of integral multiples of the component frequencies in the input signal. (Harmonics are usually not included.) 2. The introduction of unwanted signal energy as the result of interaction between two or more simultaneously reproduced tones, causing a smearing or veiling of the sound. All recording and amplifying equipment produces a certain amount of intermodulation distortion. but it can be held to sufficiently low levels to be below the threshold of audibility. 3. An analog-line impairment in which two frequencies interact to create an erroneous frequency, which in turn distorts the data-signal representation. 4. The production of spurious frequencies, not present in the original sound, that result from the interference or interaction of two (or more) sound signals that simultaneously occur in the original. These generally are sum and difference frequencies. For example, a 200-Hz and 75-Hz signal may occur at the same instant. If the equipment is prone to intermodulation distortion, these two may interact to produce a spurious 125-Hz tone. 5. The distortion caused by the addition of sum and difference modulation products when a complex wave (composed of two or more sine waves) passes through a nonlinear circuit. (When the modulation products are few, distortion is created; when they are many, noise is created.) 6. Distortion that results when two or more pure tones produce new tones with frequencies representing the sum and difference of the original tones and their harmonics. intermodulation frequencies-The sum and difference frequencies generated in a nonlinear element. intermodulation interference -The combinationfrequency tones produced at the output by a nonlinear amplifier or network when two or more sinusoidal voltages are applied at the input. Generally expressed as the ratio of the root-mean-square voltage of one or more combination frequencies to that of one of the parent frequencies measured at the output. intermodulation noise -Noise introduced in the channel of interest by signals being transmitted in other channels. internal arithmetic -Any computations performed by the arithmetic unit of a computer, as distinguished from those performed by peripheral equipment. internal calibration -Calibration by an internal voltage source (provided with the instrument) rather than an external standard. internal connection- Abbreviated IC. In a vacuum tube, a base-pin connection designed not to be used for any circuit connections. internal correction voltage -The voltage added to the composite controlling voltage of an electron tube.

389

internal graticule

It is the voltage equivalent of those effects produced by initial electron velocity, contact potential, etc. internal graticule-A graticule whose rulings are a permanent part of the inner surface of the cathode-ray tube faceplate. internal input impedance-The actual impedance at the input terminals of a device. internally caused contact chatter-That chatter resulting from the operation or release of the relay. It may be classified as initial, armatmeimpact, armature rebound, or armatwehesitation chatter. internally stored program -A sequence of instructions (program) stored inside a computer in the same storage facilities as the computer data, as opposed to being stored externally on punched paper tape, pin boards,etc. internal magnetic recording -Storage of information within the material itself, such as used in magnetic cores. internal memory- Also called internal storage. The total memory or storage that is automatically accessible to a computer. It is an integral physical part of the computer and is directly controlled by it. internal node-A junction between internal logic elements within an integrated circuit. internal output impedance-The actual i m p dance at the output terminals of a device. internal photoelectric effect-The creation of free electrons within a solid by the absorption of a sufficient amount of photons. The effect produces an increase in the conductivity of the solid. internal resistance-1. The effective series resistance in a source of voltage. 2. The resistance of a voltage source, such as a generator, battery or power supply, which acts to reduce the terminalvoltage of the source as current is drawn. internal storage-Also called main memory and core memory. 1. Storage facilities in a computer forming an integral physical part of and directly controlled by the computer. 2. The total storage automatically available to the computer. See also internal memory. internal timer-In a computer, the internal clock equipped with multiple registers that can monitor the duration of external events or generate a pulse after a fixed time. international broadcast station -A station licensed for transmission of broadcast programs for international public reception. By international agreement, f r e quencies are allocated between 6000 and 26,600 kHz. International call sign -The identifying letters and numbers assigned to a radio station in accordance with the International Telecommunications Union. The first character, or the first two, identify the nationality of the station. international code signal-A code, adopted by many nations for international communication, in which combinations of letters are used in lieu of words, phrases, and sentences. international communication service-A telecommunication servicebetween offices or stations (including mobile) belonging to different countries. international control station-A fixed station in the Fixed public Control Service, directly associated with the International Fixed Public Radio Communication Service. international coulomb-The quantity of electricity passing any section of an electric circuit in 1 second when the current is 1 international ampere. One international coulomb equals 0.99985 absolute coulomb. international farad-The capacitance of a capacitor when a charge of 1 intemational coulomb produces a potential difference of 1 international volt between the

- international telephone address

terminals. One international farad equals 0.99952 absolute farad. International Fixed Public Radiocommunication Sewice-A fixed service, the stations of which are open to public correspondence, intended to provide radiocommunication between the United States or its territories and foreign points. international henry-The inductance that produces an electromotive force of 1 international volt when the current is changing at a rate of 1 international ampere per second. One international henry equals 1.00018 absolute henrys. international joule-The energy required to transfer 1 international coulomb between two points having a potential difference of 1 international volt. One intemational joule equals 1.OOO18 absolute joules. International Morse code- Also called continental code. 1. A system of dot-and-dash signals used chiefly for international radio and wire telegraphy. It differs from American Morse code in certain code combinations only. 2. The Morse code that matches the English-language alphabet. international ohm-The resistance at 0°C of a column of mercury of uniform cross section 106.300 centimeters in length and with a mass of 14.4521 grams. One international ohm equals 1.00048 absolute ohms. International Radio Consultative Committee-Abbreviated CCIR. An international committee that studies technical operating and tariff questions pertaining to radio, broadcast television, and multichannel video transmissions and that issues recommendations. It reports to the International Telecommunications Union. international radio silence-Three-minute periods of radio silence, commencing 15 and 45 minutes after each hour, on a frequency of 500 lrHz only. During this time all radio stations are supposed to listen on that frequency for distress signals of ships and aircraft. international system (of electrical and magnetic units)-A system for measuring electrical and magnetic quantities by using four fundamental quantities. Resistance and current are arbitrary values that correspond approximately to the absolute o h and the absolute ampere. Length and time are arbitrarily called centimeter and second. The international system of electrical units was used between 1893 and 1947. By international agreement., it was discarded on January 1, 1948, in favor of the n+a (Giorgi)system. international telecommunication service-A telecommunication service between offices or stations in different states, or between mobile stations that are not in the same state or that are subject to regulation by Werent states. International Telecommunications Satellite Consortium -See INTELSAT. International Telecommunication Union --The United Nations specialized agency that deals with tele communications. Its purpose is to provide standardized communications procedures and practices, including frequency allocation and radio regulations on a worldwide basis. International Telegraph Consultative Committee -Abbreviated CCIT. An international committee responsible for studying technical operating and tariff questions pertaining to telegraph and facsimileand issuing recommendations. It reports to the International Telecommunications Union. international telephone address-A code not exceeding 12 digits that specifies a unique address for any telephone in the world. It consists of (a) a country or regional identity code of one, two, or three digits; (b) a three-digit numbering plan area code; (c) a two- or

International Telephone Consultative Committee three-digit central office code; plus (d) a four-digit station number.

International Telephone Consultative Committee -Abbreviated CCIF. An international committee

responsible for studying and issuing recommendations regarding technical operations and tariff questions pertaining to ordinary telephones; carrier telephones; and music, picture, television, and multichannel telegraph transmission over wire line. It reports to the International Telecommunication Union. international temperature scale -A temperature scale adopted in 1948 by international agreement. Between the boiling point of oxygen (-182.97'C) and 630.5"C it is based upon the platinum resistance thermometer. From 630.5"C to 1063.0"C it is based on the platinum rhodium thermocouple, and above 1063.0"C on the optical pyrometer. international volt-The voltage that will produce a current of 1 international ampere through a resistance of 1 international ohm. One international volt equals 1.00033 absolute volts. international watt -The power expended when 1 international ampere flows between two points having a potential difference of 1 international volt. One international watt equals 1.00018 absolute watts. Internet-A vast collection of many computer networks that span the entire world and communicate across dedicated high-speed phone lines using a single protocol family called TCP/IP. The network used for electronic mail, file transfers, chat services, and general data communications. It consists of a backbone connected via gateways to many smaller networks such as LANs and WANs, and thus each network can access every other network. Internet gateway-An online service that allows access to the Internet. Internet protocol-See IP. Internet service provider-See ISP. internetworking -The technique of connecting individual LANs to form a larger network. internode -Communication paths that originate in one node and terminate in another. interoffice trunk-The telephone channel between two central offices. interoperability--The ability of computer equipment from different manufacturers to work together compatibly. i n t e r p h a s e transformer- An autotransformer or a set of mutually coupled reactors used with three-phase rectifier transformers to modify current relationships in the rectifier system and thereby cause a greater number of rectifier tubes to carry current at any instant. i n t e r p h o n e -A telephone communication system wholly contained within an aircraft, ship, or activity. i n t e r p h o n e s y s t e m -An intercommunication system like that in an aircraft or other mobile unit. interpolate-To estimate the values of a function that are intermediate between those already known. interpolation -1. The process of finding a value of a function between two known values. Interpolation may be performed numerically or graphically. 2. The process of determining a reading falling between two adjacent gradations on an analog meter scale. interpole -A small auxiliary pole placed between the main poles of a direct-current generator or motor to reduce sparking at the commutator. interposition trunk- A trunk connecting two positions of a large switchboard so that a line on one position can be connected to a line on the other position. interpreter -1. A system program that converts and executes each instruction of a high-level language program into machine code as it runs, before going

- interrupt

390

on to the next instruction. An interpreted program is slow-as much as 20 times slower than an assembled program- but speeds up program development because the effect of source changes can be seen immediately. 2. A computer executive routine by which a stored program expressed in pseudocode is translated into machine code as a computation progresses, and the indicated operation is performed by means of subroutines as they are translated. 3. Programs that translate an assembled program into a complete machine-code listing on a line-by-line basis. If a statement is used in a program 10 times, it will be translated 10 times. 4. In a computer, a language translator that accepts high-level language (e.g., BASIC or Pascal) input text and translates this text into a special intermediate code that is simulated (interpreted) by a system program. Usually this intermediate code cannot be directly executed on a general-purpose processor. 5. A program that calls on subroutines to execute a program. Example: add two numbers, then divide by another number. BASIC is usually implemented as an interpreter. 6. A punch-card machine that will read the information conveyed by holes punched in a card and print its translation in characters arranged in specified rows and columns on the card. interpreter code -A computer code that an interpretive routine can use. interpretive programming -The writing of computer programs in a pseudo machine language, which the computer precisely converts into actual machine-language instructions before performing them. interpretive routine -Computer routine designed to transfer each pseudocode and, using function digits, to set a branch order that links the appropriate subroutine into the main program. interrecord gap -Also called interblock space. See IRG. interrogate-1. To determine the state of a device or circuit. 2. To retrieve information from computer files by use of predefined inquiries or unstructured queries handled by a high-level retrieval language. interrogation-The triggering of one or more transponders by transmitting a radio signal or combination of signals. interrogation signal-A pulsed or cw signal emitted to initiate a reply signal from a transponder or responder. interrogation suppressed time delay- The overall fixed time that elapses between transmission of an interrogation and reception of the reply to this interrogation at zero distance. interrogator- Also called challenger. A radio transmitter used to trigger a transponder. interrogator-responser- A combined radio transmitter and receiver for interrogating a transponder and displaying the replies. interrupt -1. A processor feature that allows the currently executing program to be deferred in favor of servicing another. 2. A special instruction from a computer that temporarily disrupts normal operation and changes the normal flow of instruction execution. 3. In a computer, a break in the normal flow of a system or routine such that the flow can be resumed from that point at a later time. The source of the interrupt may be internal or external. 4.A method of stopping a process and identifying that a certain condition exists. In graphic systems, interrupts can originate from data entry devices, the display list, the host computer, the refresh clock, and display error conditions. When an interrupt occurs, the host computer and display refresh cease until the interrupt is answered and processed. At that time, the host computer will restart the refresh-usually from where it was halted.

391

interrupted continuous waves

If a new display list is to be presented, the display starts at the beginning of the list. 5. To stop a process in such a way that it can be resumed. interrupted continuous waves-Abbreviated ICW. Continuous waves that are interrupted at an audiofrequency rate. interrupt enable-See interrupt mark. interrupter -1. A magnetically operated device used for rapidly and periodically opening and closing an electric circuit in doorbells and buzzers and in the primary circuit of a transformer supplied from a dc source. 2. A device used to produce interrupted ringing cycles. It also may be employed with the release alarm to start signal alarm circuits of the switching equipment and thereby provide timed delay in the sounding of a failure alarm. 3. An electrical, electronic, or mechanical device that periodically interrupts a continuous current to produce pulses. 4.A device that produces an electrical output signal when an object breaks the light (visible or invisible) between a light source and a photodetector. interrupter contacts-On a stepping relay, an additional set of contacts operated directly by the ama-

m.

interrupting capacity-The maximum power in the arc that can be interrupted by a circuit breaker or fuse without the occurrence of restrike or violent failure. Rated in volt-amperes for ac circuits and in watts for dc circuits. interrupting rating- 1. Conditions under which the contact of a relay must interrupt with a prescribed duty cycle and contact life. 2. The amount of current that a fuse can interrupt without the fuse cartridge rupturing or showing any external sign of damage. interrupting time-In a circuit breaker, the interval between the energizing of the trip coil and the interruption of the circuit, at the rated voltage. interrupt latency-The delay between an interrupt request and acknowledgment of the request. interrupt mark-A mechanism that allows a program to specify whether or not an interrupt request will be accepted by the computer (sometimes called interrupt enable). interrupt request-A signal to a computer that temporarily suspends the normal sequence of a routine and transfers control to a special routine. Operation can be resumed from this point later. Ability to handle interrupts is very useful in communication applications, where it allows the microprocessor to service many channels. interrupt vector- 1. Typically, two memory locations assigned to an intempting device and containing the starting address and processor status word for its service routine. 2. A function that facilitates fast handliig of external interrupts by having the hardware supply a value corresponding to the device causing the interrupt. This value then becomes an index into the interrupt vector that contains a pointer to the appropriate interrupt service routine. interstage-Between stages. interstage coupling -Coupling between stages. interstage transformer-A transformer that couples two stages together. interstation noise suppression -Canceling of the noise that occurs when a high-gain radio receiver with automatic volume control is tuned between stations. interstitial site-A position that is inside a crystal lattice but is not one of the proper sites ordinarily occupied by the atoms of the crystallinematerial. Impurity ions of the proper size can occupy such positions in a lattice that is otherwise regular. intersymbol interference -1. In a transmission system, extraneous signal energy during one or more

- intrinsic conduction

keying intervals that tends to hinder the reception of the signal in another keying interval. 2. The disturbance that results from this condition. interties-See interconnection, 1. intertoll tnrnk-A trunk linking toll offices in different telephone exchanges. interval-A period from one event to another. An interval timer controls the time a load is energized or deenergized. interval calibration -See step calibration. interval circuit-A circuit that is energized during timing only. This can be accomplished by using a timer with interval contacts, or by using a timer with delayed contacts in series with the start switch, or one with instantaneous contacts in series with delayed contacts. interval contacts-In a timer, contacts that are actuated only for the duration of the preset time interval. interval tinier- 1. A device for measuring the time interval between two actions. 2. A timer that switches electrical circuits on or off for the duration of the preset time interval. 3. A hardware or software clock that generates an interrupt after a specified period has elapsed. interword space-In telegraphy, the space between words or coded p u p s . It is equal to seven unit lengths. intonation-The slight modification of pitch, or frequency, that makes a note sound flat or sharp compared with the natural frequency of the note played. intracardiac-Pertaining to instruments whose pickup element is inserted through a vein directly into the heart chambers. intraconnections (microelectronics) -1. Those conductors and connections that are in continuous integral contact with the substrate or circuit elements of an integrated circuit. 2. See interconnection. intraoffice trunk-Telephone channel used to interconnect two customer lines within the same central office. intrinsically safe -Incapable of releasing sufficient electrical energy to ignite a specific atmospheric mixture under normal conditions or such abnormal conditions as accidental damage to any part of the equipment or wiring insulation, failure of electrical components, application of overvoltage, or improper adjustment or maintenance operations. intrinsic-barrier diode-A pin diode in which a thin region of intrinsic material separates the n-type and p-type regions. intrinsic-barrier transistor-A pnip or npin transistor in which a thin region of intrinsic material separates the collector from the base. intrinsic brightness-The luminous intensity measured in a given direction per unit of apparent (projected) area when viewed from that direction. intrinsic characteristics-Characteristics of a material that depend on the material itself and do not result from impurities. intrinsic coercive force--The magnetizing force that, when applied to a magnetic material in a direction opposite to that of the residual induction, reduces the intrinsic induction to zero. intrinsic coercivity-The measurement (in oersteds) of the force required to reduce the intrinsic induction of the magnetized material to zero. intrinsic concentration -In a semiconductor, the number of minority carriers that exceeds the normal equilibrium number. intrinsic conduction -In an intrinsic semiconductor, the conduction associated with the directed movement of electron-hole pairs under the influence of an electric field.

intrinsic contact potential difference

- inverse Fourier transform

intrinsic contact potential difference-The true potential difference between two spotlessly clean metals in contact. intrinsic delay-See insertion delay. intrinsic detector -A photodetector composed of a photoconductive material that, when exposed to radiation, conducts without the aid of added impurities and does not have to be cooled to the level of extrinsic material. Examples of intrinsic materials are silicon and cadmium sulfide. intrinsic electric s t r e n g t h -The characteristic electric strength of a material. intrinsic flux-The product of the intrinsic flux density and the cross-sectional area of a uniformly magnetized sample of material. intrinsic flux density-In a sample of magnetic material, the excess of the normal flux density over the flux density in a vacuum for a given magnetizing field strength. In the cgs system, the intrinsic flux density is numerically equal to the difference between the ordinary flux density and the magnetizing field strength. intrinsic hysteresis loop-A curve that shows intrinsic flux density as a function of magnetizing field strength, where the magnetizing field is cycled between equal values of opposite polarity. Hysteresis is indicated by the fact that the ascending and descending portions of the curve do not coincide. intrinsic induction -The excess magnetic induction produced in a magnetic material by a given magnetizing force, over the induction that would be produced by the same magnetizing force in a vacuum. intrinsic insulation -Any method of isolating fields or current within a semiconductor or other substrate. Among these are thermal oxidation, fabrication of an isolating layer of intrinsic semiconductor material, and creation of one or more back-based functions. intrinsic- junction transistor -See intrinsic-region transistor. intrinsic layering- The method of separating two regions of conductive semiconductor by a region of nearintrinsic semiconductor material. This material differs enough in resistivity from the adjacent regions to serve as an insulator. intrinsic material -A semiconductor material in which there are equal numbers of holes and electrons, i.e., no impurities. intrinsic mobility-The mobility of electrons in an intrinsic semiconductor or in a semiconductor having a very low concentration of impurities. intrinsic noise-Noise that is due to the device or transmission path and is independent of modulation. intrinsic permeability-Ratio of intrinsic normal induction to the corresponding magnetizing forces. intrinsic photoconductivity-The absorption of a photon raising an electron across the forbidden gap from valence to conduction band of the semiconductor, whereby conductivity is increased and incident radiation may be measured. intrinsic photoemission -The photoemission that would occur if a crystal were pure and its structure perfect. intrinsic properties -The semiconductor properties that are characteristic of the pure, ideal crystal. intrinsic Q-See unloaded Q (switching tubes). intrinsic region -See i region; depletion region. intrinsic-region transistor- Also called intrinsicjunction transistor. A four-layer transistor with an intrinsic region between the base and collector. Examples are npin, pnip. npip, and pnin transistors. intrinsic reliability-The probability that a device will perform its specified function, determined by

392

statistical analysis of the failure rates and other characteristics of the parts and components the device comprises. intrinsic semiconductor- 1. A semiconductor in which some hole and electron pairs are created by thermal energy at room temperature, even though there are no impurities in it. 2. A semiconductor with substantially the same electrical properties as those of the ideal crystal. 3. An element or compound that has the same electron energy band configuration as an insulator, but has a forbidden energy gap that is sufficiently narrow to permit transfer of electrons from the valence band to the conduction bands at normal temperatures. Conduction in an intrinsic semiconductor takes place via equal number of conduction band electrons and valence band holes. intrinsic standoff ratio-In a unijunction transistor, the difference between the emitter voltage at the peak point with a specific interbase voltage and the forward voltage drop of the emitter junction, divided by the voltage on base 2 with respect to base 1. intrinsic temperature range -The temperature range at which impurities or imperfections within the crystal do not modify the electrical properties of a semiconductor. intrusion alarm system-An alarm system for signaling the entry or attempted entry of a person or an object into the area or volume protected by the system. Invar-An alloy containing 63.8 percent iron, 36 percent nickel, and 0.2 percent carbon. Has a very low thermal coefficient of expansion. Used primarily as resistance wire in wirewound resistors. inverse beta -The transistor gain that results when the emitter and collector loads are physically reversed in the operation of a circuit. inverse common base -Transistor circuit configuration in which the base terminal is common to the input circuit and to the output circuit and in which the input terminal is the collector terminal and the output terminal is the emitter terminal. inverse common collector-Transistor circuit configuration in which the collector terminal is common to the input circuit and to the output circuit and in which the input terminal is the emitter terminal and the output terminal is the base terminal. inverse common emitter-Transistor circuit configuration in which the emitter terminal is common to the input circuit and to the output circuit and in which the input terminal is the collector terminal and the output terminal is the base terminal. inverse direction of operation-A mode of operating a transistor in which the nominal collector region acts as an emitter and in which the net flow of minority carriers is from the nominal collector region to the base region. inverse electrical characteristics-In a transistor, those characteristics obtained when the collector and emitter terminals are interchanged and the transistor is then tested in the normal manner. inverse electrode current -The current flowing through an electrode in the opposite direction from that for which the tube was designed. inverse feedback-See negative feedback. inverse-feedback filter-A tuned circuit at the output of a highly selective amplifier having negative feedback. The feedback output is zero for the resonant frequency, but increases rapidly as the frequency deviates. inverse Fourier transform -A mathematical operation that synthesizes a time-domain signal from its complex spectrum components. If a time-domain signal is Fourier transformed and then inverse Fourier transformed, the original time function is reconstructed.

393 inverse limiter-A transducer with a constant output for inputs of instantaneous values within a specified range. Above and below that range, the output is linear or some other prescribed function of the input. inverse networks--Any two two-terminal networks in which the product of their impedances is independent of frequency within the range of interest. inverse neutral telegraph transmission -A form of transmission in which zero-current intervals are used as marking signals, and current pulses of either polarity are used as spacing signals. inverse-parallel connection -See back-to-back circuit. inverse peak voltage-The peak instantaneous voltage across a rectifier tube during the nonconducting half-cycle. inverse photoelectric effect -The transformation of the kinetic energy of a moving electron into radiant energy, as in the production of X-rays. inverse piezoelectric effect-Contraction or expansion of a piezoelectric crystal under the influence of an electric field. inverse ratio--The seesaw effect whereby one value increases as the other decreases or vice versa. inverse-square law -. 1. The strength of a field, or the intensity of radiation, decreases in proportion to the square of the distance from its source. 2. The law stating that the illuminance (or irradiance) from a point source varies as the inverse square of the distance between the source and the receiver. inverse time-A qualifying term applied to a relay, indicating that its time of operation decreases as the magnitude of the operating quantity increases. inverse voltage-The effective voltage across a rectifier tube during the half-cycle when current does not flow. inverse Wiedemann effect -See Wiedemann effect. inversion -1. The bending of a radio wave because the upper part of the beam is slowed down as it travels through denser air. This may occur when a body of cold air moves in under a moisture-laden body of air. 2. The producing of inverted or scrambled speech by beating an audio-frequency signal with a fixed band of the resultant beat frequencies. The original low audio frequencies then become high frequencies and vice versa. inversion layer-A layer of doped semiconductor material that has changed to the opposite type, such as a p layer at the surface of an n-doped region. Surface inversion layers may be the result of surface ions or dopant gettering by surface passivation material or the action of induced electric fields. See also channel, 6. inverted amplifier-An amplifier stage containing two vacuum mbes. The control grids are grounded, and the driving excitation is applied between the cathodes. The grids then serve as a shield between the input and output circuits. Thus, the output-circuit capacitance is greatly reduced. inverted-L antenna- An antenna consisting of one or more horizontal wires with a vertical wire connected at one end. inverted s p e e c h -See scrambled speech. inverter- 1. A circuit that takes in a positive signal and puts out a negative one, or vice versa. 2. A device that changes alternating current to direct current or vice versa. It frequently is used to change 6-volt or 12-volt direct current to 110-volt alternating current. 3. A device that accepts an input that is a function of the maximum voltage and changes it into an output that is a function of both the maximum voltage and time. 4. A circuit with one input and one output, and whose function is to invert the

inverse limiter - I/O device

Inverte&L antenna. input. When the input is high, the output is low, and vice versa. The inverter is sometimes called a NOT circuit, since it produces the reverse of the input. 5. A device or circuit that complements a Boolean function.

Inverter, 4.

inverter circuff-See NOT circuit. inverting arnpliiier-An amplifier in which the output p o l a r i ~is the opposite of the input polarity. Such an amplifier obtains negative feedback through a connection from the output to the input, and with high gain it is widely used as an operational amplifier. inverting connection -The closed-loop connection of an operational amplifier when the forward gain is negative for dc signals. A 180" phase shift. inverting input-An input terminal of a differential amplifier that produces an output signal of opposite phase (shifted 180") than that of the input signal. inverting parametric device-A parametric device whose operation depends essentially upon three frequencies: a harmonic of the pump frequency, and two signal frequencies, of which the higher signal frequency is the difference between the pump harmonic and the lower signal frequency. invisible file-See hidden file. invister -A high-frequency, high-transconductance unipolar structure made by means of lateral diffusion. inward-outward dialing system-A dialing system by means of which calls within the local exchange area may be dialed directly to or from base private branch exchange telephone stations without the assistance of an operator at the base private branch exchange. inward WATS-Inward wide area telephone service that permits a customer, for a monthly charge, to receive incoming station-to-station calls from telephones within prescribed service areas or in six interstate bands, without charge to the calling party. A telephone service similar to WATS but applicable to incoming calls only. 1/0 or i/o-Abbreviation for inputloutput. 1. The components of a computer system's architecture that control the Bow of data and instructions to and from the CPU. 2. Any equipment that introduces data into or extracts data from a data communications system. IOC-See integated optical circuit. I/O device -Abbreviation for inputloutput device. 1. A disk drive, magnetic tape unit, printer, or similar

I/O electrical isolation

- ionization gage

device that transmits data to or receives data from a computer or secondary storage device. 2. A general term for equipment used to communicate with a computer. 3. A device that supplies data and instructions to the computer and receives the computer’s output, or a circuit that interfaces with such a device. 4. InpuUoutput equipment used to communicate with a system. I/O electrical isolation-Separation of the field wiring circuits from the logic level circuits of the PC, typically done with optical isolation. I/O modules -General-purpose circuit modules that interface a microprocessor to relays, switches, and transducers. Each module contains almost all necessary interface circuitry in one package either to sense a load, control a switch, or condition a transducer signal so that practically no other interface design is required. ion - 1. An atom that has become charged by gaining or losing one or more orbiting electrons. A completely ionized atom is stripped of all electrons. 2. An atom or molecule with an electrostatic charge. 3. The charged particle formed when one or more electrons are taken from or added to a previously neutral atom or molecule. An atom that has gained additional electrons is thus a negative ion, whereas an atom that has lost an electron or electrons is a positive ion. ion charging -In a storage tube, spurious charging or discharging caused by ions striking the storage surface. ion counter -A tubular chamber for measuring the ionization of air. ion-exchange electrolyte cell-A fuel cell that uses the reaction of hydrogen with oxygen from the air. It is similar to the standard hydrogen-oxygen fuel cell, except that an ion-exchange membrane replaces the liquid electrolyte. Operation is at atmospheric pressure and room temperature. ionic conductivity-The transit phenomenon that occurs as a result of positive and/or negative charge movement in an electrolyte when placed in an electric field. ionic focusing-Focusing the electron beam in a cathode-ray tube by varying the filament voltage and temperature to change the electrostatic focusing field automatically produced by the accumulation of positive ions in the tube. ionic-heated cathode-A cathode that is heated primarily by bombardment with ions. ionic-heated c a t h o d e tube- An electron tube containing an ionic-heated cathode. ionic tweeter-A type of speaker in which a varying electrostatic field activates a mass of air ionized by a highvoltage radio-frequency field. Ionic speakers are capable of extremely extended high-frequency response (up to 100 kHz or so) because of the extreme lightness of the ionic “diaphragm.” ion implantation- 1. A precise and reproducible method of semiconductor doping in which selected dopants are ionized and accelerated at high velocity to penetrate the semiconductor substrate and become deposited below the surface. Charged atoms (ions) of elements such as boron, phosphorus, or arsenic are accelerated by an electric field into the semiconductor material. This technique ensures uniform, accurately controlled depth of implantation and ionic diffusion in the water. 2. A processing step by which standard p-channel diffused MOS devices are made directly compatible with lTL/DTL logic. It is a highly controllable process that allows the adjusting of gate threshold voltages and also allows the fabrication of both enhancement-mode and depletion-mode transistors on the same chip. 3. A process that uses accelerated atoms to implant source and drain regions in metal-oxide semiconductors. It offers higher

394 speed and lower threshold voltages and can also be used with PMOS, NMOS, and CMOS.

Ion implantation.

ion-implanted MOS- Abbreviated IMOS. A method for doping substrates with a stream of ionized dopant atoms. Ions are electrically shot into the substrate instead of diffusing atoms at high temperatures. ionization- 1. The dissociation of inert-gas atoms into positive and negative ions in an electric field, resulting in the emission of light. 2. The state of an insulator in which it facilitates the passage of current because of the presence of charged particles (usually induced artificially). 3. The electrically charged particles produced by highenergy radiation (such as light or ultraviolet rays) or by the collision of particles during thermal agitation. formation of ions. The process of giving a net ch geThe to a neutral atom or molecule by adding or subtracting an electron. This can be accomplished by radiation or by a strong electric field. ionization arcover- 1. Formation of an electrical arc between terminals or contacts as a result of ionization of the adjacent air or gas. 2. Formation of an arc between the terminals of a satellite antenna as the satellite passes through the ionized regions of the ionosphere. ionization c h a m b e r - 1. An enclosure containing two or more electrodes between which an electric current may pass when the gas within is ionized. The current is a measure of the total number of ions produced in the gas by externally induced radiations. 2. A chamber containing a gas through which ionizing particles pass. A voltage is applied across the chamber so as to collect the ions produced and permit the ion current to be measured. ionization current -The current resulting from the movement of electric charges, under the influence of an applied electric field, in an ionized medium. ionization e n e r g y -Sometimes called ionization potential. The minimum amount of energy (usually expressed in electronvolts) required to eject an electron from a molecule. ionization f a c t o r -The difference between percent power factors of a dielectric at two specified values of electrical stress. The lower of the two stresses is usually selected so that the effect of ionization on power factor at this stress is negligible. ionization gage-1. A gage that measures the degree of a vacuum in an electron tube by the amount of ionization current in the tube. 2. A type of radiation detector that depends on the ionization produced in a gas by the passage of a charged particle through it. One

8

395

ionization-gagetube

of the best known is the Geiger-Mueller counter. Cloud chambers and spark chambers can also be included in this category. ionization-gage tube- An electron tube that meamres low gas pressure by the amount of ionization current produced. ionization potential- 1. The energy, expressed in electronvoits, needed to remove one electron from a neutral atom or molecule in its ground state. 2. The amount of energy, for a particular kind of atom, required to remove an electron from the atom to infinite distance. The ionization potential is usually expressed in volts. ionization pressure--- An increase in the pressure in a gaseous discharge tube due to ionization of the gas. ionization resistance-See corona resistance. ionization smoke detector -A smoke detector in which a small amount of radioactive material ionizes the air in the sensing chamber, thus rendering it conductive and permitting a current through the air between two charged electrodes. This effectively gives the sensing chamber an electrical conductance. When smoke particles enter the ionization area, they decrease the conductance of the air by attaching themselves to the ions, causing a reduction in mobility. When the conductance is less then a predetermined level. the detector circuit responds. ionization time- 1. The time interval between the .initiation and the establishment of conduction in a gas ;tube at some stated voltage drop for the tube. 2. The elapsed time to achieve normal glow after a voltage ,greater than the breakdown voltage is applied to a glow lanap. ionization transducer- A transducer in which displacement of the force-summing member is sensed by the induced changes in differential ion conductivity.

CAPACITOR PLA SHOWN TWICE F

Ionization transducer.

ionization vacuum gage-A gage in which the operation depends on the positive ions produced in a gas by electrons as they accelerate between a hot cathode and another electrode in a vacuum. It ordinarily covers a mm of mercury. pressure range of 1 0 - ~ to ionizationvoltage (corona level) -The minimum value of falling rms voltage that sustains electrical discharge within the vacuous or gas-filled spaces in the cable construction or insulation. ionize-To free an electron from an atom or molecule (e.g., by X-ray bombardment) and thus transform the atom

- ion spot

or molecule into a positive ion. The freed electron attaches itself to another atom or molecule, which then becomes a negative ion. ionized layers-Layers of increased ionization within the ionosphere. They are responsible for absorption and reflection of radio waves and are important for communication and for tracking satellites and other space vehicles. ionizing event-Any interaction by which one or more ions are produced. ionizing radiation-1. Radiant electromagnetic energy and high-energy particles that cause the division of a substance into parts carrying positive and negative charges. High-energy particles can directly ionize substances, whereas electromagnetic radiation sets in motion charged particles that then produce ions. 2. Generally, any radiation having sufficient energy to dislodge electrons from atoms or molecules while traveling through a substance, thereby producing ions. ion migration-1. Movement of the ions produced in an electrolyte by application of an electric potential between electrodes. 2. The movement of free ions within a material or across the boundary between two materials under the influence of an applied electric field. ionophone-A high-frequency speaker in which the audio-frequency signal modulates an rf supply to maintain an arc in the mouth of a quartz mbe. The resultant modulated wave acts directly on the ionized air under pressure and thus creates sound waves. ionosphere-The part o f the earth’s outer atmosphere where sufficient ions and electrons are present to affect the propagation of radio waves. ionospheric absorption-The loss of energy of a radio wave as it travels through the atmosphere, setting particles in motion. The energy needed to create this motion is equal to the loss. ionospheric disturbance- 1. The variation in the state of ionization of the ionosphere beyond the normal observed random day-to-day variation from the average value for the location, date, and time of day under consideration. 2. Change in the part of the earth‘s outer atmosphere (ionosphere) that affects transmission and reception of radio signals. ionospheric D scatter meteor burst-A phenomenon in which the penetration of meteors through the D region of the ionosphere affects ionospheric scatter communications. ionospheric error-Also called sky enor. In navigation, the total systematic and random error resulting from reception of the navigational signal after it has been reflected from the ionosphere. It may be due to variations in the transmission path, uneven height of the ionosphere, or uneven propagation within the ionosphere. ionospheric prediction-The forecasting of ionospheric conditions and the preparation of radio propagation data derived from it. ionospheric scatter -See forward scatter. ionospheric storm -An ionospheric disturbance associated with abnormal solar activity and characterized by wide variations from normal, including turbulence in the F region and increases in absorption. Often the ionization density is decreased and the virtual height is increased. The effects are most marked in high magnetic latitudes. ionospheric wave-Also called a sky wave. A radio wave that is propagated by way of the ionosphere. ion sheath-A positive-ion film that forms on or near the grid of a gas tube and limits its control action. ion spot -1. In camera or image tubes, the spurious signal resulting from bombardment of the target or photocathode by ions. 2. On a cathode-ray-tube screen,

ion trap - iron-vane instrument an area where the luminescence has been deteriorated by prolonged bombardment with negative ions. 3. A spot on the fluorescent surface of a cathode-ray tube that is somewhat darker than the surrounding area because of bombardment by negative ions, which reduce the sensitivity. ion trap- Also called a beam bender. 1. An electrongun structure and magnetic field that diverts negative ions to prevent their burning a spot in the screen, but permits electrons to flow toward the screen. 2. An arrangement of magnetic fields and apertures that will allow an electron beam to pass through but will obstruct the passage of ions.

Ion trap.

I/O rack-A chassis that contains YO modules. I/O scan -The time required for the PC processor to monitor all inputs and control all outputs. The YO scan repeats continuously. IP -Abbreviation for Internet Protocol. The Internet standard protocol that provides a common layer over dissimilar networks, used to move packets among host computers and through gateways if necessary. ,/ -Symbol for the plate current of a vacuum tube. I-phase carrier- Also called in-phase carrier. A carrier separated in phase by 57" from the color subcarrier. ips- Abbreviation for inches per second. Used for specifying the speed of a tape traveling past the heads of a tape recorder. The most common speeds are 17/8 ips (4.75 cmls); 33/4 ips (9.5 c d s ) and 71/2 ips (19 cmls). IR- 1. Abbreviation for interrogator response. 2. Abbreviation for infrared. 3. Abbreviation for insulation resistance. That resistance offered by an insulation to an impressed dc voltage, tending to produce a leakage current through the insulation. PR-Power in watts expressed in terms of the current ( I ) and resistance (R). IRAC -Acronym for Interdepartmental Radio Advisory Committee. It is composed of representatives of eleven government agencies: The FCC; Army; Navy; Air Force; Maritime Commission; and the Treasury, State, Commerce, Agriculture, Interior, and Justice Departments. IR compensation-A control device that compensates for voltage drop due to current flow. /R drop - 1. The voltage produced across a resistance (R)when there is a current ( I ) through the resistor. 2. The voltage drop that exists across a resistance when a current is flowing through it.

396

IRE -Abbreviation for Institute of Radio Engineers, an organization now merged with AIEE. See IEEE. IRED-An infrared-emitting diode that emits photons in the infrared spectrum when forward biased. See also light-emitting diode. i region- Abbreviation for intrinsic region. In silicon, a pure region of the group rV element (Le., having neither excess holes or excess electrons, and therefore having very high resistivity). IRG -Abbreviation for interrecord gap. 1. Erased area between records that allows stop/start and speed standardization when writing or reading data blocks on magnetic tape. 2. The space between records on magnetic tape caused by delays involved in starting and stopping the tape motion. This gap is used to signal that the end of a record has been reached. iridescence-The rainbow exhibition of colors in a body, usually caused by interference of light of different wavelengths reflected from superficial layers in the surface of a material. iris-Also called diaphragm. 1. In a waveguide, a conducting plate (or plates) that is very thin (compared with the wavelength) and occupies part of the cross section of a waveguide. When only a single mode can be supported in the waveguide, an iris appears substantially as a shunt admittance. 2. An adjustable aperture built into a camera lens to permit control of the amount of light passing through the lens. iris d i a p h r a g m -A simple mechanism used to vary the diameter of an aperture. Consists of a number of thin, arc-shaped, metal blades that surround the aperture, each blade having a lower stud at one end and an upper stud at the other end. The lower studs fall into holes in a fixed ring surrounding the aperture, while the upper studs are held by radial slots in a rotatable control ring. Iris openings are measured in f-stops. PR loss- The power lost in transformers, generators, connecting wires, and other parts of a circuit because of the current I through the resistance R of the conductors. iron constantan -A combination of metals used in thermocouples, thermocouple wires, and thermocouple lead wires. Constantan is an alloy of copper, nickel, manganese, and iron. The iron wire is the positive, the constantan the negative wire. iron-core coil-A coil in which iron forms part or all of the magnetic circuit, linking its winding. In a choke coil, the core is usually built up of laminations of sheet iron. iron-core transformer -A transformer in which iron forms part or all of the magnetic circuit, linking the transformer windings. ironless rotor motor-A motor that has a stationary permanent magnet located in the center of the rotor. The housing is made of soft steel and provides a return path for magnetic flux. Rotor coils are wound on a nonmagnetic cage. The rotating member consists only of the hollow cage, the winding shaft, and commutator. Advantages include the elimination of cogging, lower starting voltages, and smoother starting and running. The motors are lightweight, hence inertia is low, providing a high torque-to-inertia ratio and high acceleration. The main disadvantage is that the complex construction is more expensive. iron Ioss-See core loss. iron-vane instrument- An indicating instrument whose operating portion consists of two iron bars, one fixed, one pivoted, placed parallel to each other inside a signal coil. Current through the coil magnetizes the bars in the same direction, and they repel each other, causing the pointer to pivot against the force of a hairspring. A damping vane may be used to slow the movement of the

397

-

pointer. Deflection is the same for ac or dc; the meter does not have polarity. The instrument has a nonlinear scale, and readings below 1/5 scale are extremely difficult to make. Because of inductance effects, use of this type of meter is limited to power-he frequencies.

POINTER

VANE

\?ALUMINUM

MOVING IRON VANE

Iron-vane instrument.

irradiance -The incident radiated power per unit area of a surface; the radiometric counterpart of illumination, usually expressed in watts per square centimeter. irradiation -1. The application of X-rays, radium rays, or other radiation. 2. The amount of radiant energy per unit area received during a given time interval. This term is used in radiological therapy as well as in describing accidental exposure to radiation. It also can be used to denote radiant energy that ultimately passes through the skin to supply power to implanted electronic devices. 3. The exposure of a material to highenergy emissions. In insulations, done for the purpose of favorably altering the molecular structure. irregui!arity-A change from normal. E A - Abbreviation for Industry Standard Architeciture. The original bus architecture developed by IBM for its AT computer and opened up for use by other manufacturers. 8-scan-A rad= display in which a target appears .BS a complete circle when the radar antenna is correctly pointed at it. the radius of the circle being proportional to the target distance. I-scope-See I-scan. ISDN.- Abbreviation for integrated services digital network. 1. A digital telephone service network that allows transmission of data, voice, and images over one phone line simultaneously. It can provide speeds of roughly 128,000 bits per second over regular phone lines. In practice, most users are limited to 56,000 or 64,000 bits per second. 2. Telephone technology that provides digital access to voice and data network services for sending speech, data, and video across one line simultaneously. iSHM-The International Society of Hybrid Microelectronics. I signal -Also called the fine-chrominance primary. 1. A signal formed by the combination of +.74 of an R - Y signal and -0.27 of a B - Y signal. One of the two signals used to modulate the chrominance subcarrier, the other being the Q signal. 2. Also known as the in-phase signal. The color sidebands produced by modulating the color subcarrier at a phase 57” removed from the burst reference phase. This signal is capable of reproducing the range of colors from orange to cyan (bluish-green).

irradiance - isolation amplifier ISM equipment -A Federal Communications Commission designation for industrial, scientific, and medical equipment. isobar -1. On meteorological maps, a line denoting places having the same atmospheric pressure at a given time. 2. One of a group of atoms or elements having the same atomic weights but different atomic numbers. isochromatic-Having the same calor, as with the lines of the same tint in the interference figure of anisotropic crystals. isochrone-On a map or chart, a line joining points associated with a constant time difference in the reception of radio signals. i s o c h r o n e determination -A radio location in which a position line is determined by the difference in transit times of signals along two paths. isochronous- 1. Equal in length of time. 2. Occurring at equal intervals of time. 3. Describes modems, terminals, and transmissions in which all bits are of equal duration. There are no start or stop bits as in asynchronous transmissions, and no clocking signals as in synchronous transmissions. i s o c h r o n o u s circuits-Circuits having the same resonant frequency. isochronous distortion -A measure of a modem’s dynamic operation. i s o c h r o n o u s multiplexer -A multiplexer that can interleave two time-independent data streams into one higher-speed stream independent of the master timing control required by a synchronous multiplexer. isoclinic line-See aclinic line. isodynamic lines -On a magnetic map, lines passing through points of equal strength of the earth’s magnetic field. isoelectric-Uniformly electric throughout or having the same electric potential, and therefore producing no current. isoelectronic-Pertaining to atoms having the same number of electrons outside the nucleus of the atom. isolated -Utterly cut off; refers to that condition in which a conductor, circuit, or device is not only insulated from another (or others), but the two are mutually unable to engender current, emf, or magnetic flux in each other. As commonly used, insulation is associated predominantly with direct current, whereas isolation implies additionally a bulwark against ac fields. isolated amplifier -A differential amplifier in which the input-signal lines are conductively isolated from the output-signal lines and chassis ground. isolated I/O module -A module that has each input or output electrically isolated from every other input or output on that module, i.e., each input or output has a separate return wire. isolating diode-A diode that passes signals in one direction through a circuit but blocks signals and voltages in the opposite direction. isolating switch -A switch intended for isolating an electric circuit from the source of power. It has no interrupting rating and is intended to be operated only after the circuit has been opened by some other means. isolation-1. Electrical or acoustical separation between two locations. 2. The technique for producing a high electrical resistance between an integrated-circuit component and the substrate in which it is formed. 3. A reduction in the ability of a system to respond to an excitation or to generate an excitation. 4. A method for implementing electrical independence of devices integrated on the same integrated circuit. isolation amplifier -Also called buffer amplifier. 1. An amplifier that is used to minimize the interaction

isolation barrier

- item

bctween the circuitry which precedes and that which follows. 2. An amplifier designed to have a galvanic discontinuity between its input and output pins. This discontinuity (called an isolation barrier) must have high breakdown voltage, low dc leakage (high barrier resistance). and low ac leakage (low barrier capacitance). Three-port isolation amplifiers have an additional isolation barrier between the power-supply connection and the signal connections that allows the user to connect power in common with either the amplifier's input or its output. Isolation amplifiers generally serve the following functions not achievable with operational or instrumentation amps: sensing small signals in the presence of very high (10 volts) or unknown common-mode voltages, protecting patients undergoing medical monitoring or diagnostic measurements, and completely breaking ground loops. The isolation amplifier, as well as offering isolation, increases accuracy because of its floating input. In contrast to the instrumentation amplifier, it not only eliminates ground loop errors but further reduces the total system error, because its isolation-mode rejection ratio is generally one or two orders of magnitude higher than the common-mode rejection of an instrumentation amplifier. 3. An amplifier with input circuitry and output circuitry designed to eliminate the effects of changes made at either on the other. 4.An amplificr that has an input circuit that is galvanically (no ohmic connection) isolated from the output stage and the power-supply terminals. This isolation is provided by magnetic, optical, or mechanical coupling techniques. Isolation amplifiers are used in applications that require accurate and safe measurement of dc and low-frequency signals. 5. A circuit that amplifies a signal without needing a galvanic path between its input and output terminal. The circuit can be used to protect individuals and equipment from high voltages and to break ground loops in mcasurement systems. The high resistance and low capacitance of the isolation region permit little current leakage across its barrier and it withstands a specified high voltage without breakdowns or arcs. isolation barrier-See isolation amplifier. isolation diffusion - 1. A technique for separation of the individual components within a monolithic silicon n structure; p diffused isolation zones are used to form pn junctions that act as reverse-biased diodes. The transistors are double diffused; that is, they are processed by two diffusion steps after the isolation diffusion. 2. In monolithic integrated circuit technology, the diffusion step that generatcs back-to-back junctions to isolate active devices from one another. isolation network-A network inserted into a circuit or transmission line to prevent interaction between circuits on each side of the insertion point. isolation transformer-A transformer designed to provide magnetic coupling (flux coupling) between one or more pairs of isolated circuits, without introducing significant coupling of any other kind between them--.e., without introducing either significant conductive (ohmic) or significant electrostatic (capacitive) coupling. isolator- 1. A device that permits microwave energy to pass in one direction while providing high isolation to reflected energy in the reverse direction. Used primarily at the input of communications-band microwave amplifiers to provide good reverse isolation and minimize VSWR. Consists of microwave circulator with one port (port 3) terminated in the characteristic impedance. 2. A device that acts as a one-way valve for microwave signals to prevent stray rcceiver signals from leaking out past the LNA onto the antenna. 3. A device that allows the transmission of signals in one dircction while blocking or attenuating them in the other.

398 isolator ferrite -A microwave device that allows rf energy to pass through in one direction with very little loss but that absorbs rf power in the other direction. isolith -An integrated circuit of components formed on a single silicon slice, but with the various components interconnected by beam leads and with circuit parts isolated by removal of the silicon between them. isomer-One of two or more substances composed of molecules having the same kinds of atoms in the same proportions but arranged differently. Hence, the physical and chemical properties are different. isoplanar -A bipolar fabrication process that replaces conventional planar p+ isolation diffusion with an insulating oxide to provide isolation between active elements of a silicon integrated circuit. Circuit elements can be fabricated in less space than conventional isolation techniques with improved speed and power performance. isopulse system -In adaptive communications, a pulse coding system in which special inserted pulses indicate the number of information pulses that are transmitted. isostatic-Being subjected to equal prcssurc from every side. isothermal region -The stratosphere considered as a region of uniform temperature. isotones-A group of atoms whose nuclei have the same number of neutrons. isotope-A species of matter whose atoms contain the same number of protons as some other species, but a different number of neutrons. The atomic numbers of isotopes are identical, but the mass numbers (atomic weights) differ. See radioisotope. isotropic-1. Having properties with the same values along axes in all directions. 2. Term applied to substances having certain properties that are manifest in every direction, e.g., electrical conductivity in metals. 3. The ability to react the same regardless of direction of measurement. Isotropic materials will react consistently even if stress is applied in different directions. Stresslstrength ratio is uniform throughout material. isotropic antenna -Also called unipole. A hypothetical antenna radiating or receiving equally in all directions. A pulsating sphcre is a unipole for sound waves. In the case of electromagnetic waves, unipoles do not exist physically, but represent convenient reference antennas for expressing directive properties of actual antennas. isotropic gain of an antenna -See absolute gain of an antenna. isotropic magnet-A magnetic material having no preferred axis of magnetic characteristics. isotropic material- 1. A material having the same magnetic characteristics along any axis. 2. A substance whose properties are similar when tested in any direction. isotropic radiator-A radiator that sends out equal amounts of energy in all directions. ISP -Abbreviation for Internet service provider. A general term for any company that provides a connection to the Internet for individuals or businesses. Isv- Abbreviation for instantaneous speed variations. Short-term speed changes resulting from nonuniform capstan speed, tension changes caused by start/stop accelerations, and longitudinal vibrations that are caused by a magnetic tape's sliding over the heads and tape guides. ITDM -Abbreviation for intelligent time-division multiplexer. Also called a statistical multiplexcr. A multiplexer that assigns time slots on demand rather than on a fixed subchannel-scanning basis. item- 1. A general term denoting one of a number of similar units, assemblies. objects, etc. 2. Any unique manufactured or purchased part or assembly. that is. end product, assembly, subassembly, component, or raw material.

399 iterations per second -The number of approximations per second in iterative division in a computer; the number of times a cycle of operation can be repeated in one second. iteraticre- I. Recurring an infinite number of times. 2. Characteristic of a network with an infinite number of identical sections, or of the impedance looking into such a network iterathre array-In a computer, a large number of identical, interconnected processing modules used, with appropriate driver and control circuits, to perform simultaneous parallel operations. iterative division-In computers, a method of perhrming division by use of addition, subtraction, and mulbplication operations. A quotient of specified precision is cibtained by a series of progressively closer approximations. iterative filter-A four-terminal filter that provides iterative impedance. iterative impedance- 1. An impedance that, when connected to one pair of terminals of a four-terminal transducer, causes the same value of impedance to appear hetween the other two terminals. The iterative impedance of a uniform transmission line is equal to the characteristic impedancle of the line. In a symmetrical four-terminal

iterations per second

- IWW

transducer, the iterative impedances for the two pairs of terminals are equal and the same as the image impedances and the characteristic impedance. 2. The impedance that will terminate the output of a line or network such that the impedance then measured at the input of the line or network will be equal to the (iterative) terminating impedance. iterative process-The caiculating of a desired result by means of a repeating cycle of operations that comes closer and closer to the desired result. iterative routine-A computer routine composed of repetitive computations, so that the output of every step becomes the input of the succeeding step. ITU -Abbreviation for International Telecommunication Union. iW- Abbreviation for industrial television. i-type -Intrinsic semiconductor. i-type semiconductor material-A semieonductor material in which the electron and ho!e densities are effectively equal under conditions of thermal equilibrium. IVR -Abbreviation for integrated voltage regulator. IWW- Abbreviation for intermittent windshield wiper (General Motors, Ford Motor, and Ghrysler Corp.). In an automobile, electronic control of the windshield wiper motor to vary the time interval between wipes.

J

J -Letter symbol for joule. jack-1. A socket to which the wires of a circuit are connected at one end, and into which a plug is inserted at the other end. 2. A type of two-way, or more, concentric contact socket for carrying audio signals. 3. A receptacle into which a mating connector may be plugged. 4. The receptacle that accepts a plug, specifically a phone plug. 5 . A plug-in type terminal widely used in electronic apparatus for temporary connections or those requiring frequent connections and disconnections. A connection is made to a jack simply by plugging a probe or plug attached to a flexible insulated wire or cable into the jack. 6. Receptacle for a plug connector leading to the input or output circuit of a tape recorder or other piece of equipment. A jack matches a specific plug. j a c k bay- Also called patch bay. A panel containing a number of signal jacks (usually standard phone jacks or mini phone jacks), commonly used in studio recording consoles and in equipment racks to provide flexibility in rerouting signals (beyond that provided by normal switches or controls). The jack bay also offers convenience when temporarily connecting certain equipment to a system. or troubleshooting and aligning equipment. jacket- 1. Pertaining to wire and cable, the outer sheath that protects against environment and may also provide additional insulation. 2. An outer, nonmetallic, protective covering applied over an insulated wire or cable. j a c k panel- An assembly composed of a number of jacks mounted on a board or panel. jackscrew-A screw attached to one half of a twopiece, multiple-contact connector and used to draw both halves together and to separate them. jaff -Slang for the combination of electronic and chaff jamming. j a g -In facsimile, distortion caused in the received copy by a momentary lapse in synchronism between the scanner and recorder. jaggies-In-egular edges on something that should look smooth, a byproduct of the method of searching a scene and of too coarse a bit map. jam- 1. In punch-card machines, a condition in the card feed that interferes with the normal travel of the punch cards through the machine. 2. To interfere electronically with the reception of radio signals. j a m input-The presetting or loading of a counter, using inputs provided for the purpose. Also, the establishment of a desired logic state or logic line by the direct application of the appropriate voltage level to the line, regardless of the outputs of other devices connected to it. j a m m e r -An electronic device for intentionally introducing unwanted signals into radar sets to render them ineffective. j a m m e r band -The radio-frequency band where the jammer output is concentrated. It is usually the band

between the points where the intensity is 3 dB down from maximum. j a m m e r finder- Also called bumthrough. Radar that attempts to obtain the range of the target by training a highly directional pencil beam on a jamming source. j a m m e r s t r a c k e d b y azimuth crossings- Semiautomatic strobe processing and tracking that permits automatic detection and tracking on the basis of azimuth information obtained from the jamming signals emanating from an airborne vehicle. jamming -Also called active electronic countermeasures. 1. The intentional transmission of radio signals in order to interfere with the reception of signals from another station. 2. Interference with hostile radio or radar signals for the purpose of deceiving or confusing the operator. It may be accomplished by saturating a receiver with sufficient noise to prevent detection and location of a target, or by deceiving the operator with intentionally misleading signals or false echoes without his knowing that such signals are present. 3. The deliberate radiation, reradiation, or reflection of electromagnetic energy to impair the use of electronic devices, equipment, or systems by the enemy. Equipment may consist of rudimentary cw or noise transmitters, broadband transmitters, or complex systems that generate deceptive signals. jamming effectiveness-The jamming-to-signal ratio, that is, the percentage of information incorrectly received in a test message. JAN specification-Joint Army-Navy specification. The forerunner of present military specifications; generally superseded by the designation MIL. J-antenna-A half-wave antenna fed at one end by a parallel-wire, quarter-wave section having the configuration of a J. Java -A platform-independent programming language invented by Sun Microsystems that is specifically designed for writing programs that can be safely downloaded to a computer through the Internet and immediately run without fear of viruses or other harm to the computer or to files. Using small Java programs (called applets), web pages can include functions such as animations, calculators, and other fancy tricks. J-carrier s y s t e m -A broadband carrier system that provides 12 telephone channels and utilizes frequencies up to about 140 kilohertz by means of four-wire transmission on a single open-wire pair. J-display-Also called J-scan. In radar, a modified A-display in which the time base is a circle and the target signal appears as a radial deflection from it. JEDEC- Acronym for Joint Electron Device Engineering Council. An industry-sponsored organization whose function is to provide a means of standardization for the industry. This encompasses numbering systems, testing methods and techniques, sDecificationsuniformity. 400

JETEC -joined actuator

401

appear on both input terminals; it changes state when all inputs are activated. J and K have no particular meaning, but were selected to avoid conflict with other commonly used symbols.

J

J-dispIuy. CLOCK

and similar attempts on the part of the component manufacturers to assist the users of electronic components. In addition, JEDK attempts to establish a code of ethics for the industry and to offer a set of standards for nonmilitary parts. JETEC --Acronym for Joint Electron Tube Engineering Council. jewel lbearing -A natural or synthetic jewel, usually sapphire, used as a bearing for a pivot or other moving parts of a delicate instrument. jezebel-A system for the detection and classification of submarines. JFET -- Abbreviation for junction field-effect transistor. A semiconductor device that operates by altering the conductivity of a region of the semiconductor (the channel) between two contacts (source and drain) by application of a voltage to a third terminal (gate). The current flow between source and drain is controlled by the gate voltage. In a J E T device, the gate voltage is applied to the channel across a pn junction, in contrast to its application across an insulator in a conventional MOSEET. J E T S are of two types: p channel and n channel, depending on whether the channel is n type or p type. JHG -Abbreviation for Joule heat gradient. jitter- 1. Instability of a signal in either its amplitude or its phase, or both, due to mechanical disturbances or io changes in supply voltage, component characteristics, etc. 2. In relation to cathode-ray tube displays, error in the signal amplitude, phase, or both that results in small, rapid abberations in size or position of the image. 3. Error of synchronization between a facsimile’s transmitter and receiver characterized by a raggedness in the copy. 4. An aberration of a repetitive display, indicating instability of the signal or of the oscilloscope. May be random or periodic, and is usually associated with the time axis. 5. A loss of synchronization caused by electrical or mechanical malfunctions. 6. Type of analog-communication-line distortion caused by a signal’s variation from its reference timing position, which can cause data-transmission errors, particularly at high speeds. This variation can be in amplitude, time, frequency or phase. See flicker, 3; fortuitous telegraph distortion. jittered pulse recurrence f r e q u e n c y -The random variation of the pulse-repetition period. Provides a discrimination capability against repeater-type jammers. J-K flip-flop-A flip-flop with two conditioning inputs (J and K) and one clock input. If both conditioning inputs are disabled prior to a clock pulse, the flip-flop does not change condition when a clock pulse occurs. If the J input is enabled and the K input is disabled, the flip-flop will assume the 1 condition upon arrival of a clock pulse. If the K iniput is enabled and the J input is disabled, the flip-flop will assume the 0 condition when a clock pulse arrives. If both the J and K inputs are enabled prior to the arrival of a clock pulse, the flip-flop will complement, or assume the opposite state, when the clock pulse occurs. The J-K flip-flop is a refinement of the R-S flip-flop with the advantage that it has a determinate state when signals

K

job- 1. A group of tasks specified as a unit of work for a computer. Usually by extension, a job includes all necessary programs, linkages, files, and instructions for the operating system. 2. In a computer, a collection of tasks, grouped and run together in order to perform a specific function. j o b control language-A special computer command language designed for use in batch systems to inform the systems software and computer operator of unique requirements for the running of a computer program. job library-A related series of user-identified, partitioned data sets that serve as the primary source of load modules for a given job. j o b statement-A control statement that identifies the start of a series of job control statements for a single job. j o b step-The carrying out of a computer program explicitly identified by a job control statement. The execution of several job steps may be specified by a job. jogging-Also called inching. Quick and repeated opening and closing of a motor starting circuit to produce slight movements of the motor. Johnson counter- Also called Mobius counter or twisted-ring counter. A counter composed of an N stage shift register with the complement of the last stage returned to the input. It normally has 2N states through which it cycles. It has the distinguishing characteristic that only one stage changes state at each count. See ring counter, 2. J o h n s o n noise-Also called thermal noise. 1. The noise generated by any resistor at a temperature above absolute zero. It is proportionate to the absolute temperature and the bandwidth according to the following formula: N =KT3

where N is the noise power in watts K is Boltzmann’s constant, or 1.38047 x T is he absolute temperature in kelvins B is he bandwidth in hertz 2. A frying or sizzling sound produced by thermal agitation voltages generated in amplifier circuits. It usually occurs in the input circuit (or front end) of an amplifier. Discovered by J. B. Johnson in the late 1920s, this thermal noise may be generated by a resistor at a temperature above absolute zero. It is random noise engendered by thermal agitation. joined actuator-A multiple breaker such that when one pole trips, all trip, but whereas the faulted pole

joint - junction

box

is tripfree, the other poles may be kept maintained by a restraining actuator. joint-A connection between two or more conductors, or the connecting point of two conductors. joint circuit -A communication link in which there is participation by the elements of more than one service, through control, operations, management, etc. joint communications-The common use of communication facilities by two or more services of the same country. Joint electron device Engineering Council See JEDEC.

Joint electron tube Engineering Council -See

JETEC. joint pole-Pole used in common by two or more utility companies. joint use-The simultaneous use of pole, line, or plant facilities by two or more kinds of utilities. Jones plug -A type of polarized connector designed in the form of a receptacle and having several contacts. J o s e p h s o n effect -1. The phenomenon described by Brian Josephson to explain the action of currents through and voltages across hairlike gaps in superconductors. On the basis of theoretical considerations, it is predicted that if two superconductors would be brought close enough together, a current could be made to flow across the gap between them. Under certain conditions, a voltage appears across the gap, and high-frequency radiation emanates from it. This predicted radiation would have a frequency precisely equal to 2eV/h, where V is the measured voltage across the gap. 2. Characteristic of radiation detectors that produce energy that is similar to the energy of superconductive gaps when interacting with photons. joule-1. The work done by a force of 1 newton acting through a distance of 1 meter. The joule is the unit of work and energy in the mksa system. 2. The energy required to transport 1 coulomb between two points having a potential difference of 1 volt. The joule is lo7 ergs. The kilowatt-hour is 3.6 x lo6 joules. 3. A unit of energy of work C V 2 / 2 equal to 1 wattsecond. Energy stored in a capacitor is equal to C V 2 / 2joules or wattseconds, where C is capacitance in farads and V is voltage in volts at the capacitor’s terminals. The letter symbol for joule is J. Joule effect-In a circuit, electrical energy is converted into heat by an amount equal to Z’R. Half of this heat flows to the hot junction and the other half to the cold junction. Joule h e a t -The thermal energy produced as a result of the Joule effect. Joule h e a t gradient -Abbreviated JHG. The rate at which the thermal heat produced by the Joule effect increases or decreases. Joule’s law of electric heating -The amount of heat produced in a conductor is proportional to the resistance of the conductor, the square of the current, and the time. joystick-I. A control device consisting of a handle with freedom of motion in all directions of a plane, connected to potentiometers or other control devices through suitable linkage permitting natural human input of positioning or other information. The term is derived from the joystick of aircraft. 2. A data-entry device used to manually enter coordinate values in special X-, Y-, and Z-input registers. The device consists of a vertically mounted stick or column that can be moved and twisted. When it is moved backward or forward or sideways, coordinate values are stored in the X- and Y-input registers. The Z-input register is varied whenever the

402 joystick is twisted clockwise and counterclockwise. These registers must be scanned by the host computer since joysticks normally do not generate interrupts when they are activated. Usually the joystick is used to move a cursor and/or tracking symbol on the face of the CRT screen. Used mainly for computer games. 3. A type of four-channel pan potentiometer that has a shaft with a handle that can be moved forward and back, left and right, or anywhere in between to direct a single input signal to any of four output channels. J-scan -See J-display. J-scope- Also called class J oscilloscope.A cathoderay oscilloscope that presents a J-display. J/S ratio-A ratio, normally expressed in dB, of the total interference power to the signal-carier power in the transmission medium at the receiver. juice-Slang for electric current. jump- 1. To cause the next instruction to be selected from a specific storage location in a computer. 2. A departure from the normal one-step incrementing of the program counter. By forcing a new value (address) into the program counter, the next instruction can be fetched from an arbitrary location (either further ahead or back). For example, a program jump can be used to go from the main program to a subroutine, from a subroutine back to the main program, or from the end of a short routine back to the beginning of the same routine to form a loop. 3. Transfer of program logic flow by bypassing a number of instructions. The jump can be forward over a positive number of bytes or backward by expressing a negative number of bytes. The jump can be conditional on the status of the accumulator or other registers. jumper- 1. A short length of wire used to complete a circuit temporarily or to bypass a circuit. 2. A direct electrical connection, which is not a portion of the conductive pattern, between two points in a printed circuit. 3. An electrical connection between two points on a printed board added after the intended conductive pattern is formed. 4. A short length of cable used to make electric connections within, between, among, and around circuits and their associated equipment. 5. A length of conductor used to establish connections (often temporary) between two points or to provide a path around a break in a circuit. A jumper can interconnect board to connector, board to board, or power supply to black box unit. 6. A direct electrical connection between two points on a film circuit. Jumpers are usually portions of bare or insulated wire mounted on the component side of the substrate. 7. A patch cable or wire used to establish a circuit, often temporarily, for testing or diagnostics. j u m p e r cable-A short flat cable interconnecting two printed wiring boards or devices. junction- 1. A connection between two or more conductors or two or more sections of a transmission line. 2. A contact between two dissimilar metals or materials (e.g., in a rectifier or thermocouple). 3. A region of transition between p- and n-type semiconductor material. The controllable resultant asymmetrical properties are exploited in semiconductor devices. There are diffused, alloy, grown, and electrochemical junctions. 4. A joining of two different semiconductors or of semiconductor and metal. 5. Optical interface. junction barrier-The opposition to the diffusion of majority carriers across a pn junction due to the charge of the fixed donor and acceptor ions. junction battery-A nuclear type of battery in which radioactive strontium 90 irradiates a silicon pn junction. junction box- 1. A box for joining different runs of raceway or cable, plus space for connecting and branching the enclosed conductors. 2. An enclosed distribution panel

403

junction capacitance

for connecting or branching one or more corresponding electric circuits without the use of permanent splices. capacitance -The total small-signal capacitance between the contacts of an uninstalled semiclonductor die. junction capacitor-A capacitor in which the capacitance is that of a reverse-biased pn junction.

- justification

device where the conductance in the channel between the source and the drain is modulated by a transverse electric field. The field is controlled by a combination of gate-source bias voltage, VGS, and the net drain-source voltage, V D S .

METAL

CONTACTS

so

IN

LOW.RESISTANCE OHMIC CONTACT GATE

Junction capacitor.

SOURCE

junction diode- 1. A two-terminal device containing a single crystal of semiconducting material that ranges from p type at one terminal to n type at the other. It conducts current more easily in one direction than in the other and is a basic element of the junction transistor. Such a diode is the basic part of an injection laser; the region near the junction acts as a source of emitted light. When fabricated in a suitable geometrical form, the junction diode can be used as a solar cell. 2. A pn junction characterized by slower switching speed and higher operating voltage and temperature than the Schottky diode. The fast recovery version of the junction diode turns off faster than the conventional pn junction diode, usually in hundredths of a nanosecond. 3. A semiconductor diode having the property of conducting current more easily in one direction than the other. This device may be made by diffusion of an impurity into a semiconductor crystal to form a junction. Such diodes are the basic elements of an injection laser. Light is emitted from the area near the junction.

PLUG

GLASS

BODY

DUMET PLUG

8

L 3 SILICON DI~FUSED WAFER

Junction diode assembly.

junction FET-A field-effect transistor having one lor more gates that form pn junctions with the channel. ,See also junction field-effect transistor. junction field-effect transistor-Abbreviated J E T . 1. A transistor made up of a gate region diffused into a channel region. The gate element is a region of semiconductor material (ordinarily, the substrate) insulated by a pn junction from the channel, which is material of opposite polarity. When a control voltage i s applied to the gate, the channel is depleted or enhanced, and the current between source and drain is thereby controlled. There is no current when the channel is pinched off. 2. A field-controlled majority carrier

GATE

DRAIN

Junction field-effect transistor.

junction filter-A combination of a high-pass and a low-pass filter that is used to separate frequency bands for transmission over separate paths. For example, junction filters are used to separate voice and canier frequencies at the junction between open-wire and cable so that the carrier frequencies and voice frequencies can be sent over nonloaded and VF-loaded cable pairs, respectively. junction-gate field-effect transistor-A fieldeffect transistor having one or more gate regions that form pn junction(s) with the channel. junction loss-1. In telephone circuits, that part of the repetition equivalent that can be assigned to interactive effects originating at trunk terminals. 2. The transmission loss due to the mismatch of impedance between two types of transmission facilities. See repetition equivalent. junction point-See node, I. junction pole-Pole at the end of a transposition section of an open-wire line or the pole common to two adjacent transposition sections. junction station-A microwave relay station that joins a microwave radio leg or legs to the main, or through, route. junction transistor-A transistor having three alternate sections of p-type or n-type semiconductor material. See also npn transistor; pnp transistor. junction transposition -Transposition located at the junction pole between transposition sections of an open-wire line. junctor -In crossbar systems, a circuit extending between frames of a switching unit and terminated in a switching device on each frame. justification- 1. The act of adjusting, arranging, or shifting digits to the left or right so that they conform to a prescribed pattern. 2. The automatic inserting of blank spaces within text to make the right margin even on a page.

justify

- jute-protected cable

justify-To align data about a particular reference or to produce a text with flush left and right margins (a more printlike appearance). just-operate value -Also called dropout value. The measured functioning value at which a particular relay operates. Contrast just-release value. just-release value -The measured functioning value at which a particular relay releases.

404 just scale-A musical scale formed by three consecutive triads (those in which the highest note of one is the lowest note of the other), each having the ratio 4 :5: 6 or 10:12:15. jute -Cordage fiber (such as hemp) saturated with tar and used as a protective layer over cable. jute-protected cable-A cable having its sheath covered by a wrapping of tarred jute or other fiber.

K-I. Symbol for cathode or dielectric constant. 2. Letter symbol for kelvin or kilo. 3. Abbreviation for luminosity factor. 4. In a calculator, a fixed number (a constant) that can be used repetitively. 4. Symbol for lo3. When referring to bits or words, K = 1024. A 4 K chip is a 4 K-bit chip. A 4 K memory is a 4 K-word memory (typically 4 K bytes). 5. When referring to memory storage capacity, 2"; in decimal notation, 1024. k-Letter symbol for kilo-. kA-L.etter symbol for kiloampere. Ka band-The frequency band from 18 to 31 GHz. Karnaiugh map-A display of a truth table in a way such that reduction (simplification) of a Boolean expression is facilitated. It consists of a rectangular or square array (depending on the number of variables) of "locations" whose coordinates correspond to truth-table inputs. KB or Kb-Abbreviation for kilobyte. 1024 bytes (XI 92 bits). K-band -A radio frequency band extending from 11 to 36 GHz and having wavelengths of 2.73 to 0.83 cm. Kbps-- Abbreviation for kilobits per second. A standard measurement of data rate and transmission capacity. One Kbps equals 1024 bits per second. k c -Abbreviation for kilocycle. Now obsolete. Replaced by kMz. K-carrier system -A broadband carrier system that provides 12 telephone channels and utilizes frequencies up to about 60 kHz by means of four-wire transmission on cable facilities. K-display -Also called K-scan. Modification of a type-A scan, used for aiming a double-lobe system in bearing 0.1elevation. The entire range scale is displaced toward the antenna lobe in use. One signal appears as a double deflection from the range and relative scales. The relative anglitudes of these two pips indicate the amount of error in aiming the antenna. keep-alive anode -An auxiliary electrode that maintains a dc discharge in a mercury-pool tube. It has the disadvantage of reducing the peak inverse voltage rating. keep-alive circuit -In a tr or anti-tr switch, a circuit for producing residual ionization in order to reduce the time for full ionization when the transmitter fires. keep-alive voltage -A dc voltage that maintains a small glow discharge within one of the gap electrodes of a tr tube. This allows the tube to ionize more rapidly when the transmitter fires, thus preventing damage to the ireceiver. keeper-A magnetic conductor, placed over the ends iof a permanent magnet, used to complete the magnet circuit O F a permanent magnet to protect it against demagnetizing influences.

405

Kel-f -Polymonochlorotrifluoroethylene-a plastic used as a high-temperature insulation (-55°C to +135"C). kelvin-Formerly degree Kelvin. A unit of absolute temperature equal to U273.16 of the Kelvin scale temperature of the triple point of water. Letter symbol: K. Kelvin balance -An instrument for measuring current. This is done by sending a current through a fixed and a movable coil attached to one ann of a balance. The resultant force between the coils is then compared with the force of gravity acting on a known weight at the other end of the balance arm. Kelvin bridge- Also called a double or Thompson bridge. A seven-arm bridge for comparing the resistances of two 4-terminal resistors or networks. Their adjacent potential terminals are spanned by a pair of auxiliary resistance arms of known ratio, and they are connected in series by a conductor joining their adjacent current terminals.

ASOUR ------A

Kelvin bridge.

Kelvin scale-Also called absolute scale. A temperature scale using the same divisions as the Celsius scale, but with the zero point established at absolute zero (-273°C or -459"F), theoretically the lowest possible temperature (the temperature at which all molecular motion stops). Kendall effect-A spurious pattern or other distortion in a facsimile record. It is caused by unwanted modulation produced by transmission of a carrier signal. Such modulation appears as a rectified baseband that interferes with the lower sideband of the carrier. Kennelly-Heaviside layer -See Heaviside layer. kenopliotron -A diode-triode vacuum tube within one envelope. The anode of the diode also serves as the cathode of the triode. kenotron -Also called a value tube. 1. A term used primarily in industrial and X-ray fields for a hot-cathode

Keplerian elements (Keps)

- keying wave

vacuum tube. 2. A high-vacuum, high-voltage thermionic diode, used primarily as a high-voltage rectifier. Keplerian elements (Keps) -A collection of data relating to the position of a satellite in its orbit at any given time. This information is interpreted by satellite tracking programs to predict time and duration of satellite passes and directions in which to point antennas. Named for the 19th-century scientist Johannes Kepler. keraunophone -A radio circuit device for audibly demonstrating the occurrence of distant lightning flashes. kerf-The slit or channel or “L” cut in a resistor during trimming by a laser beam or abrasive jet. kernel- 1. A line within a current-carrying conductor along which the magnetic intensity due to the current is zero. 2. The most basic portion of an operating system, usually supporting only task synchronization, scheduling, communication, and the most rudimentary of memory allocation capabilities. It implements software processes and furnishes the means of interprocess communication; usually written in assembly language. 3. The central portion of a program, containing the bulk of its calculations, that consumes the most execution time. Kerr cell-A container filled with a transparent material that, when subjected to a strong electric field, exhibits double refraction. Because the two polarized components of an incident light beam have different phase velocities in the medium, this device can rotate the plane of polarization. When placed between crossed polarizers, the Kerr cell, usually containing nitrobenzene, can act as an extremely high-speed shutter for light beams. Kerr effect-1. An electro-optical effect in which certain transparent substances become double refracting when subjected to an electric field perpendicular to a beam of light. 2. The conversion of plane into elliptically polarized light when reflected from the polished end of a magnet. Kettering ignition system -Inductive system commonly used for internal combustion engines. Employs induction coil, breaker contacts, capacitor, and a suitable power supply, such as a battery. keV -Letter symbol for kiloelectronvolt. key- 1. A hand-operated switching device for switching one or more parts of a circuit. It ordinarily consists of concealed spring contacts and an exposed handle or push button. 2. A projection that slides into a mating slot or groove so as to guide two parts being assembled and assure proper polarization. keyboard- 1. In a calculator, keys for digits 0 through 9, plus additional keys for various functions, such as add, multiply, divide, subtract, clear, memory, etc. 2. That portion of a terminal used to generate the character stream to the computer or other communications device. 3. An array of push-button switches with related functions. Keyboards use standard push-button contact switches, Hall-effect switches, capacitive switches, and many others. Any type of momentary-contact switch suitable in terms of size, current switching capacity, etc., may be used. The electrical signal generated by switch closure is routed to the appropriate circuitry where the action indicated by closure of the keyboard switch is initiated. 4. A series of switches, usually in the form of a typewriter keyboard, that a computer operator uses to communicate with the computer. keyboard computer-A computer whose input employs a keyboard, e.g., an electric typewriter. keyboarding-Entering information (to a word processor) via a keyboard. keyboard-operated transmission -See KOX. keyboard perforator-A mechanism that punches a paper tape from which messages are automatically transmitted by a transmitter distributor. The keyboard is

406 similar to that of a typewriter and can be operated by any trained typist after a few hours’ instruction. As each key is depressed, the tape is punched with corresponding code symbols. keyboard sendheceive-A combination teletypewriter transmitter and receiver with transmission capability from a keyboard only. See KSR. key cabinet-A case installed on a customer’s premises and providing facilities so that different lines to the control office can be connected to various telephone stations. It has signals that indicate originating calls and busy lines. key click -A transient signal sometimes produced when the key of a radiotelegraph transmitter is opened or closed. The transient is heard in a speaker or headphone as a click. key-click filter-Also called a click filter. A filter that attenuates the surges produced each time the keying circuit of a transmitter is opened or closed. keyed adapter -A device that detects a modulated signal and produces a dc output signal whose amplitude varies in accordance with the modulation. In radio facsi,mile transmission, it is used to provide the keying signal for a frequency-shift exciter unit. keyed AGC -Abbreviation for keyed automatic gain control. keyed automatic gain control-Abbreviated keyed AGC. A television automatic gain control in which the AGC tube is kept cut off except when the peaks of the positive horizontal-sync pulse act on its grid. The AGC voltage is therefore not affected by noise pulses occurring between the sync pulses. keyed clamp-A clamping circuit in which a control signal determines the time of clamping. keyed interval-In a periodically keyed transmission system, an interval that starts from a change in state and has a length equal to the shortest time between changes in state. keyed rainbow generator-A color television test instrument that displays the individual colors of the spectrum, separated by black bars, on the picture tube. keyed rainbow signal-A 3.563795-MHz (3.56MHz) continuous sine-wave signal from a color-bar generator that is pulsed on and off. This signal creates a series of different color bars on the screen of the color picture tube. A typical pulse rate (for 10 color bars) is 12 times per 1 horizontal line. keyer- 1. In telegraphy, a device that breaks up the output of a transmitter or other device into the dots and dashes that are used in the code. 2. A radar modulator. keying-1. The forming of signals, such as those employed in a telegraph transmission, by an abrupt modulation of the output of a director by an alternating-current source (e.g., by interrupting it or by suddenly changing its amplitude, frequency, or some other characteristic). 2. Mechanical arrangement of guide pins and sockets, keying plugs, contacts, bosses, slots, keyways, inserts, or grooves in a connector housing, shell, or insert that allows connectors of the same size and type to be lined up without the danger of making a wrong connection. keying chirps- Sounds accompanying code signals when the transmitter is unstable and shifts slightly in frequency each time the sending key is closed. keying frequency -In facsimile, the maximum number of times a second a black-line signal occurs while scanning the subject copy. keying plug contact-A component that is inserted into a cavity of a connector housing or insert to ensure engagement of identically matched components. keying wave -Also called marking wave. The emission that takes place in telegraphic communication

keyless ringing -

407 while the information portion of the code characters is being transmitted. k e y l e s s ringing-A type of machine ringing on a manual switchboard. Ringing is started automatically when the calling plug is inserted into the jack of the called line. keypad-Device with a matrix of keys enabling a user to input (usually numeric) information into another device, as in dialing a touch-tone telephone. k e y pulse -A telephone signaling system in which numbered keys are depressed instead of a dial being turned. k e y pulsing -A switchboard arrangement using a nonlocking keyset for the transmission of pulse signals corresponding to the key depressions. key-pulsing signal -The signal that indicates a circuit is ready for pulsing, in multifrequency and directcurrent key pulsing. keypunch -A keyboard-operated device that punches holes in punch cards to represent data to be input to a computer b y a card reader. keyshelf-A shelf on which are mounted the keys by means of which the operator of a manual telephone switchboard performs switching of one or more of the switchboard circuits. k e y signal -A pseudorandom sequence of two-level pulses used to accomplish enciphering or deciphering processes. master station from which a k e y .&tion--The network radio or television program originates. distortion produced k e y s t o n e distortion -The when a plane target area not normal to the average direction of the beam is scanned rectilinearly with constantamplitude sawtooth waves.

Keystone distortion.

keystone shaped-Wider at the top than at the bottom, or vice versa. keysttoning -The keystone-shaped scanning pattern produced when the electron beam in the television camera tube is at an angle with the principal axis of the tube. See also keystone shaped. keyswitch -In an organ, the switch that is closed to allow a tone from the tone generator to sound when a key is depressed. key telephone- Also called key telephone set. Telephone set having six button keys and used with relay equipment to provide call holding, multiline pickup, signaling, intercommunication, and conference services. key t e l e p h o n e set-A desk telephone with six (illuminated) push-button keys across the set below the dial. The keys may be connected to hold, pick up a central office line, or pick up an intercom line. key t e l e p h o n e system -A versatile station switching system located on a customer’s premises, consisting of one or more multibutton telephone sets and associated equipment. Permits mutual access and control of a number of central office lines, as well as pickup, hold, signal, and intercommunication capability.

k e y up-To turn on a repeater by transmitting on its input frequency. keyway-The mating slot or groove in which a key slides. keyword- 1. Characteristic word is a computer file used to retrieve its contents. 2. A word (with a special meaning) that is recognized by the computer or program. kHt- Abbreviation for kilohertz. A unit of frequency measurement equivalent to 1000 cycles per second; formerly expressed as kilocycles per second, or kc/s. kickback-The voltage developed across an inductance by the sudden collapse of the magnetic field when the current through the inductance is cut off. kickback power Supply-See flyback power supply. kick-sorter -British term for pulse-height analyzer. kidney joint-A flexible joint, or air-gap coupling, located in the waveguide and near the transmittingreceiving position of certain radars. Kikuchi lines-A series of specb-aP lines obtained by the scattering of electrons when an electron beam is directed against a crystalline solid. The pattern may be interpreted to yield information on the structure of the crystal and its mechanical perfection. killer circuit-1. The vacuum tube or tubes and associated circuits in which are generated the blanking pulses used to temporarily disable a radar set. 2. In a transponder, a logic circuit that kills replies to side-lobe interrogations. killer pulse -See suppression pulse. kilo--A prefix representing lo3, or 1000. Letter symbol: k. kiloampere -1000 amperes. Letter symbol: kA. kilobaud -Abbreviated kBd. One thousand baud. kilobit -1024 bits. kilobyte- 1. A standard quantity measurement for disk and diskette storage and semiconductor circuit capacity: 1 kilobyte of memory equals 1024 bytes @-bit characters) of computer memory. 2. 21°, or 1024, bytes, Commonly thought of as 1000 bytes. Abbreviated K and used as a suffix to describe memory size. kilocycle (kc) - 1000 cycles. Generally interpreted as meaning 1000 cycles per second. Obsolete term; replaced by kilohertz (kHz). kiloelectronvolt-1000 electron volts. The energy acquired by an electron that has been accelerated through a voltage difference of 1000 volts. Letter symbol: keV. kilogauss- 1000 gauss. kilogram-Unit of mass. The mass of a particular cylinder of platinum-iridium alloy, called the international prototype kilogram, that is preserved in a vault at Sevres, France, by the International Bureau of Weights and Measures. Letter symbol: kg. kilohertz -lo00 hertz. Letter symbol: kHz. kilohm - 1000 ohms. Abbreviated k or kohm. kilohmmeter-A meter designed for measuring resistance in kilohms. kilounega (kM) -Obsolete prefix for giga- (G), representing io9 or ~,OOO,OOO,OO~. kilomegacycle-Now called gigahertz. One billion cycles per second. kilometer -One thousand meters, or approximately 3280 feet. kilometric w a v e s --British term for electromagnetic waves between 1000 and 10,000 meters in length. kilosecond - 1000 seconds. kilovar- One reactive kilovoltampere, or 1000 reactive voltamperes. Letter symbol: kvar. kilovar-hour- 1000 reactive volt-amperehours. kilovolt -1000 volts. Letter symbol: kV.

kilovoltampere - klystron

+

control grid +

408

+

+

+

+

BUSHING THROUGH INSTRUMENT CASE

Klydonograph gradient recorder.

kilovoltampere - 1000 voltamperes. Letter symbol: kVA. kilovoltmeter -A voltmeter that reads thousands of volts. kilowatt -1000 watts. Letter symbol: kW. kilowatthour -The equivalent energy supplied by a power of 1000 watts for 1 hour. Letter symbol: kWh. kine -Slang term for kinescope recording. kine-klydonograph -An instrument that records the current-time characteristics of a lightning stroke. The instrument records a series of Lichtenberg figures in a manner similar to that of the field gradient recorder. k i n e s c o p e -1. A cathode-ray tube that serves as a picture tube in a television receiver. The signal representing the picture intensity is transmitted to the electron gun grid so that the beam intensity varies with the intensity of the original scene. Deflecting voltages sweep the beam horizontally and vertically until it is synchronized with the scanning of the camera tube. The electron beam then strikes the fluorescent end screen of the tube and the scene is reproduced. 2. A film recording made from a television program on a picture tube and used as a permanent record or for subsequent rebroadcasting.

GLASS NECK SECTIOY

CATHODE GRID-1 GRID 2

CENTERING MAGNET

\

any closed path in a circuit is equal to the algebraic sum of the electromotive forces in that path. (Laws 1 and 2 are also called laws of electric networks.) 3. At a given temperature, the emissive power of a body is the same as its radiation-absorbing power for all surfaces. kit-A prepared package of parts with instructions for assembly and/or wiring a component or chassis (also a small accessory item). klydonograph -A field gradient recording instrument that registers voltages on photographic film in the form of Lichtenberg figures. klystron-An electron tube used as an oscillator or amplifier at ultrahigh frequencies. The electron beam is velocity modulated (periodically bunched) to accomplish the desired results.

ELECTRON BEAM FEEDBACK CAUSES

DEFLECTION YOKE

-

GRiD 3 GRlO 4 GRID 5

Kinescope, 1.

k i n e s c o p e gun-The electron gun in the kinescope. k i n e s c o p e recorder -A camera that photographs television images directly from the picture tube onto motion-picture film. kinetic e n e r g y -Energy that a system possesses by virtue of its motion. Kirchhoff’s laws - 1. The current flowing to a given point in a circuit is equal to the current flowing away from that point. 2. The algebraic sum of the voltage drops in

EXCESS ELECTRONS DISSIPATED IN WATERCOOLED COLLECTOR

Klystron.

klystron control grid -An electrode that controls the emission, or beam current, of a klystron or other velocity-modulated tube.

409 klystrlon f r e q u e n c y multiplier-A two-cavity klystron that has the output cavity tuned to a multiple of the fundamental frequency. klystrlon generator-A klystron tube used as a gen(erator.Its cavity feeds energy directly into a waveguide. kliystron oscillator -An oscillator employing a klystron tube to generate radio-frequency power. klystrlon repeater-A klystron tube operated as an ;amplifierand inserted directly into a waveguide in such a 'way that hcoming waves velocity-modulate the electron stream ernitted from a heated cathode. A second cavity (convertsthe energy of the electron clusters into waves of a much higher amplitude and feeds them into the outgoing ;guide. kM -Abbreviation for kilomega (an obsolete term). Replaced by giga. C --Abbreviation for kilomegacycle. Now replaced by gigahertz. k n e e - I. An abrupt change in direction between two relatively straight segments of a curve, such as the region of a magnietizationcurve near saturation or the top bend of a vacuum-tube characteristic curve. 2. A section between two compzratively straight segments of a curve in which the magnitude of curvature, although of the same sign, is relatively high. 3. The region of maximum curvature. knife-edge diffraction -In radio-wave propaga%ion,an effect by which the atmospheric attenuation of a signal is reduced when the signal is diffracted as it passes over a sharp obstacle such as a mountain ridge. knife-edge pointer (of a meter) -A pointer whose end is flattened and turned edgewise so the smallest dimension or edge is seen. Usually used with mirrorbacked scales to eliminate parallax and increase the accuracy of reading. knife switch-1. A form of air switch in which a moving eliement is sandwiched between two contact clips. The moving element is usually a hinged blade; when it is not, it is removable. 2. A form of switch in which the moviing element, usually a hinged blade, enters or embraces stationary contact clips. k n o b -- A round, polygonal, or pointer-shaped part that is fa.stened to one end of a control shaft so that the shaft can be turned more easily. The knob sometimes indicates the degree of rotation also. knockrer-A term used with some fire-control radars to indicate a subassembly comprising synchronizing and triggering circuits. It drives the rf pulse-generating equipment in the transmitter and also synchronizes the cycle of operation with the transmitted pulse in range units and indicators. knock:out-A removable portion in the side of a box or cabinet. During installation it can be readily taken out

klystron f r e q u e n c y multiplier

-

with a hammer, screwdriver, or pliers so the raceway, cables, or fittings can be attached. knot-One nautical mile (6,OSO.ZO feet, 1852 meters, or 1.15 statute miles) per hour. Kooman antenna-A vertical m a y of horizontal full-wave dipoles that are driven by transposed twoconductor line and backed by a parasitic reflecting curtain or horizontal dipoles. Kovar -An iron-nickel-cobalt alloy with a coefficient of expansion similar to that of glass and silicon and thermal characteristics similar to those of alumina. It is used as a material for headers and in glass-to-metal seals. Kovadglass packages are used extensively in hybrid construction to preserve hermetic sealing. KOX -Acronym for keyboard-operated transmission. A station equipped with a KOX system can turn on the transmitter and turn off the receiver simply by typing on the station's keyboard. When the operator ceases typing, the transmitter automatically turns off, and the receiver turns on after some preset delay, kraft paper -Relatively heavy, high-strength sulfate paper used for electrical insulating material. (Capacitor tissue is kraft paper of normal thickness equal to 0.002 inch, or 50 pm, or less.) K-scan -See K-display. K-series-A series of frequencies in the X-ray spectrum of an element. KSR -Abbreviation for keyboard send-receive unit. A combination transmitter and receiver with transmission capability from the keyboard only (teletypewriter term). Refers to a terminal device (teletype or similar) having only a keyboard for sending and a printer for receiving, Le., no paper or magnetic tape equipment, but which is useful for conversational time-sharing and inquiryresponse applications. KU band -1. A band of microwave frequencies between 11 and 13 GHz. 2. Also called K band. A band of frequencies that extends from 11.7 to 12.7 GHz. The band is separated into two portions: 11.7 to 12.2 GHz (fixed satellite services -intended for point-to-point services) and 12.2 to 12.7 GHz (for broadcasting satellite service or DBS). 3. The frequency band from 10.9 to 17 GHz. kurtosis-The degree of curvature of the peak of a probability curve. kV-Letter symbol for kilovolt. kVA- Letter symbol for kilovoltampere. kvar -Letter symbol for kilovar. kW-Letter symbol for kilowatt. kWh -Letter symbol for kilowatthour. kymograph -An instrument for recording wavelike oscillations of varying quantities for medical studies.

L

lacquer original -Also called lacquer master. An original recording made on a lacquer surface to be used as a master. lacquer recording-Any recording made on a lacquer medium. ladder attenuator-A series of symmetrical sections used in signal generators and other devices in which voltages and currents must be reduced in known ratios. They are designed so that the required ratio of voltage loss per section is obtained with image-impedance operation. The impedance between any junction point and common ground in a ladder attenuator is half the image impedance.

L -Symbol for coil, lambert, or inductance. label- 1. A code name used to identify or classify a name, term, phrase, or document. 2. One or more characters that serve to identify an item of data. 3. A numerical value or a memory location in the programmable system of a computer. The specific absolute address is not necessary since the intent of the label is a general destination. Labels are a requisite for jump and branch instructions. 4. A number or letter or a name given to a program statement so that the computer can find it later. 5. A name used in source code to identify an instruction or executable statement in computer programs. 6. A block at the beginning or at the end of a volume or file that identifies, characterizes, andlor delimits that volume or file. A label is not considered to be part of a file. label group-A collection of continuous label sets of the same label type. labile oscillator -A local oscillator whose frequency is remote controlled by a signal received from a radio or over a wire. laboratory power supply-A regulated dc source having (a) less than 10-kV output at up to 500 W, (b) output adjustable over a wide range, usually down to zero, (c) regulation on the order of fO.O1 percent static line and load. labyrinth -Speaker enclosure with absorbing air chambers at the rear to eliminate acoustic standing waves. A mazelike construction extends the air column. Resonances are tamed by heavy damping material. labyrinth l o u d s p e a k e r -Loudspeaker mounted in an acoustic baflle having air chambers designed to prevent acoustic standing waves. lacing-A network of fine wire surrounding or covering an area to be protected, such as a safe, vault, or glass panel, and connected into a closed-circuit system. The network of wire is concealed by a shield, such as concrete or paneling, in such a manner that an attempt to break through the shield breaks the wire and initiates an alarm. lacing and harnessing -Also called bundling. A method of grouping wires by securing them in bundles or designated patterns. lacing cord or twine-Cord used for lacing and tying cable forms, hookup wires, cable ends, cable bundles, and wire harness assemblies. Available in various materials and impregnants. lacing tape-Flexible, flat, fabric tape for tying harnesses and wire bundles, securing of sleeves and other items, and general lacing and typing applications. lacquer disc- Also called cellulose-nitrate disc. A mechanical recording disc, usually made of metal, glass, or paper and coated with a lacquer compound often containing cellulose nitrate. lacquer master-See lacquer original.

f

M e r attenuator.

ladder diagram -1. A diagram that shows actual component symbols and the basic wiring configuration of a relay logic circuit (as opposed to a logic diagram). 2. An industry standard for representing control logic relay systems. 3. Electrical engineering technique to schematically illustrate functions in an electrical circuit (relays, switches, timers, etc.) by diagramming them in a vertical sequence resembling a ladder. 4. See contact symbology diagram. ladder network- Also called series-shunt network. 1. A network composed of H-, L-, T-, or pi networks connected in series. 2. A series of film resistors with values from the highest to the lowest resistor reduced in known ratios. MFOT- Coded weather broadcasts issued by the U.S. Weather Bureau for the Great Lakes region. They are broadcast every 6 hours by marine radiotelephone broadcasting stations on their assigned frequencies. lag -1. The displacement in time, expressed in electrical degrees, between two waves of the same frequency. 2. The time between transmission and reception of a signal. 3. In a television camera tube, the persistence of the electrical-charge image for a time interval equal to a few frames. 4. A time difference between the occurrence of two events. 410

41 1

lagged-demand meter-A meter in which there is a characteristic time lag, by either mechanical or thermal means, before maximum demand is indicated. lagging current-The current flowing in a circuit that is mostly inductive. If the circuit contains only inductance, the current lags the applied voltage by 90”. Because of the characteristics of an inductance, the current ‘does not change direction until after the corresponding voltage does. lagging load- A predominantly inductive loadi.e., one in which the current lags the voltage. lag-lead -Also called lead-lag. A circuit whose response imludes lag components and their derivatives. lambda-Greek letter h, used to designate wavelength measured in meters. lambda diode -A simple two-terminal device cou,sisting of a. pair of complementary depletion-mode juncition field-effect transistors that can be fabricated more (easily than conventional negative-resistance devices. It Isan be integrated on a single chip or with bipolar and MOS devices on the same chip. Unlike tunnel diodes, .which are llimited to a narrow negative-resistance range, :lambda diodes can be produced with a wide range of charactenktics. lambda wave -An electromagnetic wave propa;gated over the surface of a solid that has a thickness Icomparable to the wavelength of the wave. lambetit-A unit of luminance (photometric brightness) equal to lin candela per square centimeter and, therefore, equal to the uniform luminance of a perfectly llifising surface emitting or reflecting light at the rate of 1 lumen per square centimeter. The lambert also is the average luminance of any surface emitting or reflecting llight at the rate of 1 lumen per square centimeter. For the general c,ase, the average must take account of variation of luminance with angle observation, also of its variation from point to point on the surface considered. Letter symbol: L. IambetTian -A radiance distribution that is uniform in all directions of observation. Lambtert’s law of illumination-The illumination of a surface on which the light falls normally from a point source is inversely proportional to the square of the distance of the surface from the source. If the normal to rhe surface makes an angle with the direction of the rays, the illumination is proportional to the cosine of that angle. laminar flow-A directed stream of filtered air moved constantly across a clean work station, usually parallel to the workbench surface. laminate -A product made by bonding together two or more layers of material. laminated-Made of layers. laminated contact-A switch contact made up of a number of laminations, each making contact with an opposite conducting surface. laminated core-An iron core for a coil, transformer, annature, etc. It is built up from laminations to minimize the effect of eddy currents. The sheet iron or steel laminations are insulated from each other by surface oxides or by oxides and varnish.

lagged-demand meter

- landless hole

laminated record --A mechanical recording medium composed of several layers of material (normally a thin face of material on each side of a core). lamination --A single stamping of sheet material used in building up a laminated object such as the core of a power transformer. Lamont’s law-The permeability of steel at any flux density is proportional to the difference between the saturation value of the flux density and its value at the point in question. This law is only approximately accurate and is not true for the initial part of the magnetization curve. lamp-1. A generic term for a human-made source of light. By extension, the term is also used to denote sources that radiate in regions of the spectrum adjacent to the visible range. 2. A device for producing light. lamp bank- An arrangement of incandescent lamps commonly used as a resistance load during electrical tests. lamp cord- 1. A twin conductor, either twisted or parallel, used for connecting floor lamps and other electric appliances to wall outlets. 2. Flexible stranded conductor cord, rubber or plastic insulated, used in wiring of lamps, household fans, and similar appliances. Not subject to hard usage. lamp holder-A lamp socket. lamp housing -A device designed to concentrate and direct a light source by enclosing the source in it and using a concave reflector to direct the light through its only opening. lamp j a c k -Special electronic electromechanical component having a frame that holds a lamp and has the contact springs and terminals for applying power to the lamp. Used extensively in jack panels and other types of telephone equipment as a visual-indicating signal device. Lampkin oscillator-A variation of the Hartley oscillator. Its distinguishing feature is that an approximate impedance match is effected between the tank and gridcathode circuits. lamp receptacle-A device that supports an electric lamp and connects it to a power line. LAN-Abbreviation for local area network. 1. A data communications network spanning a limited geographical area, such as an office, an entire building, or industrial park. It provides communication between computers and peripherals. 3. A baseband or broadband interactive bidirectional communication system for voice, video, or data use on a common cable medium. The network uses some type of switching technology and does not use commoncarrier circuits, although it may have gateways or bridges to other public or private networks. land-1. The surface between two adjacent grooves of a recording disc. 2. Also called boss, pad, terminal point, blivet, tab, spot, donut. In a printed circuit board, the conductive area to which components or separate circuits are attached. It usually surrounds a hole through the conductive material and the base material. 3. A portion of a conductive pattern usually, but not exclusively, used for the connection andlor attachment of components. 4. Widened conductor area on the major substrate used as an attachment point for wire bonds or the bonding of chip devices. Landau damping -The damping of a space-charge wave by electrons moving at the phase velocity of the wave. landing beacon -The radio transmitter that produces a landing beam for aircraft. See also landing beam. landing beam -A highly directive radio signal projected upward from an airport to guide aircraft in making a landing during poor visibility. landless hole-A plated-through hole without a land(s).

landline

- large-signal short-circuit forward-current t r a n s f e r ratio

landline -A telegraph or telephone line passing over land, as opposed to submarine cables. landline facilities-Domestic communications common-carrier’s facilities that are within the continental United States. landmark beacon -Any beacon other than an airport or airway beacon. land mobile service-A radio service in which communication is between a base station and land mobile stations or between land mobile stations. land mobile station -A two-way mobile station that operates solely on land. land radio positioning station -A station in the radio positioning service, not intended to be operated while in motion. land return -Radiation reflected from nearby land masses and returned to a radar set as an echo. lands-Bonding points used in the manufacture of microelectronic circuits. landscape-In word processing, printing a page horizontally across the width of the paper. land station -A permanent, or fixed, station. land transportation radio services-Radiocommunication services whose transmitting facilities include fixed, land, or mobile stations, operated by and for the sole use of certain land transportation carriers. Langevin ion -An electrified particle produced in a gas by an accumulation of ions on dust particles or other nuclei. Langmuir dark space -The nonluminous region surrounding a negatively charged probe inserted into the positive column of a glow or arc discharge. language -1. A set of computer symbols, with rules for their combination. They form a code to express information with fewer symbols and rules than there are distinct expressible meanings. 2. A format for computer programs. Ultimately, computers receive their instructions in machine language, binary codes whose meanings are specific to each computer. Machine codes are usually written in hex or octal for easier use by humans. Highlevel languages, such as BASIC, allow programs to be written in fairly human terms (such as PRINT “NOW IS THE TIME”) that are then translated into a sequence of machine codes. 3. A system for representing information and communicating it between people, or between people and machines. 4. A definition of the elements and syntax within which a computer program must be encoded. 5. The means by which people communicate with a computer. language converter -A data-processing device designed to change one form of data, i.e., microfilm, strip chart, etc., into another (punch card, paper tape, etc.). language translation -The process performed by an assembler, compiler, or other routine that accepts statements in one language and converts them to equivalent statements in another language. language translator -A computer system program that translates text written in one language to another language. Assemblers, interpreters, and compilers are examples of language translators. L-antenna- An antenna consisting of an elevated horizontal wire to which a vertical lead is connected at one end. lanyard -A device that is attached to certain quickdisconnect connectors and that permits uncoupling and separation of connector halves by a pull on a wire or cable. lap - 1. A rotation plate covered with liquid abrasive, used for grinding quartz crystals. 2. A fire-resistant, untwisted, ribbonlike form of asbestos felt made from

412

slivers of asbestos fiber blended with cotton or other organic fibers. Used as a wrapping on wire and cable. LAP-Abbreviation for Link Access Protocol. The data link layer protocol that is used in X.25-based networks in setting up channels between data termination equipment and data communication equipment. lap computer-A battery-operated computer, small and light enough to be operated on the user’s lap. lap dissolve- In motion pictures or television, simultaneous transition in which one scene is faded down and out while the next scene is faded up and in. lapel microphone-A microphone worn on the user’s clothing. lap joint-The connecting of two conductors by placing them side by side so that they overlap. Laplace’s law-The strength of the magnetic field at any given point due to any element of a current-carrying conductor is directly proportional to the strength of the current and the projected length of the element, and is inversely proportional to the square of the distance of the element from the point in question. Laplace transform -A mathematical substitution whose use permits the solution of a certain type of differential equation by algebraic means. lapping -1. Bringing quartz crystal plates up to their final frequency by moving them over a flat plate over which a liquid abrasive has been poured. 2. Grinding and polishing such products as semiconductor blanks in order to obtain precise thicknesses or extremely smooth, flat, polished surfaces. laptop- A small portable computer. Sometimes distinguished as larger than a notebook computer, but sometimes also used as a synonym for notebook computer. lap winding-An armature winding in which opposite ends of each coil are connected to adjoining segments of the commutator so that the windings overlap. lap wrap-Tape wrapped around an object in an overlapping condition. large-scale integrated circuit -An integrated circuit that contains 100 gates or more in a single chip, resulting in an increase in the scope of the function performed by a single device. large-scale integration-Abbreviated LSI. 1. The simultaneous achievement of large-area circuit chips and optimum density of component packaging for the express purpose of cost reduction by maximization of the number of system interconnections made at the chip level. 2. Monolithic integrated circuits of very high density. Such circuits typically have on a single chip the equivalent of about 200 to thousands of simple logic circuits. The term sometimes describes hybrid ICs built with a number of MSI or LSI chips. 3. A classification of ICs by size, applicable to chips containing more than 100 gates or circuits of equivalent complexity. 4. The technology that produces microcircuits with at least 100 active devices on a single chip. Functional blocks that include several op amps and other devices are examples of LSI devices. large-signal c h a r a c t e r i s t i c s -The characteristics of an amplifier when rated (full) output signals are produced. large-signal dc current gain-The dc output current of a transistor with the dc output circuit shorted, divided by the dc input current producing the dc output current. large-signal power gain-The ratio of the ac output power to the ac input power under specified largesignal conditions. Usually expressed in decibels (dB). large-signal short-circuit forward-current transfer ratio-In a transistor, the ratio under specified test conditions of a change in output current to the corresponding change in input current.

large-signal voltage gain - laser diode coupler

413

iarge-signal voltage gain -The ratio of the output voltage swing of an operational amplifier to the change in input voltage required to drive the output from zero to this voltage. Larmor orbit-The path of circular motion of a charged particle in a uniform magnetic field. The motion of the particle is unimpeded in the direction of the magnetic field, but motion perpendicular to the direction of the field is always accompanied by a force perpendicular to the direction of motion and the field. laryngaiphone -Also called a throat microphone. A microphone applied to the throat of a speaker to pick up voice vibrations directly. It is very useful in noisy locations because it picks up only the speaker’s voice -no outside noises. LASCR -Abbreviation for light-activated siliconcontrolled rectifier. 1. A pnpn device in which incident Light performs the function of gate current; three of the four semconductor regions are available for circuit connections. A. photoswitch. 2. A semiconductor device that is triggeIed into conduction when the light falling on the base-collector photodiode junction exceeds a given threshold level. Operation of the LASCR is similar to the silicon-controlled rectifier, with the major difference being thalt an external resistance between gate and cathode {(inaddition to bias voltage and current) determines light sensitivity. A positive electrical signal applied to the gate (can be used to trigger the LASCR, as well as to modify the light sensitivity.

independently of each other, and consequently there is no definite phase relationship among the vibrations in the resultant beam. The light is incoherent. The laser, by means of an optical resonator, forces the atoms of the material of the resonator to radiate in phase. The emitted radiation is stimulated by the excitation of atoms to a higher energy level by means of energy supplied to the device. In the microwave region, the corresponding device is called a maser, and hence the laser is also known as a light maser. 2. A device for producing light by emission of energy stored in a molecular or atomic system when stimulated by an input signal. 3. A mechanically designed semiconductor junction that will optically pump (amplify light) short pulses of high-energy coherent radiation. 4. A device that produces a coherent monochromatic (single wavelength) collimated beam of concentrated light in which the subatomic particles that constitute the beam, known as photons, travel on a parallel axis. Scientists believe that a beam produced by a 5-megawatt laser would be able to melt objects in space at distances exceeding 5000 miles (8045 km).

COOLANT INLET

#

+ l I

I

ANODE

ANODE

CATHODE

I I

GATE

Junctions.

Symbol.

Anode characteristic.

LASCR. LASCS-Abbreviation for light-activated siliconcontrolled switch. 1. A device similar to an LASCR, except that all four semiconductor regions are accessible. 2. A semiconductor device that combines the LASCR and the planar silicon photoswitch (PSPS). Having four terminals, the LASCS can be triggered by light positive signals (at the gate terminal) and negative signals (at the anode gate terminal). l a s e r - 1. A device for transforming incoherent light of various frequencies of vibration into a very narrow, intense beam of coherent light. The name is derived from the initial letters of “light amplification by stimulated emission of radiation.” In the emission of ordinary light, the molecules or atoms of the source emit their radiation

Laser.

laser basic mode-The primary or lowest-order fundamental transverse propagation mode for the emitted light wave of a laser, the emitted energy normally having Gaussian (bell-shaped) distribution in space and being in a single beam, with no side lobes. laser bonding - 1. A process that forms a metal-tometal fastened union, using a laser heat source to join conductors. 2. Effecting a metal-to-metal bond of two conductors by welding the two materials together using a laser beam for a heat sonrce. laser cavity- An optically resonant and hence mode-selecting low-loss strncture in which laser action occurs through the buildup of electromagnetic field intensity upon multiple reflection. l a s e r diode -Abbreviated LD. A junction diode, consisting of positive and negative canier regions with a pn transition region (junction), that emits electromagnetic radiation (quanta of energy at optical frequencies) when injected electrons under forward bias recombine with holes in the vicinity of the junction. In certain materials, such as gallium arsenide, there is a high probability of radiative recombination producing emitted light, rather than heat, at a frequency suitable for optical waveguides. Some light is reflected by the polished ends and is trapped to stimulate more emission. See diode laser; injection laser diode. laser diode coupler-A coupling device that enables the coupling of light energy from a laser diode

Laserdisc

- latch-in relay

(LD) source to an optical fiber or cable at the transmitting end of an optical fiber data link. The coupler may be an optical fiber pigtail expoxied to the LD. Synonym: LD coupler. Laserdisc -A laser-read optical video disc system that can hold thousands of video images and hours of sound. A 12-inch plastic disc used to store video, audio, and other data for playback on a video disc player and video monitor. laser Doppler velocimeter-A laser device utilizing either optical heterodyning or scanning interferometry to measure flow velocities by means of the Doppler shift. laser drill -A system that uses a laser as the source in the evaporation of localized areas as small as 0.00025 cm in diameter of hard materials such as gemstones and tungsten. A pulsed ruby laser is most commonly used in this type of system. laser dyes -Class of organic dyes that emit coherent radiation over a wide spectral range. laser fiber-optic transmission system-A system consisting of one or more laser transmitters and associated fiber-optic cables. During normal operation the laser radiation is limited to the cable. laser head-A module containing the active laser medium, resonant cavity, and other components within one enclosure, not necessarily including a power supply. laser holographic camera -A camera system that has a laser, usually of the pulsed ruby type, as a light source; holographic optics; a plate; and a plate holder. It is used often in the laboratory or in production areas for analysis and detection. The laser’s nanosecond exposure time is most efficient in freezing moving particles in a permanent hologram for convenient analysis. laser linewidth-In the operation of a laser, the frequency range over which most of the laser beam’s energy is distributed. laser printer-A printer whose images are formed by laser light impinging on a light-sensitive drum like that of a photocopy machine; where the light strikes the drum, it will hold xerographic ink for transfer to a sheet of paper. laser protective housing -A protective housing for a laser to prevent human exposure to laser radiation in excess of an allowable established or statutory emission limit for the appropriate class. Parts of the housing that can be removed or displayed and not interlocked may be secured in such a way that removal or displacement of the parts requires the use of special tools. laser pulse length-Also called laser pulse width. The time duration of the burst of electromagnetic energy emitted by a pulsed laser. It is usually measured at the half-power points, Le., on a plot of pulse power developed versus time, the time interval between the points that are at 0.5 of the peak of the power curve. laser pulse width-See laser pulse length. laser rangefinder- A portable instrument that measures the distance between itself and its target by determining the amount of time it takes for a pulsed laser beam to travel to the target and be reflected back to the instrument. A telescope is used to aim the beam, and a photomultiplier detects the reflected pulse. laser ranger-A device similar to conventional radar but using high-intensity light rather than microwaves. laser soldering -A selective soldering technique employing a programmable laser system. The system automatically makes and places solder preforms on one panel while simultaneously laser soldering pins on a second panel. The laser soldering system is effective for high-volume selective soldering of wire-wrapping pins to backplanes, power planes, and PCBs.

414

laser trim -The adjustment (upward in resistance) of a film resistor value by applying heat from a focused laser source to remove material, i.e., to cut a kerf. laser trimming -An IC trimming technique that involves focusing a laser on the die to disconnect resistors. laser welder -A system, similar to a laser drill, that uses the heat from a pulsed laser to weld metals. Because of the rapidity and localization with which the welding takes place, metals of vastly dissimilar melting points can be welded with this system. laser welding -Process in which thermal energy released by a laser impinging on the surface of a metal is conducted into the bulk of the metal workpiece by thermal conduction, bonding component leads to highly conductive materials, such as copper printed circuitry. lasing -1. The phenomenon that occurs when resonant frequency controlled energy is coupled to a specially prepared material, such as a uniformly doped semiconductor crystal that has free-moving or highly mobile, loosely coupled electrons. As a result of resonance and the imparting of energy by collision or close approach, electrons are raised to highly excited energy states; when they move to lower states, they cause quanta of high-energy electromagnetic radiation to be released as coherent light waves. This action takes place in a laser. 2. A unique mode of light production by stimulated emission from excited atoms. The uniqueness of the lasing process is that the light thereby generated tends to be a single frequency, coherent in time and space. lasing condition or state-The condition of an injection laser corresponding to the emission of predominantly coherent or stimulated radiation. latch-1. A feedback loop used in a symmetrical digital circuit (such as a flip-flop) to retain a state. 2. A simple logic storage element. The most basic form consists of two cross-coupled logic gates that store a pulse applied to one logic input until a pulse is applied to the other input; thus, the complementary information is stored in the latch. 3. A name commonly used to refer to a flipflop (usually a D type) when used for data storage, as opposed to counting and logic functions. 4. To lock into a certain location or state. latching-A technique for storing an event such as the momentary breaking of a perimeter circuit. The fact that the event has occurred will be available until the latched circuit has been reset. See alarm hold. latching current-The minimum value of principal current required to maintain a thyristor in the on state after switching from the off state to the on state has occurred and the trigger signal has been removed. latching relay-Also called bistable relay. 1. A relay with contacts that lock in either the energized or deenergized position, or both, until reset either manually or electrically. 2. A relay with two separate coils, one of which must be energized to change the state of the relay, which will remain in either state without the need for external power. 3. A relay that includes a means of holding the state of the relay in the last or latched position. In effect, the relay has a memory, because the contacts remain open or closed when the coil is not actuated. To change state, the latching relay coil must be reenergized. latching sensor-A solid-state Hall-effect sensor that has a plus (south pole) maximum and minimum operate point, and a minus (north pole) maximum and minimum release point. Thus, when the sensor is operated with a south pole, it will stay in the operated condition even with removal of the south pole magnet and will release only in the presence of a north pole. latch-in relay-Also called locking relay. A relay with contacts that remain energized or deenergized until reset manually or electrically.

415

latch mode

LATCH ---L

LOAD

BUTTON

Latch-in reby.

latch mode-A mode of operation for a storage circuit in which all encoder contact closures, even momentary ones, are latched “on.” latch-up-1. A condition in which the collector voltage in a given circuit does not return to the supply voltage when a transistor is switched from saturation to cutoff. Instead, the collector finds a stable operating point in the avalanche region of the collector characteristics. 2. An unintended stable circuit mode that will not revert to a previous intended circuit mode after removal of a s,timulus such as a spurious signal or radiation. The effect is usually caused by parasitic circuit elements. 3. The characteristic of some op amps to remain in positive or negative saturation after their maximum differential input voltage is exceeded. 4. The switching of an electronic circuit to an unintended mode by improper voltage a.pplication. 5. An undesirable phenomenon in which either a pnpn or an npnp thyristor-type parasitic structure suddenly turns to an on state, thereby bypassing or shorting o’ut portions of an IC. latch voltage -The effective input voltage at which a1 flip-flop changes states. late contacts-In a relay, contacts that open or close after other contacts when the relay operates. latency- 1. In a serial storage computer system, the time necessary for the desired storage location to appear under the drum heads. 2. In computers, the time required tlo estabhh communication with a specific storage location, not including transfer time, Le., access time less word time. 3. A state of seeming inactivity, such as that occurring between the instant of stimulation and the beginning of response. 4. A delay encountered in a computer when waiting for a specific response. Latency is caused by propagation delays and the queuing of disks or tapes when randomly addressed. latency time-The time required to shift to any given bit (word) in a serial memory, such as in CCDs and bubble memories. latent image-A stored image (e.g., the one contained in the charged mosaic capacitance in an iconoscope). lateral c h r o m a t i c aberration -Aberration that affects the sharpness of images off the axis. This occurs because different colors produce different magnifications. lateral compliance -The force required to move the reproducing stylus from side to side as it follows the modulation on a laterally recorded record. lateral’-correctionmagnet -In a three-gun picture tube, an auxiliary component used for positioning the blue beam horizontally so that beam convergence will

- lay

be obtained. It operates on the principle of magnetic convergence and is used in conjunction with a set of pole pieces mounted on the focus element of the blue gun. lateral forced-air cooling --A method of heat transfer that employs a blower to produce side to side circulation of air through or across the heat dissipators. lateral loss-A power loss, expressed in decibels, due to the deviation from optimum coaxial alignment of the ends of separable optical conductors. lateral recording -A mechanical recording in which the groove modulation is perpendicular to the direction of motion of the recording medium and parallel to its surface. latex-Rubber material used for insulation of wire. lattice -1. In navigation, a pattern of identifiable intersection lines placed in fixed positions with respect to the transmitters that establish them. 2. The geometrical arrangement of atoms in a crystalline material. lattice network-A network composed of four branches connected in series to form a mesh. Two nonadjacent junction points serve as input terminals, and the remaining two as output terminals. lattice structure-In a crystal, a stable arrangement of atoms and their electron-pair bonds. lattice-wound coil-See honeycomb coil. launch angle-In an optical fiber or fiber bundle, the angle between the input radiation vector, i.e., the input light chief ray, and the axis of the fiber radiation vector, Le., the axis of the fiber or fiber bundle. If the ends of the fibers are perpendicular to the axis of the fibers, the launch angle is equal to the angle of incidence when the ray is external and the angle of refraction when initially inside the fiber. launch complex-The entire launch, control, and support system required for launching rockets. launching -The transferring of energy from a coaxial cable or shielded paired cable in a waveguide. lavalier microphone-A microphone with acoustical and vibration-isolation properties suiting it to use for speech pickup from a position on the speaker’s chest. Lavalier mikes are fitted with a band or strap for hanging around the neck, and are frequently used when it is important that the mike not be conspicuously visible (as to a TV audience). The use of this mike frees the speaker’s hands and allows a certain amount of freedom to move about. lawn mower- 1. In facsimile, a term often used when referring to a helix-type recorder mechanism. 2. A type of I-€ preamplifier used with a radar receiver. law of electric charges-Like charges repel; unlike charges attract. See also Coulomb’s law. law of electromagnetic induction -See Faraday’s laws, 3. law of electromagnetic s y s t e m s -Every electromagnetic system tends to change its configuration so that the flux of magnetic induction will be a maximum. law of electrostatic attraction -See Coulomb’s law. law of magnetism -Like poles repel; unlike poles attract. law of normal distribution-The Gaussian law of the frequency distribution of any normal, repetitive function. It describes the probability of the occurrence of deviants from the average. law of reflection-The angle of reflection is equal to the angle of incidence--.e., the incident, reflected, and normal rays all lie in the same plane. laws of electric networks-See Kirchhoff s laws, 1 and 2. lay- 1. Pertaining to wire and cable, the axial distance required for one cable conductor or conductor strand

layer

- layout

416

to complete one revolution about the axis around which it is cabled. 2. The distance between successive points where the same strand (or insulated conductor) when twisted with one or more strands (or insulated conductors) presents itself in the same position. 3. The length measured along the axis of a wire or cable required for a single strand (in stranded wire) or conductor (in cable) to make one complete turn about the axis of the conductor or cable. layer- 1. The consecutive turns of a coil lying in a single plane. 2. One of several films in a multiple-film structure on a substrate. layer-to-layer adhesion -The tendency for adjacent layers of recording tape in a roll to adhere, particularly after prolonged storage under conditions of high temperature and/or humidity.

layer-to-layer signal transfer -The magnetization of a layer of tape in a roll by the field from a nearby recorded layer. The magnitude of the induced signal tends to increase with storage time and temperature, and to decrease after the tape is unwound. These changes are a function of the magnetic instability of the oxide. layer-to-layer spacing -The thickness of dielectric material between adjacent layers of conductive circuitry in a multilayer printed board. layer winding -A coil-winding method in which adjacent turns are placed side by side and touch each other. Additional layers may be wound over the first and are usually separated by sheets of insulation. layout- 1. Diagram indicating the positions of parts on a chassis or panel. 2. The actual positions of the parts themselves. 3. The topological arrangement of conductors

FRONT GLASS

TRANSPARENT ELECTRODES

FRONT POLARIZER (FIELBEFFECT TYPE ONLY)

BACK. GLASS

LIOUID CRYSTAL MATERIAL CONNECTIONAREA

FRONT POLARIZER (FIELD-EFFECT TYPE 0

i

BACK GLASS

BACK POLARIZER (FIELO-EFFECT TYPE]

CONTACT TO SEGMENl

(FIELD EFFECT ONLY

Construction

BCD INPUT

BACKPLANE ORIVER

D

j Drive electronics

LCD.

1

,417 and comlponents in the design of integrated circuits. It precedes the artwork. 4. A visual representation of a complete physical entity, usually to scale. layout wiring drawing -A type of circuit diagram, made to show explicitly each wire, its gage, color coding, and terminations. lay-up -The technique of registering and stacking layers of a multilayer board before the laminating cycle. L-band-1. Microwave band in which the wavelengths are at or near 23.5 cm. 2. A radio-frequency band (of 390 to 1550 MHz and corresponding wavelengths of '77 to 19 cm. Used for mobile communications. -carrier system -A telephone carrier system employed on coaxial-cable systems and microwave lineof-sight LINE END OF FIELD

262-% LINES PER FIELD

-

HORIZ0NTP.L-

Scanning lines.

scanning linearity -:h television, the uniformity of the scanning speed during the trace interval. scanfling-line f r e q u e n c y -The number of scanning lines per second. See also stroke speed. scanning loss-In a radar system employing a scanning antenna, the reduced sensitivity that occurs in

scatter read - S c h o t t k y

668 MOST OF ENERGY

?

Qy

SEVERAL HUNDRED

\ C,R2 = C,R, C,R,=C,R,

Schering bridge. Scatter propagation.

scatter read -The ability of a computer to distribute data into several memory areas as it is being entered into the system from magnetic tape. SCC -Abbreviation for spark control computer. An analog electronic system (Chrysler Corp.) that accurately controls spark timing in response to various inputs, including engine temperature, manifold pressure, air temperature, and air pressure. Used with EGR, it provides for cleaner exhaust and better fuel economy. scc wire -Abbreviation for single-cotton-covered wire. SCEPTRON -Acronym for spectral comparative pattern recognizer. A device that automatically classifies complex signals derived from any type of information that can be changed into an electrical signal. s c h e d u l e d maintenance-Maintenance performed according to an established plan. scheduling -Determining the order in which job programs will use the available computer facilities. schematic-1. A diagram that shows, by means of graphic symbols, the electrical connections and functions of a specific circuit arrangement. 2. A representation of the components of an electrical circuit and their interconnections by symbols and lines. s c h e m a t i c circuit diagram -See schematic diagram. s c h e m a t i c diagram- Also called a schematic circuit diagram, diagram, or schematic. 1. A diagram of the electrical scheme of a circuit, with components represented by graphical symbols. 2. A drawing that shows by means of graphic symbols the electrical connections, components, and functions of a specific circuit arrangement. 3. A functional diagram of an electrical circuit in which the components arc represented by conventional symbols, and wires interconnecting them by lines. S c h e r i n g bridge- A four-arm alternating-current bridge used for measuring capacitance and dissipation factor. The unknown capacitor and a standard loss-free capacitor form two adjacent arms, the arm adjacent to the standard capacitor consists of a resistor and capacitor in parallel, and the fourth arm is a nonreactive resistor. schlieren -An optical system that produces images in which the illumination or hue at a given point is related to the angular deflection a light ray undergoes in passing through the corresponding point in the object. The object is back-illuminated, and a straightedge, circular aperture, or graded density or multicolored filter is employed in the system to discriminate between deflected and undeflected rays. S c h m i d t antenna-A microwave scanning antenna similar in principle to the optical Schmidt camera. The

spherical reflector has a spheric microwave lens at the center of curvature and a scanner is located approximately halfway between these elements. S c h m i d t optical system- An optical system for magnifying and projecting a small, brilliant image from a projection-type cathode-ray tube onto a screen. S c h m i t t limiter-See Schmitt trigger. S c h m i t t trigger-Also called Schmitt limiter. 1. A bistable pulse generator in which an output pulse of constant amplitude exists only as long as the input voltage exceeds a certain dc value. The circuit can convert a slowly changing input waveform to an output waveform with sharp transitions. Normally, there is hysteresis between an upper and a lower triggering level. 2. A regenerative circuit that changes state abruptly when the input signal crosses specified dc triggering levels. 3. A bistable device that utilizes the effect of hysteresis. In the Schmitt trigger, hysteresis is a form of nonlinear operation that forces the output to be dependent not only on the absolute value of the input, but also on the most recent prior value of the input. This hysteresis is characterized by two different switching theshold levels: one for positivegoing input transitions and the other for negative-going input transitions.

+ "cc

6 -VEE

Schmitt trigger.

schmoo plot-An x , y plot giving the padfail region for a specific test while varying the parameters in x and y coordinates. s c h o o p i n g -Spraying metal onto the ends of the roll of a metallized capacitor. This provides a metal surface on the ends of the roll to which the leads arc then soldered. Schottky-A bipolar technology that is faster than standard TTL but often uses more power.

Schottky barrier - scintillation

669 Schottky barrier-- 1. A simple metal-to-semiconductor interface that exhibits a nonlinear impedance. 2. A metal and a semiconductor. A metal-insulatorsemiconductor (MIS) barrier contains a very thin film of oxide between lhe metal and semiconductor Iayers; in a semiconductor-insulator-semiconductor (SIS) barrier, a high-conductivity, transparent, large-bandgap semiconductor layer replaces the metal of the MIS cell. 3. A junction diode with the junction formed between the semiconductor and a metal contact rather than between dissimila semiconductor materials, as in the case of an ordinary pn diode. Schottky-barrier detector-A detector based on a Schotf.ky barrier-a current-rectifying contact at a junction between a semiconductor and a metal. Schottky barrier diode- Also called Schottky diode and hot carrier diode. 1. A junction diode with the junction formed between the semiconductor and a metal contact rather than between dissimilar semiconductor materials, as in the case of an ordinary pn diode. 2. A special diode characterized by nanosecond switching speed, but relatively low voltage (45 V max) and limited temperature range (125T to 150'C). Schottky diode-See Shottky barrier diode. Schottky rectifier- A high-speed rectifier that makes M S of ~ the rectification effect of a metal-to-silicon barrier. Low forward-voltage characteristics provide high rectification efficiency, while majority carrier forward conduction enhances switching speed. Schottky transistor logic -Abbreviated STL. An improved version of integrated injection logic that has a power-delay product that is three times lower than that for 1%. Schottky TTL-1. A TTL circuit that incorporates Schottky diodes to greatly speed up TTL circuit operation. 2. A very high speed TTL circuit using metdsemiconductor diodes (Schottky diodes) to prevent transistors from saturating. 3. Integrated circuits modified by having a special diode built into each transistor. These diodes enable the transistor to be turned off much faster than would otherwise be possible. scierntCfic notation-In a calculator, the number entered or a result displayed in terms of a power of 10.

Schematic. ISOLATION

02

D3

P

EMITTER

BASE

Schottky barrier diode.

For example, the number 1234 is entered as 1.234 x lo3, and the number 0.001234 would appear as 1.234 x scintillate-To emit flashes of light. scintillation- 1. In radio propagation, a random and usually relatively small fluctuation of the received field about its mean value. 2. Also called target glint or wander. On a radar display, a rapid apparent displacement of the target from its mean position. 3. The flash of light produced by an ionic action. 4. A momentary breakdown of a tantalum oxide film in a capacitor, accompanied by rapid heating of the dielectric. Such events are caused by capacitor overvoltages or improper techniques of capacitor manufacture. 5. The flash of light produced by certain crystalline materials when a charged particle is passed through them. 6. Rapid fluctuation in parameters such as the amplitude or the phase of a wave passing though a medium with small-scale irregularities that cause irregular changes in the transmission path with time; akin to twinkling.

'

P

02

Y N - P

OXIDE

7,-P

COLLECTOR

Cross section.

01

01

90,

EN

N + Y

Schottky transistor logic.

03

C

E,

P

Y

P

scintillation conversion efficiency

- scrambled speech

scintillation conversion efficiency-In a scintillator, the ratio of the optical photon energy emitted to the energy of the incident particle or photon of ionizing radiation. scintillation counter -A device that indirectly detects charged particles and gamma rays and neutrons by using a photomultiplier tube to convert the short flashes of light produced as the particle passes through a transparent scintillating material into electric signals that can be recorded. One advantage of scintillation counters is that they are very fast; by this is meant that they have a very small resolving time. scintillation-counter cesium resolution-The scintillation-counter energy resolution for the gamma ray or conversion electron emitted from cesium-137. scintillation-counter energy resolution -In a scintillation counter, a measure of the smallest discernible difference in energy between two particles or photons of ionizing radiation. scintillation-counter energy-resolution constant-The product of the square of the scintillationcounter energy resolution times the specified energy. scintillation-counter h e a d -The combination of scintillators and photosensitive devices that produces electrical signals in response to ionizing radiation. scintillation-counter time discrimination-In a scintillation counter, a measure of the smallest time interval between two successive individually discernible events. Quantitatively, the standard deviation of the timeinterval curve. scintillation crystals- Special crystals that emit flashes of light when struck by alpha particles. scintillation d e c a y time-The time required for the decrease of the rate of emission of optical photons in a scintillation from 90 percent to 10 percent of the maximum value. scintillation duration -The interval from the time of emission of the first optical photon of a scintillation to the time when 90 percent of the optical photons of the scintillation have been emitted. scintillation rise time-The time interval occupied by the increase of the rate of emission of optical photons of a scintillation from 10 percent to 90 percent of the maximum value. scintillator-The combination of the body of scintillator material and its container. scintillator material -A material that exhibits the property of emitting optical photons in response to ionizing radiation. scintillator-material total-conversion

670

scoring s y s t e m -In motion-picture production, a system for recording music in time with the action on the film. Scott connection -A method of connecting transformers to convert two-phase power to three-phase or vice versa. Scott’s b r e a k d o w n theory-Breakdown is due to the attainment of a critical avalanche size that leads to a conducting path. SCR -Abbreviation for silicon controlled rectifier. The formal name is reverse-blocking triode thyristor. 1. A thyristor that can be triggered into conduction in only one direction. Terminals are called anode, cathode, and gate. 2. A semiconductor device that functions as an electrically controlled switch for dc loads. The SCR is one type of thyristor. 3. A power switching device in which a pulse at the gate (input) initiates a switching action in the output circuit. It conducts only during the positive half-cycle of ac. 4. A type of thyristor that is designed for forward bias, unidirectional power switching, and control. See also thyristor.

MOLDED PLASTIC

GATE

WIRES

SILICON CHIP

In molded plastic case.

CURRENT

HEAVY. CONDUCTION REGION

effi-

ciency-In a scintillator material, the ratio of the produced optical photon energy to the energy of a particle or photon of ionizing radiation that is entirely absorbed in the scintillator material. scissor-To apportion a drawing into segments that can be viewed on a CRT screen. scissoring -The ability of the vector generator to blank the beam whenever it is moved outside of the screen (where the image becomes distorted). scope -Slang for a cathode-ray oscilloscope. s c o p h o n y television s y s t e m -A mechanical television projection system developed in England. In it, ingenious optical and mechanical methods provide large, bright images suitable for theater installation as well as home television receivers. The apparent screen brightness is multiplied several hundred times because several hundred picture elements are projected simultaneously. s c o r e d substrate-A substrate that has been scribed with a thin cut at the break lines. See snap-strate.

/

REVERSE BREAKDOWN

Characteristic curve.

SCR. scramble- 1. To transpose andlor invert bands of frequencies, or otherwise modify the form of the intelligence at the transmitting end, according to a prearranged scheme in order to obtain secrecy. 2. To mix, in cryptography, in a random or quasi-random fashion. scrambled s p e e c h -Also called inverted speech. Speech that has been made unintelligible (e.g., for secret transmission) by inverting its frequency. At the receiving end, it can then be converted back into intelligible speech by reinverting the frequency.

67 1 scrambler-1. A device used to electronically alter a signal so that it can only be viewed or heard on a receiver equipped with a special decoder. 2. An electrical device that uses one or more methods to convert speech or video into a secret, unintelligible form. 3. A device that changes data so it appears to be in a random pattern. A descrambling device can change (unscramble) this data back to its original pattern. scrambler circuit-Also called a speech scrambler. A circuit in which essential speech frequencies are divided into several ranges by filters and then inverted to produce scrambled speech. See also speech inverter. scrambling-A method of altering the identity of a video or audio signal in order to prevent its reception by persons not having authorized decoders. scratch filter--A low-pass filter, often an integral part of an amplifier circuit, that attenuates the higher frequency noise derived from disk recordings. The scratch filter is also suitable for the suppression of background noise produced by tape background hiss. scratch pad -1. hiformation that the processing unit of a computer stores or holds temporarily. It is a memory containing subtotals for various unknowns that are needed for final results. 2. An area of RAM used for short-term storage of data during a process. 3. Group of general-purpose registers without specific function, providing a high-speed workspace. Usually, an internal RAM in a computer. scratch-pad memory- 1. A high-speed, limitedcapacity computer information store that interfaces directly with the central processor. It is used to supply the central processor with the data for the immediate computation, thus avoiding the delays that would be encountered by interfacing with the main memory. (The function of the scratch-pad memory is analogous to that of a pad of paper used for jotting down notes.) 2. A highspeed memory used to temporarily store small amounts of data that may be needed often and without delay. 3. Any memory space used for the temporary storage of data. Typically, scratch-pad memories are high-speed integrated circuits that are addressed as internal registers. Screen- 1. The sudace on which the visible pattern is produced in a cathode-ray tube. 2. A metal partition that isolates a device from external electric or magnetic fields. 3. See screen grid. 4. Surface on which the master artwork of the circuit pattern is projected. Screen fabrics include polyester, stainless steel, nylon, and silk. 5 . The surface of a medium on which a visible image, pattern, or picture is produced, generally within a camera or cathoderay tube. screen angle-A vertical angle bounded by a straight line from the radar antenna to the horizon and the horizontal at the antenna, assuming a 413 earth's radius. Screen deposition-The laydown of a circuit pattern on a substrate using the silk screening technique. Screen dissipation-The power that the screen grid dissipates as heat after bombardment by the electron Strealtl.

screen grid-Also called a screen. A grid placed between a control grid and an anode in a vacuum tube and usually maintained at a fixed positive potential. By reducing the electrostatic influence of the anode, it prevents the electrons from bunching in the space between the screen grid and the cathode. screen-grid modulation -Modulation produced by introducing the signal into the screen-grid circuit of any multigrid tube where the carrier is present. screen-grid tube-A vacuum tube in which a grid is placed between the control grid and the anode to prevent the latter from reacting with the control grid.

scrambler

- scrolling

screen-grid voltage -The direct-voltage value applied between the screen grid and the cathode of a vacuum tube. screening- 1. The process whereby the desired film circuit patterns and configurations are transferred to the surface of a substrate during manufacture by forcing a material through the open areas of the screen, using the wiping action of a soft squeegee. 2. 'The display of raw or processed data for operator verification. 3. The process of performing 100-percent inspection on product lots and removing defective units. screening test-A test or combination of tests intended to remove unsatisfactory items or those likely to exhibit early failure. screen printing (thickfilm)-- 3. The art of depositing conductive, resistive, and insulating materials on a dielectric base. This deposition is made through selected open areas in screens with inks or pastes forced through the open areas of the screen by squeegee motion onto the substrate base. In some cases, masks instead of conventional mesh screens may be used. 2. The basic thickfilm deposition process in which the paste is squeegeed through a fine-mesh stencil screen to produce a prescribed pattern on a substrate. screen savers -Software that automatically blanks a monitor screen or displays a moving pattern if there has been no user interaction with the computer for a specified time. Screen savers are used to preventing a fixed pattern from being burned into the screen phosphor. As soon as the operator touches any key or moves the mouse, the screen saver disappears and the original display returns to the screen. scribe and break-ne procedure used to separate a processed semiconductor wafer into individual ICs. Nmow channels between individual ICs are mechanically weakened by scratching with a diamond tip (scribe), sawing with a diamond blade, or burning with a laser. The wafer is mechanically stressed and broken apart along the channels (called scribe lines), thereby separating the individual ICs (dice). scribe projection--A method of automatic information presentation in which information is placed on a small metallic-coated glass slide by using a movable, servocontrolled, fine-pointed scribe to remove the coating. Light passed through the scribed area is projected onto a screen. scribing- 1. A process, similar to glass cutting, in which a slice of semiconductor devices is scored in rows and columns so that it may be separated easily into individual devices. The process is performed in a machine called a scriber by repeated movement of a weighted diamond stylus across the slice to form the scored pattern. 2. Scratching a tooled line or laser path on a brittle substrate to allow a wafer to be cleft or broken along the line, producing IC, transistor, or diode chips when all breaks are completed. scribing machines and tods-Equipment used to separate wafers into individual devices, chips, or dice. This has been done by crude techniques similar to glass cutting, but is now accomplished by more efficient methods using truncated pyramid diamond scribers, automated machines, conical tools, or lasers. script-Much like a macro, a set of program commands used to automate routine computing tasks. scroll -1. To move a video display up or down, line by line, or side to side, character by character. 2. To move all or part of the screen material up or down, or left or right, to allow new information to appear. scrolling -1. Moving the contents of the screen of a CRT up or down by one line at a time. 2. A multiplerung display function that allows all displayed rungs to be

s c r u b b i n g action

- secondary cell

moved up or down, adding the next or preceding rung at the bottom (or top) of the display. (As determined by the user, the display may be changed either one rung at a time or continuously.) 3. The vertical movement of information on a CRT screen, caused by the dropping of one line of displayed information for each new line added; the movement appears as an upward rolling if the new line is added at the bottom of the screen, and vice versa. scrubbing action-Rubbing of a chip device around on a bonding operation to break up the oxide layer and improve wetability of the eutectic alloy used in forming the bond. SCS-Abbreviation for silicon-controlled switch. SCU-Abbrevitaion for subscriber channel unit. A telephone interface circuit. S-curve-An S-shaped frequency-response curve showing how the output of a frequency-modulation detector or circuit varies with frequency. SDLC-Abbreviation for Synchronous Data Link Control. 1. A communications line discipline that initiates, controls, checks, and terminates information exchanges or communications lines. SDLC is designed for full-duplex operation (simultaneously sending and receiving data). 2. A protocol specifying a layered approach to serial data communications. sea clutter-See sea return. seal-Any device used to prevent gases or liquids from passing through. sealed contacts-A contact assembly enclosed in a sealed compartment separate from the other parts of the relay. s e a l e d - g a g e pressure transducer -A pressure transducer that has the sensing element sealed in its case at room ambient pressure. The sealing method holds the original internal pressure for long periods of time. s e a l e d meter-A meter constructed so that moisture or vapor cannot enter the meter under specified test conditions. sealed relay- A relay that has both coil and contacts enclosed in a relatively airtight cover. sealed tube-A hermetically sealed electron tube used chiefly for pool-cathode tubes. sealing compound-A type of wax or pitch compound used in dry batteries, capacitor blocks, transformers, or circuit units to keep out air and moisture. sealing off-The final closing of the bulb of a vacuum tube or lamp after evacuation. seam welding -A resistance welding process in which overlapping spot welds are made progressively along a joint by means of circular electrodes. The circular seam-welding wheels roll along the overlapping edges to be welded, and the control circuit is arranged to pass current at sufficiently close intervals to produce the desired degree of overlapping of the spot welds. The primary purpose of a seam-welding joint is to produce liquid or airtight containers from comparatively thin sheet metal. search-1. In a radar operation, the directing of the lobe (beam of radiated energy) in order to cover a large area. A broad-beam antenna may be used, or a rotating or scanning antenna. 2. A systematic examination of the available information in a specific field of interest. 3. To scan available stored information. 4.The process of applying a sweeping tuning signal to the free-running oscillator portion of a phase-locked oscillator, causing the oscillator output frequency to pass within the capture bandwidth of the feedback network and ensuring a locked condition in response to a new reference frequency. 5. The process of finding a particular item in a file. Search

672 techniques include the sequential or linear search, the binary or logarithmic search, and direct lookup. s e a r c h coil -See magnetic test coil. search engine- 1. A computer program that helps users find information in most databases. 2. A database or index that can be queried to help find information on the World Wide Web. s e a r c h gate-A gate pulse that is made to search back and forth over a certain range. searchlighting -In radar, the opposite of scanning. Instead, the beam is projected continuously at an object. searchlight-type sonar- An echo-ranging system employing the same narrow beam pattern for both transmission and reception. search radar-A radar intended primarily for displaying targets as soon as possible after their entrance into the coverage area. s e a r c h receiver -See intercept receiver. s e a r c h time-The time required for location of a particular data field in a computer storage device. The process involves comparison of each field with a predetermined standard until an identity is obtained. Contrasted with access time. sea return-Also called sea clutter. In radar, the aggregate received echoes reflected from the sea. seasonal factors-Factors that are used to adjust sky-wave absorption data for seasonal variations. Those variations are due primarily to seasonal fluctuations in the heights of the ionospheric layers. seasoning -Overcoming a temporary unsteadiness of a component that may appear when the component is first installed. seating time-The elapsed time after the coil of a relay has been energized until the armature of the relay is seated. sec- Abbreviation for secondary winding of a transformer. SEC-Abbreviation for secondary-electron conduction. The transport of charge by secondary electrons moving through the interparticle spaces of a porous material under the influence of an externally applied electric field. SECAM-Abbreviation for Sequential Color and Memory System (Sdquential Couleur avec it46mire). A color TV system with 625 lines per frame and 50 fields per second, used primarily in France, Russia, parts of Africa, and the former states of the Soviet Union. SECAM uses alternating lines of U, V chroma information to modulate the frequency. It is quite different from NTSC and PAL standards. s e c o n d a r y - 1. The transformer output winding in which the current is due to inductive coupling with another coil called the primary. 2. Low-voltage conductors of a power-distributing system. s e c o n d a r y area -See secondary service area. secondary breakdown -A condition that occurs in bipolar transistors brought on by hot spots occurring within the device structure. This is a type of thermal runaway and in most cases causes permanent device damage. s e c o n d a r y calibration -Also called sense step. Calibration of accessory equipment in which a transducer is deliberately unbalanced electrically to change the output, voltage, current, or impedance. Generally performed by means of a calibration resistor that is placed across one leg of the bridge. s e c o n d a r y cell-A voltaic cell that, after being discharged, may be restored to a charged position by an electric current sent through the cell in a direction opposite that of the discharge current. See also storage cell, 1.

s e c o n d a r y circuit

673 s e c o n d a r y circuit-The high-voltage part of an ignition system. s e c o n d a r y coior--A color produced by combing any two primary colors in equal propodons. In the lightadditive process, the three secondary colors are cyan, magenta, and yellow. S e c o n d a r y C o m m u n i c a t i o n s Authorization See SCA. s e c o n d a r y electron-An electron emitted from a material as a result of bombardment by electrons or of the collision of a charged particle with a surface. secondary-electron conduction tube -A sensitive TV tube that uses a two-step process to convert the invisible image to a charge image. In the image intensifier stage, fight ejects electrons from a photoemitter. After imaging and amplification in the middle or imaging section, the primary photoelectrons fall on the thin-film face of the secondary target. This charge image modulates the scanning beam current from the reading section. The electric field applied across the film causes a majority of the secondary electrons to be transported through a potassium chloride low-density fih layer to produce a secondary conduction current. secondary-electron multiplier -An amplifier tube in which the electron stream is focused onto a succession of targets, each of which adds its secondary electrons to the stream. In this way, considerable amplification is provided. secondary emission -The liberation of electrons from an element other than the cathode as a result of being struck by other high-velocity electrons. In a vacuum tube there are usually more secondary than primary electrons -a desirable phenomenon in electronmultiplier or dynatron-oscillator tubes. However, pentodes have a suppressor grid to nullify the undesirable effect of secondary emission. secondary-emission ratio-The average number of secondary electrons emitted from a surface per incident primary electron. secondary-emission tube-A tube that makes use of secondary emission to achieve a useful end. The photomultiplier is an example. s e c o n d a r y failure-1. A failure occurring as a direct result of the abnormal stress on a component brought about by the failure of another part or parts. 2. Any falure that is the direct or indirect result of a primary failure. secondary grid omission -Emission from the grid OF a tube as a result of high-velocity electrons being driven against it and knocking off additional electrons. The effect is the same as for primary grid emission. secondary insulation -A nonconductive material whose prime functions are to protect the conductor against abrasion and provide a second electrical barrier. Placed over the primary insulation. secondary line-The conductors connected between the secondaries of distribution transformers and the consumer service entrances. s e c o n d a r y radar--See radar. s e c o n d a r y radiation -Random reradiation of electromagnetic waves. secondary service area-Also called the secondary area. The service area of a radio or television broadcast station within which satisfactory reception can be obtained only under favorable conditions. s e c o n d a r y standard -A unit (e.g., length, capacitance, weight) used as a standard of comparison in individual countries or localities, but checked against the one primary standard in existence somewhere in the world. secondary station-Station licensed for a land location other than &e primary station location, i.e., for

- section

use at a subordinate location such as an office, vacation home, etc. secondary storage- Also called auxiliary storage. 1. Storage that is not an integral part of a computer, but which is directly linked to and controlled by it. 2. Devices that are used to store large quantities of data and programs. To be processed, these data and programs must first be loaded into primary storage. secondary voltage -The voltage across the secondary winding of a transformer.

..

-

L -

SECONDARY WINDING

t

SECONDARY VOLTAGE

Secondary voltage.

secondarywinding -Abbreviatedsec. 1. The winding on the output side of a transformer. 2. A transformer winding that receives its energy by electromagnetic induction from a primary winding. secondary X-rays -X-rays given off by an object irradiated with X-rays. Their frequency depends on the material in the object. second breakdown- 1. A condition in which the output impedance of a transistor changes almost instantaneously from a large value to a small limiting value. It may be distinguished from normal transistor operation by the fact that once it occurs, the base no longer controls normal collector characteristics. Second breakdown is associated with imperfections in the device stnxture, usually being more severe in multiple-diffused, highspeed devices. 2. Lateral current instability through a transistor when operating at relatively high voltages and current. It has its greatest effect under dc conditions, but falls off with increasing temperature and frequencies; the breakdown caused is usually permanent. 3. A potentially destructive phenomenon that occurs in all bipolar transistors. This phenomenon may occur when the transistor operates in the active region with a forward-biased emitter-to-basejunction, or with the application of reverse bias during the cutoff mode of transistor operation. second-channel attenuation -Alternate-channel attenuation. See also selectance, 2. s e c o n d - c h a n n e l interference -Also called alternate-channel interference. Interference in which the extraneous power originates from an assigned (authorized) signal two channels away from the desired channel. second detector- Also called a demodulator. In a superheterodyne receiver, the portion that separates the audio component from the modulated intermediate frequency. second generation --In reference to computers, the period during which transistors took the place of vacuum tubes; the period began in the mid-1950s. second-generation computer-A computer in which solid-state components are used. second source- 1. The manufacturer of a device, other than the original manufacturer. 2. A reference to the manufacture by a competitive company of a part that is electrically and mechanically identical to the original part. second-time-around e c h o -An echo received after a time interval greater than the pulse interval. section -1. A four-terminal network that cannot be divided into a cascade of two simpler four-terminal networks. 2. One individual span of a radio relay system;

sectional center - s e i s m o g r a p h the number of sections in a system is one more than the number of repeaters. sectional center-A toll switching point to which are connected a number of primary outlets. sectionalized vertical antenna -A vertical antenna separated into parts by insulators at one or more points along its length. When suitable reactances or driving voltages are placed across the insulated points, the current distribution is modified to give a more desirable radiation pattern in the vertical plane. sectionalizing-Breaking up of a distribution feeder into smaller sections to minimize the extent of power interruption to customers. sector- 1. The smallest recordable unit on a CD. A disc can contain [(75 sectors per second) x (60 seconds per minute) x (number of minutes on disc)] sectors. The amount of data contained in the sector depends on the physical format and mode in which it is recorded; for regular CD-ROM (Mode 1) data, 2048 bytes (2 kilobytes) of data can fit. 2. A segment of a magnetic disk's track, typically occupied by one block of data. 3. The smallest contiguous storage area on a magnetic secondary storage medium. In microprocessor systems with flexible diskette drives as the secondary storage medium, sector size is typically 128 bytes. sectoral horn-A horn with two parallel and two diverging sides.

Sectoral horn.

sector cable-A multiconductor cable in which the cross section of each conductor is essentially a sector of a circle, an ellipse, or some figure intermediate between them. Sector cables are used in order to make possible the use of larger conductors in a cable of given diameter. sector conductor-A stranded conductor whose cross section is approximately the shape of a sector of a circle. A multiconductor insulated cable with sector conductors has a smaller diameter than the corresponding cable with round conductors. sector display- A range-amplitude display used with a radar set. The antenna system rotates continuously, and the screen (of the long-persistence type) is excited only while the beam is within a narrow sector centered on the object. sector scan -A scan in which the antenna oscillates through a selected angle. sector scanning-Modified circular scanning in which only a portion of the plane or flat cone is generated. secular variation-A slow variation in the strength of the earth's magnetic field.

674

secure mode -The condition of an alarm system in which all sensors and control units are ready to respond to an intrusion. secure voice-Voice message that is scrambled or coded, therefore not transmitted in the clear. SED -Abbreviation for spectral energy distribution. S e e b e c k coefficient-The ratio of the open-circuit voltage to the temperature difference between the hot and cold junctions of a circuit exhibiting the Seebeck effect. S e e b e c k coefficient of a couple-For homogeneous conductors, the limit, as the difference in temperature approaches zero, of the quotient of the Seebeck emf divided by the temperature difference between the junctions. By convention, the Seebeck coefficient of a couple is considered positive if, at the cold junction, the first named conductor has a positive potential with respect to the second. It is the algebraic difference between either the relative or absolute Seebeck coefficients of the two conductors. S e e b e c k effect- 1. The production of an electromotive force (emf) in a circuit composed of two dissimilar metals when their two junctions are at different temperatures. The emf is considered to be the resultant of the Peltier and Thomson emfs around the circuit. 2. Characteristic of dissimilar metals in thermoelectric solar cells whereby separate junctions exhibiting distinct temperatures transform incident voltage into a current. Seebeck e m f -Also called thermal emf. The emf produced by the Seebeck effect. seed-A special single crystal from which large single crystals are grown by the Czochralski technique. seed crystal -A crystal used to start the growing of a large semiconductor ingot. s e e k - 1. With reference to a computer, to look for data according to information given with respect to that data. 2. Moving a set of readwrite heads so that one of them is over the desired track. s e e k time-The time needed to position the head of a disk drive over the specified track. segment-1. In a routine, the part short enough to be stored entirely in the internal storage of a computer, yet containing all the coding necessary to call in and jump automatically to other segments. 2. To divide a program into an integral number of parts, each of which performs a part of the total program and is short enough to be completely stored in internal memory. segmental conductor-A round, stranded conductor composed of three or four sectors slightly insulated from one another. This construction has the advantage of lower ac resistance (less skin effect). segmentation-A technique for managing variablesliced areas of memory, termed segments, that contain logical program parts. segmented thermoelectric arm -A thermoelectric arm made up of two or more materials that have different compositions. segmenting -See partitioning. segment table-A table that describes all segments of a task and is used by the operating system for memory allocation, relocation, and paging. seismic mass- The force-summing member for applying acceleration andor gravitational force in an accelerometer. seismic sensor -A sensor, generally buried under the surface of the ground for perimeter protection, that responds to minute vibrations of the earth generated as an intruder walks or drives within its detection range. s e i s m o g r a p h -An instrument for recording the time, direction, and intensity of earthquakes or of earth shocks produced by explosions.

475 seize-To access or connect to a communications circuit while at the same time making it busy to prevent intrusion. selcal- Acronym for selective calling system. This system allows a teleprinter to be remotely controlled by a unique code. selectance- 1. A measure of the drop in response as a resonant device loses its resonance. It is the ratio of the amplitude of response at the resonant frequency to the response at some other specified frequency. 2. Often expressed as adjacent-channel attenuation (ACA) or secondchannel attenuation (SCA). The reciprocal of the ratio of the sensitivity of a receiver tuned to a specified channel to its sensitivity at another channel a specified number of channels away. selected mode--A mode of operation for an encoder selector circuit in which one set of brushes is selected to be read and another inhibited from being read; also a mode of operation for a system controlling several encoder outputs in which the encoder is selected to be read and all others inhibited from being read. selection check-A verification of a computer instrwtion, usually automatic, to ensure that the correct register or device has been chosen. selection ratio-The ratio of the least magnetomotive force used to select a cell or core to the maximum magnetomotive force used that is not intended to select a cell or core. selection sort-A simple sorting algorithm for putting aU the elements in a file in order. selective-The characteristic of responding to a desired frequency to a greater degree than to other frequencies. selective absorption-Absorption of rays of a certain group of frequencnes only. selective calling -I. A means of calling in which code signals are transmitted for the purpose of activating the automatic attention device at the station being called. 2. A type of operation in which the transmitting station can specify which of several stations on a line is to receive a message. selective diffusion -The process in which specified isolated regions in a semiconductor material are doped. The components in a silicon integrated circuit are formed in this way. selective dump-A dump of a selected area of internal computer storage. selective fading-Fading in which the received signal does not have the same variation in strength for all frequencies in the band. Selective fading usually occurs during multipath transmission. selective interference -Interference whose energy is concentrated within narrow frequency hands. selective ringing-An arrangement used on telephone party lines so that only the bell of the called subscriber rings. selective s q u e l c h ---See squelch circuit. selectivity- 1. The characteristic that determines the extent to which the desired signal can be differentiated from disturbances of other frequencies. 2. A tuner’s abirity to discriminate between a wanted signal and an interfering signal on adjacent frequency settings of the tuning dial. It is the ratio (in decibels) of the signal strength that produces a standard output on the desired channel to the strength of a signal on a nearby channel needed to produce an output 30 dB below the standard level. Selectivity measurements usually refer to signals on the alternate channel (400 kHz from the desired channels in FM and 20 kHz in AM); selectivity measured on the adjacent channel (200 kHz for FM, 10 kHz for AM)

seize - self-balancing recorder is usually lower. The higher the selectivity, the less interference there will be from signals on nearby channels, which is most important in crowded metropolitan areas. 3. The characteristic that determines the extent to which the desired frequency can be differentiated from other frequencies. selectivity control-The control for making a receiver more selective. select lines-In a core memory array, the wires that pass through magnetic cores and carry the selecting coincident currents. selector pulse-A pulse used to identify one event of a series. selector relay-A relay capable of automatically selecting one or more circuits. selector s w i t c h --A multiposition switch that permits one or more conductors to be connected to any of several other conductors. selectron-A computer-memory tube capable of storing 256 binary digits and permitting very rapid selection and access. selenium-A chemical element with marked photosensitive properties and a resistance that varies inversely with illumination. It is used as a rectifier layer in metallic rectifiers. selenium cell -A photoconductive cell consisting of a layer of selenium on a substrate whose electrical resistance varies with the illumination falling on the cell. (Selenium cells have been largely replaced by photocells of one kind or another.) selenium rectifier-A metallic rectifier in which a thin layer of selenium is deposited on one side of an aluminum plate and a highly conductive metal is coated over it. Electrons flow more freely from the coating to the selenium than in the opposite direction, thereby providing rectification.

Selenium rectijier.

self-adapting --Pertaining to the ability of a system to change its performance characteristics in response to its environment. self-adaptive system-A system that can exhibit the qualities of reorganization andlor learning. self-adjusting communication-See adaptive communication. self-aligned t h i c k oxide-A term used to describe a proprietary low-voltage, self-aligned gate process. self-aligning-gate MOS-Abbreviated SAG MOS. 1. An MOS device in which a polycrystalline silicon layer is substituted for the usual aluminum metal gate. The key feature is a different processing technology in which the gate is automatically aligned. 2. A process in which materials like polycrystalline silicon or refractory metals are used in place of aluminum at the gate. These materials act as a mask and result in the gate being automatically aligned between source and drain regions. self-balancing recorder-A recording device operating on the servomechanism principle.

self-bias - self-quenching oscillator self-bias- Also called automatic bias. The voltage developed by the flow of vacuum-tube current through a resistor in a grid or cathode lead. self-capacitance -See distributed capacitance. self-checking code-In computers, a code in which errors produce forbidden combinations. A single self-checking code produces a forbidden combination if a digit gains or loses a single bit. A double self-checking code produces a forbidden combination if a digit gains or loses either one or two bits, and so forth. self-cleaning contact-See wiping contact. self-complementing code-A machine language in which the code of the complement of a digit is the complement of the code of the digit. self-contained instrument -An instrument that has all the necessary equipment built into the case or made a corporate part thereof. self-demagnetization -The process by which a magnetized sample of magnetic material tends to demagnetize itself by virtue of the opposing fields created within it by its own magnetization. Self-demagnetization inhibits the successful recording of signal components having short wavelengths or sharp transitions. self-diagnostic -The hardware and firmware within a controller that allows it to continuously monitor its own status and indicate any fault that could occur within it. self-discharge-The loss of useful capacity of a cell or battery in storage due to internal chemical reactions; for example, chemicals evaporating, or electrolyte slowly reacting with the anode even on open circuit. self-energizing -A type of electrostatic phone that uses the stepped-up signal voltage to supply the dc polarizing voltage required for operation. self-erasure -The tendency for strongly magnetized areas of the tape coating to erase adjacent areas of opposite-polarity magnetization. This is a major cause of loss of high frequencies at reduced tape speeds. self-excitation -The supplying of required exciting voltages by a device itself rather than from an external source. self-excited -A type of generator that provides the current for its own field coils. self-excited oscillator-An oscillator that operates without external excitation and solely by the direct voltages applied to the electrodes. It depends on its resonant circuits for frequency determination (i.e., not crystal controlled). self-extinguishing -Material that ignites and bums when exposed to flame or elevated temperature, but which stops burning when the flame or high temperature is removed. self-focused picture tube- A television picture tube with an automatic electrostatic focus designed into the electron gun. self-generating transducer -A transducer that requires no external electrical excitation to provide an output. self-healing - 1. The characteristic of metallized capacitors by which faults or shorts occurring during operation are removed, or healed, by an internal clearing action, and the part continues to function. See also clearing, 1. 2. The process by which the electrical properties of the capacitor, after local breakdown of the dielectric, are instantaneously and essentially restored to the values before the breakdown. self-healing capacitor-A capacitor that restores itself to operation after a breakdown caused by excessive voltage. The electrode layer is so thin that a small part of the energy released in a breakdown condition is quite sufficient to evaporate the metal layer around the

676 breakdown point and, thus, to terminate the breakdown in the shortest possible time. Only a small healed area is produced in the dielectric, and the capacitor voltage only drops to a minimal extent during the breakdown. self-heated thermistor -A thermistor whose body temperature is significantly higher than the temperature of its ambient medium as a result of the power being dissipated in it. self-heating coefficient of resistivity-The maximum change in resistance due to temperature change caused by power dissipation, at constant ambient temperature. Usually expressed in percent or per-unit (ppm) change in nominal resistance per watt of dissipation. This parameter is actually the product of the power coefficient and the resistor temperature coefficient. self-impedance-At any pair of terminals of a network, the ratio of an applied potential difference to the resultant current at these terminals (all other terminals open). self-inductance- 1. The property that determines the amount of electromotive force induced in a circuit whenever the current changes in the circuit. 2. At any pair of terminals of a network, the ratio of an applied potential difference to the resultant current at these terminals, all other terminals being open. self-induction -The property that causes a counterelectromotive force to be produced in a conductor when the magnetic field produced by the conductor collapses or expands with a change in current. self-inductor- An inductor used for changing the self-inductance of a circuit. self-instructed carry- A system of executing the carry process in a computer by allowing information to propagate to succeeding places as soon as it is generated, without receipt of a specific signal. self-latching relay-A relay in which the armature remains mechanically locked in the energized position until deliberately reset. self-optimizing communication -See adaptive communication. self-organizing -Having to do with the ability of a system to arrange its own internal structure. self-organizing machines-Machines that can recognize, or learn to recognize, such stimuli as patterns, characters, and sound, and which can then adapt to a changing environment. self-passivating glaze-The glassy material in a thick-film resistor that comes to the surface and seals the surface against moisture. self-powered -Equipment containing its own power supply. It may be either a combination of wet and dry cells, or dry cells in conjunction with a spring-driven motor. self -pulse modulation -Modulation accomplished by using an internally generated pulse. See also blocking oscillator, 1. self-pulsing -A special type of grid-pulsing circuit that automatically stops and starts the oscillations at the pulsing rate. self-quenched counter tube-A radiationcounter tube in which reignition of the discharge is inhibited. s e l f - q u e n c h e d detector-A superregenerative detector in which the grid-leak grid-capacitor time constant is sufficiently large to cause intermittent oscillation above audio frequencies. As a result, normal regeneration is stopped just before it spills over into a squealing condition. self-quenching oscillator- An intermittent selfoscillator producing a series of short trains of rf oscillations separated by intervals of quiescence. The quiescence

677 is caused by rectified oscillatory currents, which build up to the point at which they cut off the oscillations. self-rectifying X-ray tube- An X-ray tube operating with an alternating anode potential. self-refresh -In a dynamic RAM, a method of asynchronously refreshing during a battery backup mode of operation with only one control pin held active. self-regulation -The tendency of a component or system io resist change in its condition or state of operation. self-repeating timer-A form of he-delay circuit in which relay contacts are used to restart the tirne delay. self-reset- Automatically r e w i n g to fie original position when normal conditions are resumed (applied chiefly to relays and circuit breakers). self-saturating rectifier-A half-wave rectifyingcircuit element connected in series with the output reactor in a self-smmting windings of a magnetic-amplifier circuit. self-saturation-The saturation obtained in a magnetic amplifier by rectifying the output current of a saturable reactor. self-screening range-The range at which a target can be detected by a radar in the midst of its jamming mask, with a certain specified probability. method of self-selecting v Scan-The vpScan redng a po~ystrop~c cde (primarily the binary code), in which diode logic circuits are used internally in the encoder to perform &e necessary bit-to-bit selection to prevent ambiguity in the encoder output data. syns y n c h r o n o u s m0tor-A chronous motor provided with the equivalent of a squirrelcage winding so it can be started like an induction motor. counter self-stopping modulo-n counter-A having IZ distinct states that stops when it reaches a predetermined maximum number; it then does not accept count pulses until it is reset to a number less than the maximum number. self-,sustained oscillations-OscilIations maintained by the energy fed back frorn the output the input circuit. Self-testing-The ability of a piece of equipment to automaticd'y verify the Propr OFration Of its components or subsystems. se''-threading ree'-A device for and storing tape; in Particular, one that does not require aid affix Or start the first turn Of tape On its winding surface or hub. Flanges on such reels can be continuous and free O f windows; winding Surfaces are continuous and free of distortion-producing threading Slots. self-wiping contacU-See wiping contact. s e l s y n -Electrical remote-indicating instrument operating on direct current in which the angular position of the transmitter shaft carrying a contact arm moving on a resistance strip controls the pointer on the indicator dial. SEN! - 1. Abbreviation for standard electronic module. A subassembly configuration format that meets a particular US.Navy set of specifications. 2. Abbreviation for scanning electron microscope. semantics -The relationships between symbols and their meanings. semaphore-See lock byte. semiacthe homing guidance-A system of homing guidance in which radiations used by the receiver in the nnissile are reflected from a target being illuminated by an outside source. semiactive repeater -A communications satellite that uses a minimum of onboard electronics to take a modulated signal beamed at it from a ground station and

self-rectifying X-ray tube - semiconductor device transfer its information (modulation) into an unmodulated beam (on a different frequency) set up by the receiving station. For this transfer it uses Van Atta or other directive arrays and nonlinear elements. Semiautomatic Ground Environment -Abbreviated SAGE. An air-defense system in which data from air surveillance is processed for transmission to computers at direction centers. semiautomatic keying circuits-Mechanization that provides torn-tape switching systems in teleprinter links. Incoming and outgoing messages are placed on tapes that are inserted m m d Y into a distrhtor that provides automatic mechanical keying of the circuit. f%?miautomatic message switching CentW-A center at which messages axe routed by an operator on the basis Of information contained in them. s e m i a u b l l l a t i cph0nograph-A PhonoWPhhaving automatic arm return and motor shutoff at the end of a record, but no automatic start and tonearm setdown at the beginning Of play. semiautomatic starter-A starter in which some of the operations are not automatic, but selected portions are s e m i a u t o m a t i c tape relay-A method of communication whereby messages are received and retransmitted in teletypewriter tape form involving manual intervention in the transfer of the tape from the receiving reperforator transmitter. to the semiautomatictelephone '#em-' system in which operators receive orders from the calling parties verbally, but use automatic apparatus in making connections' semiconducting material-A solid or liquid having a resistivity midway between that of an insulator and a metal, semiconductor-^, A class of materials, such as silicon and whose electrical properties lie between those of conductors (such as copper and aluminum) and insulators (such as glass and rubber), in which the charge carrierconcentration increases with increasing temperature over some temperature range. Over most of the practical temperature range, the resistance has a negative coefficient. negative semicondncto~possess two types of electrons and positive holes. The charge carriers are usually electrons, but there may be also some ionic conductivity, 2. An electronic device whose main functioning parts are made from semiconductor materials. Examples include lead lead teuwride. selenium, silicon, silicon carbide. Used in &odes, photocells, thermistors. and transistors. 3, A device (or with an electrical conductivity that lies between metal conductors and insulator devices. 4. A material whose resistivity is between that of insulators and conductors. The resistivity is often changed by light, heat, and electric field, or a magnetic field. Current is often achieved by transfer of positive holes as well as by movement of electrons. 5. A material that exhibits relatively high resistance in a pure state and much lower resistance when it contains small amounts of certain impurities. The term is also used to denote electronic devices made from semiconductor materials. semiconductor carrier -A permanent protective structure that provides for mounting and for electrical continuity in application of a semiconductor chip to a major substrate. semiconductor c h i p -A single piece of semiconductor material of any dimension. semiconductor device- 1. A device in which the characteristic distinguishing electron conduction takes place within a semiconductor material, ranging from the

semiconductor diode

- sender

single-unit transistor to multiple-unit devices such as the semiconductor rectifier. Other devices are diodes, photocells, thermistors, and thyristors. 2. A device in which n-type and p-type materials are used in combination to obtain specific characteristics for controlling the flow of current. 3. A device, including its encapsulation and terminals, whose essential characteristics are governed by the flow of charge carriers within a semiconductor material. semiconductor diode-1. A device consisting of n-type and p-type semiconductor material joined together to form a pn junction, which passes current in the forward direction (from anode to cathode) and blocks current in the reverse direction. High reverse voltages, such as transients greater than a specified limit, can destroy the junction due to excessive reverse leakage currents. See also crystal diode. 2. A light-emitting diode that emits coherent light by suitably arranged geometry. Gallium arsenide is used for lasers of this type. 3. A two-electrode semiconductor device that conducts current more easily in one direction. semiconductor-diode parametric amplifier A parametric amplifier using one or more varactors. semiconductor ignition system-An ignition system for internal combustion engines that employs solid-state semiconductors for switching purposes. semiconductor integrated circuit -Abbreviated SIC. 1. Complex circuits fabricated by suitable and selectively modifying areas on and within a wafer of semiconductor material to yield patterns of interconnected passive as well as active elements. The circuit may be assembled h m several chips and use thin-film elements or even discrete components to achieve a specified performance when the necessary device parameters cannot be achieved by materials modification. 2. The physical realization of a number of electric elements inseparably associated on or within a continuous body of semiconductor material to perform the function of a circuit. semiconductor intrinsic properties-Properties of a semiconductor that are characteristic of the ideal crystal. semiconductorjunction -The region of transition between semiconducting regions of different electrical properties, usually between p-type and n-type materials. semiconductor laser- 1. A device in which laser action takes place through stimulated recombination of free electrons in the conduction band with holes in the valence band of a direct-gap semiconductor such as gallium arsenide. 2. A light-emitting diode that uses stimulated emission to produce a coherent-light output. See also diode laser. semiconductor lead wire-Fine wire used to connect semiconductor chips to substrate patterns, packages, other chips, etc. Usually made from an aluminum alloy or gold. semiconductor material-1. A material in which the conductivity ranges between that of a conductor and an insulator. The electrical characteristics of semiconductor materials such as silicon are dependent on the small amounts of added impurities, or dopants. 2. A chemical element, such as silicon or germanium, that has a crystal lattice whose atomic bonds are such that the crystal can be made to conduct an electric current by means of free electrons or holes. semiconductor memory- 1. A memory whose storage medium is a semiconductor circuit. Often used for high-speed buffer memories and for read-only memories. 2. A memory in which semiconductors are used as the storage elements; characterized by low-to-moderate cost storage and a wide range of memory operating speed,

678 from very fast to relatively slow. Almost all semiconductor memories are volatile. 3. A memory with storage elements formed by integrated semiconductor devices, as opposed to a memory composed of ferrite cores. Semiconductor readwrite memories are characterized by low cost, wide speed ranges, and data volatility. Semiconductor read-only memories are nonvolatile. 4. A computer memory that uses silicon integrated-circuit chips. semiconductor photodiode-A semiconductor diode utilizing the photoelectric effect. semiconductor rectifier diode-A semiconductor diode designed for rectification and including its associated mounting and cooling attachments if integral with it. semicustom IC-An LSI circuit that incorporates either linear or digital components. Semicustom ICs are designed to serve as replacements for small- to mediumscale ICs and are based on the concept of integrating extremely complex functions onto a single IC to fulfill a particular custom function. One semicustom IC may replace anywhere from several to more than 100 individual ICs. The semicustom IC, initially processed up to, but not including, the interconnect level, is adapted to specific requirements with relative ease through patterning of the metal interconnect layer. By connecting the transistors (which may number in the thousands) on a single IC in different ways, various functions, such as flip-flops, gates, adders, and parity control, are created. These blocks are then interconnected to form an entire system function on the chip. semicustom large-scale integrated circuitSee gate array, 3. semicustom logic-Chips whose logic functions can be determined in the final stages of manufacturing, such as PLAs and gate arrays. semidirectional microphone-A microphone whose field response is determined by the angle of incidence in part of the frequency range but is substantially independent of the angle of incidence in the remaining part. semiduplex-In a communications circuit, a method of operation in which one end is duplex and one end simplex. This type of operation is sometimes used in mobile systems, with the base station duplex and the mobile station or stations simplex. A semiduplex system requires two operating frequencies. semimagnetic controller-An electrical controller whose basic functions are not all performed by electromagnets. semimetals -Materials, such as bismuth, antimony, and arsenic, having characteristics that class them between semiconductors and metals. semiremote control-Radio-transmitter control performed near the transmitter by devices connected to but not an integral part of the transmitter. semiselective ringing-An arrangement in which the bells of two stations on a telephone party line are rung simultaneously; differentiation is made by the number of rings. semitone-Also called half step. The interval between two sounds. Its basic frequency ratio is equal to approximately the twelfth root of 2. semitransparent photocathode-A photocathode in which radiant flux incident on one side produces photoelectric emission from the opposite side. sender-That part of an automatic-switching telephone system that receives pulses originated by a dial or other source and, in accordance with the pulses received, controls the further operations necessary to establish the connection.

679

sending-end impedance -Also calledthe drivingpoint impedance. The ratio of an applied potential difference of a transmission line to the resultant current at the point where the potential ,differenceis applied. sending filter-A filter used at the transmitting terminal to restrict the transmitted frequency band. sensation level -See level above threshold. sense- 1. In navigation, the relationship between the change in indication of a radionavigational facility and the change in the navigational parameter being indicated. 2. In some navigational equipment, the property of permitting the resolution of 180" ambiguities. 3. To examine or determine the status of some system components. 4. To read holes in punched tape or cards. sense amplifier-1. A circuit used to sense lowlevel voltages such as those produced by magnetic or plated-wire memories and to amplify these signals to the logic voltage levels of the system. 2. A circuit used in communications-electronics equipment to determine a change of phase or voltage and to provide an automatic control function. sense finder-In a direction finder, that portion which permits determination of direction without 180" ambiguity. sense-reversing reflectivity-The characteristic of a reflector that reverses the sense of an incident ray. (For example, a perfect comer reflector is invisible to a circularly polarized radar because it reverses the sense.) sense step-See secondary calibration. sense switch-Qne of a series of switches on the console of the digital computer that permits the operator to control some parts of a program externally. sense wire-A wire threaded through the core of a magnetic memory to detect whether a logical 1 or 0 is stored in the core when the core is interrogated by a read pulse. This technology is no longer in use. nsing -1. The process of determining the sense of an indication. 2. A technique used in a power supply regulator for monitoring the output voltage or current. In local sensing, the monitor points are the output terminals. In remote sensing, the monitor points are located at appropriate locations in the circuit being powered, connected by wire to sensing input terminals on the supply. sensing element-See primary detector. sensing field-The zone in which an object can be sensed by a proximity switch. sensistor -A silicon resistor whose resistance varies with temperature, power, and time. sensitive relay- 1. A relay requiring only a small current. It is used extensively in photoelectric circuits. 2. Any of a number of diEerent types of relays requiring very IOW pickup power. Generally considered to be one requiring less than 100 milliwatts of pickup power. sensitive volume -In a radiation-counter tube, the portion responding to a specific radiation. sensitivity -1. The minimum input signal required in a radio receiver or similar device to produce a specified output signal having a specified signal-to-noise ratio. This signal input may be expressed as power or voltage at a stipulated input network impedance. 2. Ratio of the response of a measuring device to the magnitude of the measured quantity. It may be expressed directly in divisions per volt, milliradians per microampere, etc., or indirectly by stating a property from which sensitivity can be computed (e.g., ohms per volt for a stated deflection). 3. The signal current developed in a camera tube per unit incident radiation density (Le., per watt per unit area). Unless otherwise specified, the radiation is understood to be that of unfiltered incandescent source of 2854 K, and its density, which is generally measured in watts per unit

sending-end impedance

- sensor

area, may then be expressed in lumens per foot. 4. The degree of response of an instrument or control unit to a change in the incoming signal. 5. In tape recording, the relative intensity of the magnetic signal recorded by a magnetizing field of a given intensity. 6. A measurement of the electrical output of a microphone for a given sound pressure level at its diaphragm. 7. The smallest input change that a DMM is able to display. It is equal to the least significant digit on the lowest measurement range. For example, a three-digit DMM with a 100mV range has 100 pV sensitivity. 8. Generally expressed in dBm at a specified impedance (usually 600 ohms), sensitivity is a measure of the lowest DTMF signal level that a receiver can detect. It represents an absolute threshold below which detection of a single frequency is not generated. 9. Measure of the ability of a device or circuit to react to a change in some input. 10. In television, a factor expressing the incident illumination on a specified scene required to produce a specified picture signal at the output terminals of a television camera. 11. A measure of relative output for a given input of a tape, microphone, etc. 12. Characteristic of a receiver that determines the minimum input signal strength required for a given signal output. Sensitivity is usually measured in microvolts (pV). sensitivity a d j u s t m e n t -Also called span adjustment. The control of the ratio of output signal to excitation voltage per unit measurand. Generally accomplished in a system by changing the gain of one or more amplifiers. The practice of placing excitation control components (such as potentiometers or rheostats) in series with the excitation to a transducer is a sensitivity adjustment for the system. However, in the latter case no significant change is introduced in the output-to-input ratio of the transducer. sensitivity control -The control that adjusts the amplification of the radio-frequency amplifier stages and thereby makes the receiver more sensitive. sensitivity-time control-Also called gain-time control or time gain. The portion of a system that varies the amplification of a radio receiver in a predetermined manner. sensitizing (electrostatography) -The establishing of an electrostatic surface charge of uniform density on an insulating medium. sensitometer- An instrument used to measure the sensitivity of light-sensitive materials. sensitometrl(--easurement of the light-response characteristics of photographic film. sensor- 1. In a navigational system, the portion that perceives deviations from a reference and converts them into signals. 2. A component that converts mechanical energy into an electrical signal, either by generating the signal or by controlling an external electrical source. 3. See primary detector. 4. An information-pickup device. 5. A transducer designed to produce an electrical output proportional to some time-varying quantity, as temperature, illumination, pressure, etc. 6. The component of an instrument that converts an input signal into a quantity that is measured by another part of the instrument. 7. Any device that can detect the presence of, or a change in the level of, light, sound, capacitance, magnetic field, etc. 8. A device or component that reacts to a change; the reaction is then used to cause a control or instnunent to function. For example, a thermistor changes resistance as temperature changes, and the resistance changes can be used in an electric circuit to vary current. 9. A transducer that converts a parameter at a test point to a form suitable for measurement by the test equipment. 10. A sensing element. The basic element of a transducer that usually changes some physical parameter to an electrical

sensory robot - sequential interlace signal. 11. A device that is designed to produce a signal or offer indication in response to an event or stimulus within its detection zone. 12. A component that provides an electrical signal in response to a specific physical or chemical stimulus such as heat, pressure, magnetic field, or a particular chemical vapor. Microsensors are fabricated using processes similar to those for manufacturing ICs, or extensions of such processes. Integrated microsensors incorporate an integrated circuit on the same die as that used for the sensor element. sensory robot-A computerized robot with one or more artificial senses, usually sight or touch. sentinel-1. A symbol marking the beginning or end of some piece of information in digital-computer programming. 2. See tag. separate excitation-Excitation in which generator field current is provided by an independent source, or motor field current is provided from a source other than the one connected across the armature. separately instructedcarry--Executing the carry process in a computer by allowing carry information to propagate to succeeding places only when a specific signal is received. separation-The degree to which two stereo signals are kept apart. Stereo realism is dependent on the successful prevention of their mixture before reaching the output terminals of the power amplifier. Tape systems have a separation capability inherently far superior to that of the disc systems. separation circuit-A circuit that separates signals according to their amplitude, frequency, or some other selected characteristic. separation filter-A combination of filters used to separate one band of frequencies from another-often, to separate carrier and voice frequencies for transmission over individual paths. separation loss-The loss that occurs in output when the surface coating of a tape fails to make perfect contact with the surfaces of either the record or reproduce head. separator- 1. An insulating sheet or other device employed in a storage battery to prevent metallic contact between plates of opposite polarity within a cell. 2. An insulator used in the construction of convolutely wound capacitors. 3. See delimiter. septate coaxial cavity-A coaxial cavity with a vane or septum added between the inner and outer conductors. The result is a cavity that acts as if it had a rectangular cross section bent transversely. septate waveguide-A waveguide with one or more septa placed across it to control microwave power transmission. septum-A thin metal vane that has been perforated with an appropriate wave pattern. It is inserted into a waveguide to reflect the wave. Plural: septa. Sequem- 1. The order in which objects or items are arranged. 2. To place in order. 3. A succession of terms so related that each may be derived from one or more of the preceding terms in accordance with some fixed law. sequence checking routine -A checking routine that examines every instruction executed and prints certain data concerning this check. Sequence control-Automatic control of a series of operations in a predetermined order. sequencer- 1. The component of a processor that controls the program flow by implementing branches for subroutine processing and handling interrupts. 2. A device or computer program that records, edits, and plays back MIDI data much like a word processor for music, such that you can fix wrong notes or lengthen or shorten notes.

680 3. A mechanical or electronic device that may be set to initiate a series of events and to make the events follow in sequence. 4. A circuit that pulls information from the control store memory, based on external conditions. 5 . In a bit-slice system, the module in charge of providing the next microprogram address to the microprogram memory. Essentially a complex multiplexer, but may include stack facilities and a loop counter. sequence relay-A relay that controls two or more sets of contacts in a predeteimined sequence. sequencer register-In a computer, a counter that is pulsed or reset following the execution of an instruction to form the new memory address that locates the next instruction. sequence timer - A succession of time-delay circuits arranged so that completion of the delay in one circuit initiates the delay in the following circuit. sequencing equipment -A special selecting device by means of which messages received from several teletypewriter circuits may be subsequently selected and retransmitted over a smaller number of trunks or circuit. sequency of operation-A detailed written description of the order in which electrical devices and other parts of the equipment should function. sequential access-1. An access mode in which records are retrieved in the same order in which they were written. Each successive access to a file refers to the next record in the file. 2. A term used to describe files such as magnetic tape that must be searched sequentially to find any desired record. 3. Computer access method in which a word is accessed by scanning sequential blocks or records. For example: a tape. 4. Data on storage, such as magnetic tape, that much be searched serially from the beginning to find any desired record. sequential-accessfile-A type of file structure in which data may only be accessed sequentially, one record at a time. Data stored on magnetic tape is an example of a sequential file. sequential-access memory -Abbreviated SAM. 1. A serial-type memory in which words are selected in a fixed order. The addressing circuit steps from word to word in a predetermined order, with the result that the access time for the stored information (words) is variable. 2. A method of information retrieval in which the complete memory is scanned and each word is, in its turn,read out, worked on, then rewritten. sequential circuit-A digital circuit that changes state according to an input signal (normally under clock control); it must be tested with a sequence of signals. sequential color television -A color television system in which the three primary colors are transmitted in succession and reproduced on the receiver screen in the same manner. sequential color transmission --The transmission of television signals that originate from variously colored parts of an image in a particular sequential order. sequential computer-A computer in which events occur in time sequence with little or no simultaneous occurrence or overlap of events. sequential control-Digital-computer operation in which the instructions are set up in sequence and fed to the computer consecutively during the solution of a problem. sequentiaf element-A device having at least one output channel and one or more input channels, all characterized by discrete states, such that the state of each output channel is determined by the previous states of the input channels. sequential interlace-A method of interlacing in which the lines of one field are placed directly under the corresponding lines of the preceding field.

68 1 sequential lobing -.A direction-determining technique utilizing the signals, of overlapping lobes existing at the same time. sequential logic-4. A circuit arrangement in a computer in which the output state is determined by the previous state of the input. See also combinatorial logic. 2. Part of a circuit iin which the output values are a function of the inputs and data stored within the circuit. sequential logic element-A device that has one or more output channels and one or more input channels, all of which have discrete states, such that the state of each output channel depends on the previous states of the input channel. sequential operating connector-A form of connector that has two or more groups of contacts that open and close in a predetermined sequence. For example, a connector that is designated for use with ground connections, power distribution, and signal circuits. Operates in such a way that when the connector is closed, the ground contacts close first, power contacts second, and signal contacts last. This sequence is reversed when the connector is opened. sequential operation-The carrying out of operations one after the other. sequential relay- A. relay that controls two or more sets of contacts in a predetermined sequence. sequential sampling -Sampling inspection in which the decision to accept, reject, or inspect another unit is made following the inspection of each unit. sequential scan--A system of TV scanning in which each line of the raster is scanned sequentially. sequential scanning -In television, rectilinear scanning in which the distance from center to center of successively scanned lines is equal to the nominal h e width. sequential switcher- A device that automatically permits the viewing of pictures from a number of CCTV cameras on one CCTV mionitor in a selected sequence. sequential timer--A timer in which each interval is initiated by the completion of the preceding interval. All intervals may be independently adjusted. sequential with memory-See SECAM. serial! - 1. Pertaining to time-sequential transmission of. storage of, or logical operations on the parts of a word in a computer-the same facilities being used for successive parts. 2. The technique for handling a binary data word that has more than one bit. The bits are acted upon one at a time, analogous to a parade passing a review point. 3. Typically refers to a port on a computer for transmitting one bit at a time. Modems and mice typically connect to a serial port. serial access- 1. Pertaining to transmission of data to or from storage in a sequential or consecutive manner. 2. Pertaining to the process in which information is obtained from or placed into storage with the time required for such operations dependent on the location of the information most recently obtained or placed in storage. See also random access. seriaii adder-A device in which additions are performed in a series of steps: the least significant addition is performed first, and progressively more significant additions are performed in order until the sum of the two numbers is obtained. serial arithmetic unit-In a computer, a unit in which the digits are opeirated on sequentially. See also parallel arithmetic unit. serial bit-Pertaining to computer storage in which the individual bits making up a word appear in time sequence. serial computer- A computer having a single arithmetic and logic unit.

sequential lobing - serial programming serial counter -Also called ripple-though counter. A counter in which each flip-flop cannot change state until after the preceding flip-flop has changed state; relatively long delays after an input pulse is applied to the counter can occur before all flip-flops reach their find states. serial data -Data transmitted sequentially, one bit at a time. serial digital computer-A computer in which the digits are handled serially. Mixed serial and parallel machines are frequently called serial or parallel, according to the way the arithmetic processes are performed. An example of a serial digital computer is one that handles decimal digits serially, although the bits that comprise a digit might be handled either serially or in parallel. See also parallel digital computer. serial interface- 1. A data channel that transfers digital data (1s and Os) in a serial fashion, one bit after another. Serial interfaces save space by requiring fewer lines compared with parallel interfaces, bnt at the sacrifice of data transfer speeds. 2. A port that sends or receives the eight bits in each byte one by one, much like beads on a string. Printers located far from a computer usually require a serial interface. serial 110-A method of data transfer between a computer and a peripheral device in which data is transmitted for input to the computer (or output to the device) bit by bit over a single circuit. serialize -To convert from parallel-by-bit to serialby-bit. serially reusable routine-A computer routine in main storage that can be used by another task following conclusion of the current use. serial memory- 1. A memory in which information is stored in series and reading or writing of information is done in time sequence, as with a shift register. Compared with a RAM, a serial memory has slow to medium speed and lower cost. See sequential-access memory. 2. A memory whose contained data is accessible only in a fixed order, beginning at some prescribed reference point. Data in any particular location is not available until all data ahead of that location has been read. Such a memory is inherently slow compared with a random-access memory. serial mode-A type of computer operation that is performed bit by bit, generally with the least significant bit handled first. Read-in and readout are accomplished bit after bit by shifting the binary data through the register. serial operation-1. In a digital computer, infonnation transfer such that the bits are handled sequentially, rather than simultaneously as they are in parallel operation. Serial operation is slower than parallel operation, but it is accomplished with less complex circuitry. 2. Type of information transfer within a programmable controller whereby the bits are handled sequentially rather than simultaneously, as they are in parallel operation. Serial operation is slower than parallel operation for equivalent clock rate. However, only one channel is required for serial operation. serial-parallel--Having the property of being partially serial and partially parallel. serial port-A method of data communication in which bits of information are sent consecutively through one wire. serial printer-A device that can print characters one at a time across a page. serial processing-The sequential or consecutive execution of more than one process into a single device such as a channel or processing unit. Opposed to pardel processing. serial programming -Programming of a digital computer in such a manner that only one arithmetical or logical operation can be executed at one time.

serial storage - serrated rotor plate serial storage -1. In a computer, storage in which time is one of the coordinates used in the location of any given bit, character, or word. 2. A storage media organization in which data or text is serially recorded one character or text block after another. Text access points are retrieved by serially searching through the medium (usually a magnetic-tape cassette or cartridge). serial transfer-Data transfer in which the characters of an element of information are transferred in sequence over a single path. serial transmission -1. Information transmission in which the characters of a word are transmitted in sequence over a single line. 2. The transmission of a character’s bits one at a time (implies a single transmission pathway). 3. A method of transferring information in which the code elements or pulses are sent sequentially, one after another. 4.Moving data in sequence one at a time, as opposed to parallel transmission. s e r i e s -1. The connecting of components end to end in a circuit, to provide a single path for the current. 2. An indicated sum of a set of terms in a mathematical expression (e.g., in an alternating or arithmetic series). series circuit- 1. A circuit in which resistances or other components are connected end to end so that the same current flows throughout the circuit. 2. A circuit in which the current has only one path to follow. 3. An electric circuit in which all the receptive devices are arranged in succession, as distinguished from a parallel circuit. The same current flows through each part of the circuit.

Series circuit.

series connection -A way of making connections

so as to form a series circuit.

series excitation-The field excitation obtained in

a motor or generator by allowing the armature current to flow through the field winding. series-fed vertical antenna -A vertical antenna that is insulated from ground and energized at the base. series f e e d -The method by which the dc voltage to the plate or grid of a vacuum tube is applied b u g h the same impedance in which the alternating current flows. series field-In a machine, the part of the total magnetic flux due to the series winding. series-gate noise limiter -See noise limiter. series loading-hading in which reactances are inserted in series with the conductors of a transmission circuit. series modulation -Modulation in which the plate circuits of a modulating tube and a modulated amplifier tube are in series with the same plate-voltage supply. series motor -Also called series-wound motor. A motor in which the field and armature circuits are connected in series. In small motors with laminated field frames, the performance will be similar when operated on direct current or alternating current. For this reason, the series motor is kquently called a universal motor. A series motor has a high starting torque, but its speed varies with the load. series operation-The connection of two or more power supplies together to obtain an output voltage of the combination equal to the sum of the individual supplies. A common current passes through all the supplies.

682

series-parallel network-Any network that contains only resistors, inductors, and capacitors and in which successive branches are connected in series and/or in parallel. series-parallels w i t c h -A switch that changes the connections of lamps or other devices from series to parallel or vice versa. series peaking network-See peaking network. series regulator-A device that is placed in series with a source of power and is able to automatically vary its series resistance, thereby controlling the voltage or current output.

LOAD

Series-regulated power supply.

s e r i e s resistance -Any sum of resistances installed in sequential order within one circuit. series resistor-A resistor generally used for adapting an instrument so that it will operate on some designated voltage or voltages. It forms an essential part of the voltage circuit and may be either internal or external to the instrument. series resonance-The condition existing in a circuit when the source of electromotive force is in series with an inductance and capacitance whose reactances cancel each other at the applied frequency, thereby reducing the impedance to minimum. series-resonant circuit -A circuit in which an inductor and capacitor are connected in series and have values such that the inductive reactance of the inductor will be equal to the capacitive reactance of the capacitor at the desired resonant frequency. At resonance, the current through a series-resonant circuit is at maximum. series-shunt network-See ladder network. series T-junction -See E-plane T-junction. series winding-In a motor or generator, a field winding that carries the same current as the armature; i.e., this winding is in series with the armature rather than in parallel with it. Series-wound motors are used in fractional-horsepower ac-dc applications, such as fans and electric mixers. Their other chief use is in heavy-duty dc traction equipment, such as electric locomotives, because of their extremely high starting torque. series wound-Characteristic of a generator or motor whose armature and field windings are connected in series. series-wound motor-A commutator motor with field and armature circuits in series. See also Series motor. serpentine cut-A trim cut in a film resistor that follows a serpentine or wiggly pattern to effectively increase the resistor length and increase resistance. serrated pulse-A vertical synchronizing pulse divided into a number of small pulses, each acting for the duration of half a line in a television system. serrated rotor plate -Also called a slotted or split rotor plate. A rotor plate with radial slots that permit different sections of the plate to be bent inward or outward

683 so that the total capacitance of a variable-capacitor section can be adjusted during alignment. serration- 1. The sawtooth appearance of vertical and new-vertical Lines in a television picture. This is caused by their starting at different points during the horizontal scan. 2. A designed irregular surface used as a reservoir to retain excess infiltrating material and/or multiple points to obtain high-current-density resistance welding or resistance brazing. serrodyne -A frequency translator or frequency converter based on linear sawtooth modulation of phase shift or time delay. One convenient modulable device for serrodyne use is a traveling-wave tube, which provides gain as well as frequency translation. serve -1. With reference to cable construction, a type of separator applied directly over the conductor or conductors. The serve may consist of one or more materials such as paper, cotton, silk, nylon, or rayon. These materials may be applied spirally or laterally. 2. A filament or group of filaments, such as fibers or wires, wound around a central core. server- 1. A computer on a network that serves as a central repository for data and programs and which can be accessed over the network by other computers, called clients. 2. A computer or processor that holds applications, files, or memory shared by users on a network. 3. A computer, or a software package, that provides a specific kind of service to allow client software to run on other computers. The term can refer to a particular piece of software, such as a WWW server, or to the machine on which the software is running. A single server could have several different server software packages running on it, thus providing many different servers to clients on the network. server PG-Microcomputer used by a network as a source of disk drives and information. sewice-1, A function offered by some part of an open system to communicating application processes. 2. The conductors and equipment for delivering energy fr0.m the elecwicity supply system to the wiring system of the premises served. serviceability- Those properties of an equipment design that facilitate service and repair in operation. service area -1. The area within which a navigational aid is of use. 2. The area surrounding a broadcasting station where the signal is strong enough for satisfactory reception at all times (i.e., not subject to objectionable interference or fading). service band-The band of frequencies allocated to a class of radio service. service channel - A band of frequencies, usually including a voice channel, utilized for maintenance and fault indication on a communication system. service circuit- An interconnecting circuit in a switching network that may be connected to lines or trunks as required to perform various functions, such as dial pulse detection and audible ringing. service conductors;-The supply conductors that extend from the street main or from the transformers to the service equipment of the premises served. sewice drop -The overhead service conductors from the last pole or otheir aerial support to and including the splices or taps, if any, connecting to the serviceentrance conductors at the premises served. service entrance -The conductors and equipment used for delivering energy from the utility pole to the premises. seavice life- 1. The period of t h e during which a device is expected to perform in a satisfactory manner. 2. The length of time a primary cell or battery needs to

serration - servomotor reach a specified final electrical condition on a service test that duplicates normal usage. service oscillator -See rf signal generator. service provider- A company that provides Internet access. For end users, this service can be as simple as providing Internet e-mail accounts, access to Usenet news groups, ftp, and web browser access via the service provider’s servers. A service provider can also provide a way for connecting an enterprise’s LAN to the Internet, allowing an enterprise to place their own servers on the Internet. service rating-The maximum voltage or current that a component is designed to carry continuously. service request- 1. The appeal by a process or task for access to a system resource. 2. A notification to a system that one element wants to access a resource. service routine-1. In digital computer programming, a routine designed to assist in the actual operation of the computer. 2. A set of instructions to perform a programmed operation, typically in response to an intempt. service switch-A switch, usually in a box, for disconnecting the line voltage from the circuits it services. service unit --In a microwave system, the equipment or facilities used for maintenance communications and transmission of fault indications. serving -1. Of a cable, wrapping applied around the core before a cable is leaded, or over the lead if the cable is armored. Some common materials are jute, cotton, or duct tape. 2. A wrapping of thread or yarn over a relay coil to protect it from damage. servo -Short for servomotor. A device that contains and delivers power to move a control or controls. servoamplifier-A servo unit in which information from a synchro is amplified to control the speed and direction of the servomotor output. servo control- A technique by which the speed or position of a moving device is forced into conformity with a desired or standard speed or position. For example, the speed of a servo-controlled turntable is established by a precision voltage or frequency standard to which it is compared and automatically adjusted to reduce the difference to a minimum. In a servo-controlled tonearm, a small departure of the cartridge from tangency to the groove is sensed and used to activate a motor drive that moves the tonearm to minimize the error. servo IooP-I~a servoamplifier, the entire closed loop formed by feedback from ~ u t p u tto input. In a position servo, the output position is compared to a command signal at the input. servomechanism-1. An automatic feedback-control system in which one or more of its signals represent mechanical motion. 2. A system in which output is compared to input to control error according to desired relationship, or feedback. 3. A self-contained system (except for inputs) in which the feedback signal is subtracted from a desired value so that the difference is reduced to zero. 4.A control system that provides the following: a command instrument t~ control or program the final process; amplification to strengthen and modify the command signal; work instrumentation to maripulate the controlled process; and feedback provision to initiate corrective action when needed. Since feedback signals go from the controlled process back to the original command station, a servo system is said to operate closed-loop. 5. A device in a closed-cycle system that controls a process based on direct feedback from the process. servomotor-A motor used in a servo system. Its rotation or speed (or both) are controlled by a corrective electric signal that has been amplified and fed into the motor circuit.

servo noise

- setup

servo noise-The hunting of the tracking servomechanism of a radar as a result of backlash and compliance in the gears, shafts, and structures of the mount. servo oscillation-An unstable condition in which the load tends to hunt back and forth about the ordered position. servo system-An automatic control system for maintaining a condition at or near a predetermined value by activation of an element such as a control rod. It compares the required condition (desired value) with the actual condition and adjusts the control element in accordance with the difference (and sometimes the rate of change of the difference). servo techniques-Methods of studying the performance of servomechanisms or other control systems. servovalve-Electrohydraulic flow control. An electrical-input, fluid-control valve capable of continuous control. sesquisideband transmission -A system in which the carrier, one full sideband, and half of the other sideband are transmitted. set- 1. To place a storage device in a prescribed state that is opposite to the reset state. 2. To place a binary cell in the 1 state. 3. A permanent change, attributable to any cause, in a given parameter. 4. See equipment. 5. Pertaining to a flip-flop input used to affect the Q output. Through this input, signals can be entered to change the Q output from 0 to 1. It cannot be used to change Q to 0. Opposite of clear. 6. An input to a binary counter or register that forces all binaries to assume the maximum binary state. 7. To place a binary device into a given logic state, usually the 1 state. set analyzer-A test instrument designed to permit convenient measurement of voltages and currents. set breakpoint-A user debug command that causes the setting of a breakpoint in a specified memory location. At program execution, encountering this breakpoint causes temporary program suspension and a transfer of control to the system debug routine. See breakpoint. set composite-A signaling circuit in which two signaling or telegraph legs may be superimposed on a two-wire interoffice trunk by means of one of the balanced pairs of high-impedance coils connected to each side of the line with an associated capacitor network. set input-An asynchronous input to a flip-flop used to force the Q output to its high state. set noise-Inherent random noise caused in a receiver by thermal currents in resistors and by variations in the emission currents of vacuum tubes. set point-In a feedback control loop, the point that determines the desired value of the quantity being controlled. set pulse-A drive pulse that tends to set a magnetic cell. set-reset flip-flop -A standard flip-flop except that if both the set and reset inputs are a 1 at the same time, the flip-flop will assume a prescribed state. set terminal -The flip-flop input terminal that triggers the circuit from its first state to its second state. setting accuracy-The ability to set a knob, switch, or other adjustment to the desired time delay, speed, light, sound, or other parameter. Normally specified in percent of maximum or at set point. settling time- 1. The time interval, following the initiation of a specified stimulus to a system, required for a specified variable to enter and remain within a specified narrow band centered on the final value of the variable. 2. In an operational amplifier, the interval between the time of application of an ideal step input and the time at which the closed-loop amplifier output enters and remains within a specified band of error, usually symmetrical

684 about the final value. Settling time includes a propagation delay and the time needed for the output to slew to the vicinity of the final value, recover from the overload condition associated with slewing, and settle within the specified error range. 3. In a feedback control system, the time required for an error to be reduced to a specified fraction, usually 2 percent or 5 percent, of its original magnitude. 4.The time required for the output frequency of a voltage- or current-tuned oscillator to change from the initial value to within a specified window around the final value in response to a voltage or current stop on the tuning input port. 5. The period required for a digital multimeter’s input circuits to reach a steady-state condition before analog-to-digital conversion is started. There are actually three settling times to evaluate. They are the settling time required with an input step change when operating in a fixed range, the settling time required with a range change, and the settling time required with a function change, such as a switch in measurement from ac to dc volts. 6. Time necessary for a multiplexer’s output to be within a certain error percentage of the input signal once the channel is selected, or turned on. It may be specified as either the semiconductor switch’s switching time plus analog output settling time, or an analog output settling time alone. 7. The time delay between a change of input-signal value and the resultant change in the output signal. Usually expressed in terms of how long it takes the output to arrive at, and remain within, a certain error band around the final value. Often given for several different magnitudes of input-step change. 8. The time required for an amplifier to approach within a percentage of its final steady state value after the application of a step input. It can be specified as 1 percent, 0.1 percent, or 0.01 percent. 9. The elapsed time after a code transition for DAC output to reach a final value within specified limits, usually f 1/z lsb. 10. The time elapsing between the start of a measurement and the instant that the indicator reaches, and remains within, a certain percentage of the final measured value (typically f l percent).

=

SETTLING TIME TO AEJ OR k A E / E , X 100%

Settling time.

set-top unit -Abbreviated STU. Typically refers to the unit/device that sits on top of a television for current cable TV reception. Also refers to digital set-top units, which accept digital media and sometimes support interactivity. setup- 1. The ratio of the difference between black level and blanking level to the difference between reference white level and blanking level, usually expressed in

trap

- traveling-wave tube

direction of propagation, the wave is considered to have both a longitudinal and a transverse component. trap- 1. A selective circuit that attenuates undesired signals but does not affect the desired ones. See also wave trap. 2. A crystal imperfection that can trap carriers. 3. An unprogrammed conditional jump to a known location, the jump being activated automatically by hardware; the location from which the jump occurs is recorded. 4. A device, usually a switch, installed within a protected area, which serves as secondary protection in the event a perimeter alarm system is successfully penetrated. Examples are a trip-wire switch placed across a likely path for an intruder, a mat switch hidden under a rug, or a magnetic switch mounted on an inner door. 5. A volumetric sensor installed so as to detect an intruder in a likely traveled corridor or pathway within a security area. 6. A CPU-initiated interrupt that is automatically generated when a predetermined condition, such as an illegal instruction, a breakpoint, a specified error, or power failure, is detected. Two vector locations are dedicated for each trap type. The vector locations contain the pc and ps for the trap service routine. 7. A method of catching computer program error when illegal instructions are executed or illegal memory locations are accessed. 8. A frequency-sensitive device that is used to attenuate specific signals that cause interference. TRAPAlT diode -Abbreviation for trapped plasma avalanche transit time diode. 1. A microwave avalanche diode that has either an n+pp+ or a p+nn+ structure. It may be manufactured from either silicon or germanium. When the diode is biased into breakdown, an electron-hole plasma fills the entire p or n region, and the voltage across the diode drops. A large current, induced by the low residual electric field, extracts the plasma from the diode. After the plasma is removed, the current drops and voltage rises. Energy stored in the resonant circuits of an oscillator raises the voltage above breakdown, and the cycle repeats. 2. A semiconductor microwave diode that, when its junction is biased into avalanche, exhibits a negative resistance at frequencies below the transittime frequency range of the diode due to generation and dissipation of trapped electron-hole plasma resulting from the intimate interaction between the diode and a multiresonant microwave cavity. TRAPATT oscillator -See trapped avalanche triggered transit (TRAPATT) oscillator. trapezoidal distortion-Distortion in which a televised picture has the shape of a trapezoid (wide at top or bottom) instead of a rectangle. It is due to the interaction between the vertical- and horizontal-deflection coils (or plates) of the cathode-ray tube. trapezoidal generator- An electronic circuit that produces a trapezoidal voltage wave. trapezoidal pattern-An oscilloscope pattern that indicates the percentage of modulation in an amplitudemodulated system.

Trapezoidal pattern.

800 trapezoidal wave -1. A trapezoidal-shaped waveform. 2. A square wave onto which a sawtooth has been superimposed. It is a voltage wave necessary to give a linear deflection current through the coils of a magnetically deflected cathode-ray tube. trapped avalanche triggered transit (TRAPAlT) oscillator- Oscillator device composed of a semiconducting diode in a coaxial resonating cavity. When the biasing current is applied to the diode, highfrequency waves are emitted into the cavity, where they are reflected back and forth and eventually produce a radio-frequency output. trapped flux-In a material in the superconducting state, magnetic flux linked with a closed superconducting loop. trapped plasma avalanche transit time diode -See TRAPATT diode. trapping-1. The holding of electrons or holes by any of several mechanisms in a crystal, thereby preventing them from moving. 2. In a computer, instructions that cause initiation by the central processing unit of an internal interrupt that transfers control to a subroutine which activates the desired operation of the instruction. Also, the subroutine can be changed, thereby causing the operation on the instruction to be changed. trap wire-A low-voltage wire used at hinge points where severe flexing occurs, usually in burglar alarm systems. It is made with tinsel conductor. traveling detector-A probe mounted on a slider and free to move along a longitudinal slot cut into a waveguide or coaxial transmission line. The traveling detector is connected to auxiliary measuring apparatus and used for examining the relative magnitude of any standing-wave system. traveling plane wave-A plane wave in which each frequency component has an exponential variation of amplitude and a linear variation of phase in the direction of propagation. traveling wave -The resulting wave when the electric variation in a circuit takes the form of translation of energy along a conductor, such energy being always equally divided between current and potential forms. traveling-wave amplifiers-A two-port amplifier in which the input signal excites a space-charge wave at one end of a slab of negative-differential-resistivity bulk material. The wave travels through the material between ohmic contacts that serve as a transmission line. The charge builds as it moves, so the output is a larger version of the input. traveling-wave magnetron-A traveling-wave tube in which the electrons move in crossed static electric and magnetic fields that are substantially normal to the direction of wave propagation. traveling-wavemagnetronoscillations -Oscillations sustained by the interaction between the space-charge cloud of a magnetron and a traveling electromagnetic field with approximately the same phase velocity as the mean velocity of the cloud. traveling-wave parametric amplifier-A parametric amplifier that has a continuous iterated structure incorporating nonlinear reactors and in which the signal, pump, and difference-frequency waves are propagated along the structure. traveling-wave phototube-A traveling-wave tube that has a photocathode and a window that admits a modulated laser beam, which causes the emission of a current-modulated photoelectron beam. This beam is then accelerated by an electron gun and directed into the helical slow-wave structure of the tube. traveling-wave tube -Abbreviated TWT. A tube in which a stream of electrons interacts continuously or

traveling-wave-tube amplifier - triad

801 ELECTRON GUN

INPUT /TRANSDUCER

ATTENUATOR

OUTPUT TRANSDUCER

COLLECTOR

i

ELECTADN BEAM

Traveling-wave tube.

repeatedly with a guided electromagnetic wave moving substantially in synchronism with it, and in such a way tliat there is a net transfer of energy from the stream to the wave. traveling-wave-tube amplifier-A power-amplifying piece of equipment yielding about 30 dB of gain over broad bandwidths. The units are built around certain TWTs in the most commonly used frequency bands, and they have external modulation circuitry incorporated. traveling-wave-tube interaction circuit-An extended electrode arrangement used in a travelingwave tube to propagate an electromagnetic wave in such a manner that the traveling electromagnetic fields are r'ztarded to the point at which they extend into the space occupied by the electron stream. tr box- See transmit-receive switch. -The resonant portion of a tr switch. 1. The higher part in harmonic music or voice; of high or acute pitlch. In music, the frequencies from middle C (261.63 hertz) upward. 2. The upper range of audio frequencies. treble boost-Delibeirate adjustment of the amplitude-frequency response OF a system or component to accentuate the higher audio frequencies. tree -A set of connecti-d branches without meshes. treeing -A progressive type of insulation failure in which branching hollow channels slowly penetrate the insulation at rather low appllied voltages. tree network- See hierarchical network. tremolo- 1. The amplitude modulation of an audio tlone, widely used in musical-instrument amplifiers to create effects that add bo the capability of the instrument itself. It is a musical effect characterized by a subaudio modulation of the musical tone. When amplitude modulation is wed, it is called tremolo; a frequency modulation effect is termed vibrato. 2. A warbling or fluctuating effect, approximately seven times per second, in the tone of an instrument characterized by a variation in intensity rather than pitch. See also vibrato. 3. A regular variation in the amplitude of a sound, generally at a frequency between 0.5 and 20 Hz. IF-- Abbreviation for tuned radio frequency. tri -Abbreviation for triode. triac -Also called bidirectional triode thyristor. 1. A bidirectional rectifier (esse:ntially two SCRs in parallel) that fmctions as an electrically controlled switch for ac loads and having an npnpn structure that can be triggered into either forward or reverse conduction by a pulse applied to its gate ellectrode. A triac will pass an alternating current. 2. A thyristor that can be triggered into conduction in either direction. Teminals are called main terminal 1 and gate. 3. A semiconductor device that functions as an electrically controlled switch for ac loads. The triac is one type of thyristor,

ANODE 2

GATE

ANODE 2

ANODE 1

Construction and connections

1 ANODE 2

ANODE 2

GATE[

IANODE

1

GATE

Symbol.

I

Junctions

"ON" STATE

Characteristic

TriaC.

triad -1. Three radio stations operated as a group for determining the position of aircraft or ships. 2. A group of three dots, one of each color-emitting phosphor, on the screen of a color picture tube. 3. A group of three bits or three pulses, usually in sequence on one wire or simultaneously on three wires. 4. Also called a triplex. A group of three insulated conductors twisted together without (or with) a sheath overall. Usually color-coded

triangulation

- trigger circuit

802

for identification. 5. In a color CRT, one set of red, green, and blue phosphors. triangulation -A method of finding the location of a third point by taking bearings from two fixed points a known distance apart. The third point will be at the intersection of the two bearing lines. triax -A type of shielded conductor that employs a shield and jacket over the primary insulation, plus a second shield and jacket over all. Aside from applications requiring maximum attenuation of radiated signals or minimum pickup of external interference, this cable can also be used to carry two separate signals. triaxial cable-1. A special form of coaxial cable containing three conductors. 2. A three-conductor cable with one conductor in the center, a second circular conductor shield concentric with the first, and a third circular conductor shield insulated from and concentric with the first and second, and a braid or impervious sheath overall. TriaxiaP speaker-Trade name applied to the three-way speakers manufactured by Jensen Sound Laboratories, Division of Pemcor, Inc., consisting of three electrically independent speaker elements mounted on a common (single) speaker frame.

MID-FREOUENCY

LOW-FREOUENCY

HIGH-FREOUENCV

MI0

MID-FREOUENCY’ LOW-FREOUE~CY HORN DIAPHRAGM

HIGH-FR~OUENCY HORN

Triaxiul speaker. tribo--A prefix meaning due to or pertaining to friction. triboelectric -Pertaining to electricity generated by friction. triboelectricity-Electrostatic charges generated due to friction between different materials. triboelectric series- A list of substances arranged so that any of them can become positively electrified when rubbed with one farther down the list, or negatively charged when rubbed with one farther up the list. triboluminescence-Luminescence that arises from friction. Usually occurs in crystalline materials. tributary circuit-A circuit that connects an individual drop, or drops, to a switching center. tributary station -A communications terminal consisting of equipment compatible for the introduction of messages into, or reception from, its associated relay station.

Triboelectric Series Positive Asbestos Rabbit fur Glass Mica Nylon Wool Cat fur Silk Paper Cotton Wood Lucite Sealing wax Amber Polystyrene Polyethylene Rubber balloon Sulfur Celluloid Hard rubber Vinylite Saran Wrap Negative

trickle c h a r g e -1. A continuous charge of a storage battery at a slow rate approximately equal to the internal losses and suitable to maintain the battery in a fully charged condition. 2. A continuous direct current, usually very low, that is applied to a battery to maintain it at peak charge or to recharge it after it has been partially or completely discharged. Usually applied to nickelcadmium (nicad) or wet-cell batteries. trickle charger-A device for charging a storage battery at a low rate continuously, or for several hours at one time. tricolor camera -A television camera designed to separate reflected light into three frequency groups, each corresponding to the light energies of the three primary colors. The camera transforms the intensity variations of each primary into amplitude variations of an electrical signal. tricolor picture tube-A picture tube that reproduces a scene in terms of the three light primaries. tricon-A radionavigational system in which an airborne receiver accepts pulses from a triplet (chain of three stations) in a variable time sequence so that the pulses arrive at the same time even though traveling over paths of various lengths. trigatron -An electronic switch in which breakdown of an auxiliary gap initiates conduction. trigger- 1. To cause, by means of one circuit, action to start in another circuit, which then functions for a certain length of time under its own control. 2. A pulse that starts an action or function; for example, a triggered sweep or delay ramp. 3. A timing pulse used to initiate the transmission of signals through the appropriate circuit signal paths. trigger action-The instantaneous initiation of main current flow by a weak controlling impulse in a device. trigger circuit-1. A circuit with two conditions of stability, with means for passing spontaneously or through application of an external stimulus from one to the other when certain conditions are satisfied. See also flip-flop, 1. 2. A circuit in which an electron tube performs the function of a relay. Impulses applied to the input of the

803 tube produce corresponding impulses in the output circuit, starting a chain of events. trigger countdown --.A process that reduces the repetition rate of' a triggering signal. trigger diode -A symmetrical three-layer avalanche diode used to control SCRs and triacs. It has a symmetrical switching mode and therefore fires whenever the breakover voltage is exceeded in either polarity of applied voltage. triggered blocking oscillator -A blocking oscillator that can be reset to iits starting condition by the application of a trigger voltage. triggered spark gap-A fixed spark gap in which the discharge passes between two electrodes and is struck (started) by an auxiliary electrode called the trigger, to which low-power pulses are applied. triggered sweep -In a cathode-ray oscilloscope, a sweep initiated by a signal pulse. trigger electrode-See starter, 2. trigger flip-flop -See T flip-flop. trigger gap-A gas-discharge device with three electrodes that can be triggered upon command. Two electrodes provide the main conduction path, and the third electrode serves as the trigger. triggering-The starting of circuit action, which then continues for a predetermined time under its own control. triggering signal -The signal from which a trigger is derived. trigger level - 1. In a transponder, the minimum receiver input capable of causing the transmitter to emit a reply. 2. The instantaneous level of a triggering signal ai. which a trigger is to be generated. Also the name of the control that selects the llevel. trigger point-The aimplitude point on the input pulse at which triggering of the sweep of a cathode-ray oscilloscope occurs. trigger pulse-A pulse used for triggering. trigger-pulse steering-In transistors, the routing or directing of trigger signals (usually pulses) through diodes or transistors (called steering diodes or transistors) so that the signals affect only one of several associated circuits. trigger' recognition--.In random-sampling-oscilloscope technique, the process of making a response to a suitably applied trigger, such as the time reference for the time window. trigistor -A bistable pnpn semiconductor component with characteristics comparable to those of a flip-flop or bistable multivibrator. un color picture tube-See tri-color picture tube. trim-To make a fine adjustment in a circuit or a ckcuit element. trim control--On soml- regulated power supplies, a control used to make minor adjustments of output voltage. trimmer capacitor-Also called a trimmer. 1. A small variable capacitor associated with another capacitor and used for fine adjustment of the total capacitance of the combination. 2. A small capacitor, usually adjustable by screwdriver, that is placed in parallel with a larger capacitor and used to tune the high-frequency end of the circuit more precisely. 3. A small adjustable circuit element connected in series or parallel with a circuit element of the same kind such that its adjustment sets the combination of the two to a desired value. trimmer potentiometer-A lead-screw-actuated potentiometer. trimmer resistor-A small rheostat used in place of a fixed resistor to permit adjustment of resistance values in a circuiit during initial calibration of an equipment or when recalibration is required.

trigger countdown

- triode thyristor

v Trimmer capacitor.

trimming - 1. The fine adjustment of capacitance, resistance, or inductance in a circuit. 2. The process of using abrasive or laser technique to accurately remove film material from a substrate to change (increase) the resistance value. Thick films are trimmed using either abrasives or lasers; thin-film resistors are laser trimmed. Automated laser trimming is possible using computercontrolled systems. 3. The process of cutting away a portion of a thick-film resistor in order to raise the nominal resistance value. Resistors can often be trimmed to within 1 percent of a desired value. Cutting is done with an air abrasive tool or with a laser beam. The width of the cut is called the kerf. trimming potentiometer-An electrical mechanical device with three terminals. Two terminals are connected to the ends of a resistive element. and one terminal is connected to a movable conductive contact that slides over the element, thus allowing the input voltage to be divided as a function of the mechanical input. It can hnction as either a voltage divider or rheostat. trim notch-The notch made in a resistor by trimming to obtain the design value. See kerf. trinistor -A three-terminal silicon semiconductor device with characteristics similar to those of a thyratron; used for controlling large amounts of' power. trinoscope-1. Any assembly of three kinescopes producing the red, green, and blue images required for tricolor television optical projection (e.g., for theater TV). 2. A color television viewing system with three kinescopes, three lenses, and three deflection yokes used to form the red, green, and blue images required for a tricolor television projection. triode -A three-electrode electron tube containing an anode, a cathode, and a control electrode (grid). triode amplifier- An amplifier in which only triode tubes are used. triode field-effect transistor -A field-effect transistor having a gate region, a sonrce region, and a drain region. Where no confusion is possible. the term may be abbreviated to field-effect triode. triode-heptode converter-A superheterodyne converter circuit that uses a triode local oscillator and a heptode converter, both contained in one envelope. triode-hexode converter - A superheterodyne converter circuit that uses a triode local oscillator and a hexode converter, both contained in one envelope. triode laser-A gas laser whose light output may be modulated by applying signal voltages to an integral grid. triode-pentode -A dual-purpose vacuum tube containing a triode and a pentode in the same envelope. triode pnpn-type switch -A pnpn-type switch having an anode, cathode, and gate terminal. triode thyristor -A three-electrode thyristor, of which one electrode is the gate. Commonly it has three terminals.

trip coil

- trouble-location problem

trip coil-An electromagnet in which a moving armature trips a circuit breaker or other protective device and thereby opens a circuit under abnormal conditions. trip computer-Digital and push-button dashboard electronic system (Chrysler Corp.) that displays readout of speed, miles, fuel, time, and performs computations involving any of these parameters. trip-free relay -See tripping relay. triple-conversion receiver-A communications receiver in which three different intermediate frequencies are employed to give better adjacent-channel selectivity and greater image-frequency suppression. triple detection -See double superheterodynereception. triple diffused -Pertaining to transistors fabricated within a monolithic substrate by three diffusion steps. triple-play tape -Abbreviated TP tape. Very thin recording tape of which it is possible to wind 3600 ft (1097 m) onto a 7-inch (17.8-cm) spool. This would give 180 minutes of playing time at 3 ips (9.525 c d s ) . triple-stub transformer-A microwave transformer consisting of three stubs placed a quarterwavelength apart on a coaxial line. The stubs are adjusted in length to compensate for impedance mismatch. triplet - 1. Three radionavigational stations operated as a group for the determination of position. 2. The waveform of the output voltage of a delay line when the input pulse has a width approximately equal to the resolution of the delay line. triplex-See triad, 4. triplex cable-A cable made up of three insulated single-conductor cables twisted together with or without a common insulating covering. triplexer-A dual duplexer that permits the use of two receivers simultaneously and independently in a radar system by disconnecting the receivers during the transmitted pulse. triplex s y s t e m -A system for simultaneously sending two messages in one direction and one message in the other direction over a single telegraph circuit. tripod -A three-legged camera support. tripping device -A mechanical or electromagnetic device used for opening (turning off) a circuit breaker or starter, either when certain abnormal electrical conditions occur or when a catch is actuated manually. tripping relay- Also called trip-free relay. A device that functions to trip a circuit breaker, contactor, or equipment, or to permit immediate tripping by other devices, or to prevent immediate reclosure of a circuit interrupter in case it should open automatically even though its closing circuit is maintained closed. trip protection circuit-A protective circuit that electrically interrupts the output when an overload occurs. trip voltage- Also called firing voltage. The voltage at which ionization occurs under any circumstances. trip-wire switch-A switch that is actuated by breaking or moving a wire or cord installed across a floor space. trisistor -A fast-switching semiconductor consisting of an alloyed junction pnp device in which the collector is capable of electron injection into the base. Its characteristics resemble those of a thyratron electron tube, and the switching time is in the nanosecond range. tristate- Also called three-state. 1. Logic systems utilizing three conditions on one line: a definite applied high voltage (logical 1); a definite low voltage (logical 0); and an open circuit or undefined state, permitting another part of the circuit to determine whether the line will be high or low. Usually refers to device outputs or systems using outputs of the tristate type. Useful in a

804 bus-organized system. 2. An output configuration found in several logic families that is capable of assuming three output states: high, low, and high impedance. The feature is useful for interconnecting large numbers of devices on the same wires while allowing only one to control the levels of the lines at a given time. tristate device-A device that has three states: on, off, and electrically disconnected. tristimulus values-The amounts of each of the three primary colors that must be combined to match a sample. tri-tet oscillator-A crystal-controlled, electroncoupled vacuum-tube oscillator that is isolated from the output circuit through use of the screen-grid electrode as the oscillator anode. Used for multiband operation because it generates strong harmonics of the crystal frequency. tritium-A radioactive isotope of hydrogen with an atomic number of 3. TRL -Abbreviation for transistor-resistor logic. Trojan h o r s e - 1. Software that, while performing a useful function, has hidden in it code for a program that performs security-breaching or fraudulent functions. 2. A program or data that seems innocuous when loaded into a system or network but later facilitates an attack by a hacker or a virus. trombone -An adjustable U-shaped coaxial line matching assembly. tropicalization -A chemical treatment developed to combat the fungi that ruin electronic equipment in hot, humid jungle regions. tropo -See tropospheric scatter communication. troposphere-The lower layer of the earth’s atmosphere, extending to about 60,000 feet (18,300 m) at the equator and 30,000 feet (9150 m) at the poles. In this area the temperature generally decreases with altitude, clouds form, and convection is active. tropospheric scatter -The propagation of radio waves by scattering as a result of irregularities or discontinuities in the physical properties of the troposphere. t r o p o s p h e r i c scatter communication -Also called tropo. A method or system of transmitting, within the troposphere, microwaves in the UHF or SHF bands to effect radiocommunication between two points on the earth’s surface separated by moderate distances of from 70 to 600 miles (112 to 965 km). Such a span or hop may be augmented by other spans in tandem to permit end-to-end or through circuits up to many thousands of miles. More specifically, this method of communication is now generally understood to embrace a radio system that permits communication over the distances indicated, with excellent reliability and good information capacity, using relatively high transmitted power, frequency modulation, and highly sensitive receiving apparatus. t r o p o s p h e r i c superrefraction -The phenomenon occumng in the troposphere whereby radio waves are bent sufficiently to be returned to the earth. tropospheric wave-A radio wave that is propagated by reflection from a place of abrupt change in the dielectric constant of its gradient in the troposphere. In some cases, the ground wave may be so altered that new components appear to arise from reflections in regions of rapidly changing dielectric constants; when these components are distinguishable from the other components, they are called tropospheric waves. trouble -Failure of a circuit or element to perform in a standard manner. trouble-location problem- A computer test problem whose incorrect solution supplies information on the location of faulty equipment. It is used after a check problem has shown that a fault exists.

805 t r o u b l e s h o o t -See troubleshooting. troubleshooting -Aka troubleshoot. 1. Locating and diagnosing malfunctions or breakdowns in equipment by means of systematic checking or analysis. 2. The work necessary to discover the cause of trouble; also implies the correction of the trouble by elimination of the cause. trouble unit-A weighting figure applied to indicate the expected performance of a telephone circuit or circuits in a given period of time. tr s w i t c h -See transmit-receive switch. ube-Transmit-receive tube. A gas-filled rf switching tube that permits use of the same antenna for both transmitting and receiving by preventing the transmitted power from damaging the receiver. (Usually, a tr unit consists of a cavity containing a discharge gap that connects the transmitter to the antenna, and a coupling circuit that connects the antenna to the receiver when the discharge gap is not fired, indicating that the transmitting tube is quiescent.) true bearing-A bewing given in relation to geographic north, as opposed to a magnetic bearing. true complement -See radix complement. true course-A course in which the direction of the e line is true rather than magnetic north. credit balance-In a calculator, when the answer is negative, the minius sign automatically appears in the display. true hloming -The following of a course in such a way that the true bearing of an aircraft or other vehicle is held constant. true north -Geographic north. true aihm-The actual value of the practical unit of resistance. It is equal to lo9 absolute electromagnetic units of resistance. true power-The average power consumed by a circuit during one complete cycle of alternating current. true radio bearing -See radio bearing. true random noise--A noise characterized by a noma1 or Gaussian distribution of amplitudes. true value-The value of a physical quantity that would be attributed to an object or physical system if that value could be determined with no error. truncate-1. To drop digits of a number of terms in a series, thereby lessening precision. For example, the value 3.14159265 (n)when truncated to five figures is 3.1415, whereas it could be rounded off to 3.1416. 2. To conclude a computational process according to some rule; for example, to stop the evaluation of a power series at a specified term. 3. The dropping of digits or characters from one end of a data itern, causing loss of precision or information. truncated paraboloid -A paraboloid reflector in which a portion of the top and bottom have been cut away to broaden the main radiated lobe in the vertical plane. truncation-The process of dropping one or more digits at the left or right of a number without changing any of the remaining digits. For example, in most operations the number 3847.39 would become 3847.3 when truncated one place at the right, whereas the same number would become 3847.4 when rounded correspondingly. See also round off. truncation error-The error resulting from the use of only a finite number of terms of an infinite series, or from the approximation of operations in the infinitesimal calculus by operations in the calculus of finite differences. trunk- 1. A single message circuit between two points, both of which are switching centers and/or individual message distribution points. 2. A communications channel between two different offices, or between groups

troubleshoot

- tube

of equipment within the same office. 3. A telephone line or channel between two central offices or switching devices, which is used in providing telephone connections between subscribers. 4. A major link in a communication system, usually between two switching centers. t r u n k circuit-A circuit that connects two switching centers. t r u n k facility-That part of a communication channel connecting two or more leg facilities to a central or satellite station. t r u n k group-Those trunks connecting two points, both of which are switching centers and/or individual message distribution points and which make use of the same multiplex terminal equipments. t r u n k hunting-A method by which an incoming call is switched to the next consecutive number if the first called number is busy. t r u n k loss-That part of the repetition equivalent assignable to the trunk used in the telephone connection. truth table- 1. A tabulation that shows the relation of all output logic levels of a digital circuit to all possible combinations of input logic levels in such a way as to characterize the circuit functions completely. 2. A matrix that describes a logic function by listing all possible combinations of inputs and by indicating the outputs for each combination. TSC -Abbreviation for transmitter start code. TSS -Abbreviation for time-sharing system. A computer operating system in which the processor's time is shared among simultaneous users, resulting in an interactive facility. TTL or T2L-Abbreviation for transistor-transistor logic. A bipolar technology used for producing logic gates. Positioned in the evolution of logic families after RTL (resistor-transistor logic) and DTL (diode-transistor logic) and before ECL (emitter-coupled logic) and CMOS. See gate. TTL or T2L compatible-The ability of a device or circuit to be connected directly to the input or output of TTL logic devices. Such compatibility eliminates the need for interfacing circuitry. TTL-compatible circuits -Circuits that meet the input/output interface standards of transistor-transistor logic (TTL) circuits. These can be TTL circuits themselves, or circuits made with other technologies that conform to TTL standards. TTY -An abbreviation of Teletype or teletypewriter unit. TU -See terminal unit. tuba-A powerful land-based radar jamming transmitter operated between 480 and 500 MHz. It was developed during World War II for use against night fighter planes. tube-A hermetically sealed glass or metal envelope in which conduction of electrons takes place through a vacuum or gas. tube bridge- An instrument used in the precise measurement of vacuum-tube characteristics. It contains one or more bridge-type measuring circuits, plus power supplies and signal sources for a14 possible electrode combinations. tube coefficients- Constants that describe the characteristics of a thermionic vacuum tube (e.g., amplification factor, mutual conductance, ac plate resistance). tube complement-The number and types of electron tubes required in an electronic equipment. tube count -A terminated discharge produced by an ionizing event in a radiation-counter tube. tube drop-The voltage measured across a tube, from plate to cathode, when the tube is conducting at its normal current rating.

tube electrometer - tuned resonating cavity tube electrometer-A thermionic vacuum tube adapted for use as an electrometer to measure potential difference. tube heating time-The time required for the coolest portion of a mercury-vapor tube to attain its operating temperature. tubing -Extruded nonsupported plastic materials designed as protection and electrical insulation for exposed components of electrical and electronic assemblies; as opposed to a coated, braided, or woven tube, termed sleeving. tube noise-Noise originating in a vacuum tube (e.g., from shot effect, thermal agitation, etc.). tube shield-A metallic enclosure placed over a vacuum tube to prevent external fields from interfering with the function of the tube. tube s o c k e t -A receptacle that provides mechanical support and electrical connection for a vacuum tube. tube tester-A test instrument for indicating the condition of vacuum tubes used in electronic equipment. tube voltage drop-The anode voltage in an electron tube during conduction. tubular capacitor-A paper, ceramic, or electrolytic capacitor shaped like a cylinder; leads or lugs project from one or both ends. tunable-cavity filter-A microwave filter in which tuning can be accomplished by adjustment of one or more screws that project into the cavity or by adjustment of the positions of one or more rectangular or circular irises in the cavity or waveguide. tunable e c h o box-An echo box consisting of an adjustable cavity operating in a single mode. When the echo box is calibrated, the setting of the plunger at resonance will indicate the wavelength. t u n a b l e magnetron-A magnetron that can be tuned mechanically or electronically over a limited band of frequencies. tuned- Adjusted to resonate or operate at a specified frequency. tuned amplifier-An amplifier in which the load is a tuned circuit. Thus, the load impedance and amplifier gain vary with the frequency. tuned-anode oscillator-See tuned-plate oscillator. tuned antenna- An antenna designed, by means of its own inductance and capacitance, to provide resonance at the desired operating frequency. tuned-base oscillator -A transistor oscillator comparable to a tuned-grid electron-tube oscillator. The frequency-determining device (resonant circuit) is located in the base circuit. tuned circuit -1. A circuit consisting of inductance and capacitance that can be adjusted for resonance at the desired frequency. 2. A circuit that is adjusted to be resonant at a particular frequency. tuned-collector oscillator- A transistor oscillator comparable to the tuned-plate electron-tube oscillator. The frequency-determining device is located in the collector circus. tuned dipole-A dipole antenna that resonates at its operating frequency. t u n e d filter-A resonant arrangement of electronic components that either attenuates signals at a particular frequency and passes signals at other frequencies, or vice versa. tuned-filter oscillator- An oscillator in which a tuned filter is used. tuned-grid oscillator- An oscillator whose frequency is determined by a parallel-tuned tank in the grid circuit. The tank is coupled to the plate to provide the required feedback.

806

tuned-grid, tuned-anode oscillator- See tunedgrid, tuned-plate oscillator. tuned-grid, tuned-plate oscillator -Also called tuned-grid, tuned-anode oscillator. An oscillator having parallel-resonant circuits in both the plate and the grid circuits. The necessary feedback is provided by the plateto-grid interelectrode capacitance.

TANK GRID

m GF + +-

PLATE TANK

6

B

+

Tuned-grid, tuned-plate oscillator.

tuned-plate oscillator- Also called tuned-anode oscillator. An oscillator whose frequency is determined by a parallel-tuned tank in the plate circuit. The tank is coupled to the grid to provide the required feedback. tuned radio-frequency amplifier- Abbreviated TRF amplifier. A tuned amplifier using resonant-circuit coupling and designed to operate at radio frequencies.

2tcned radio-ji-equency amplijier.

tuned radio-frequency receiver -Abbreviated TRF receiver. A radio receiver consisting of several amplifier stages that are tuned to resonate at the carrier frequency of the desired signal by a ganged variabletuning capacitor. The amplified signals at the original carrier frequency are fed directly into the detector for demodulation. The resultant audio-frequency signals are again amplified, and are then reproduced by a speaker. tuned radio-frequency transformer-Abbreviated TRF transformer. A transformer used for selective coupling in radio-frequency stages. tuned-reed f r e q u e n c y meter -A vibrating-reed instrument for measuring the frequency of an alternating current. tuned relay-A relay having mechanical or other resonating arrangements that limit the response to currents at one particular frequency. tuned resonating cavity-A resonating cavity half a wavelength long, or some multiple of a half wavelength, used in connection with a waveguide to produce a resultant wave with the amplitude in the cavity greatly exceeding that of the wave in the guide. For reception of waves, a detecting grating can be placed at the point of maximum amplitude in the cavity to

807 convert the energy to a form suitable for amplification in a telephone or televisioln circuit. A tuned cavity is a nonreflecting termination for a guide. tuned rope -Long lengths of chaff cut to the various lengths necessary for tunin.g to different wavelengths. tuned transformer-- A transformer whose associated circuit elements are adjusted as a whole to be resonant at the frequency of the alternating current supplied to the primary, thereby causing the secondary voltage to build up to higher values than would otherwise be obtained. tuner-In the broad sense, a device for tuning. Specifically, in radio-receiver practice: 1. A packaged unit capable of producing only the first portion of the functions 'of a receiver and delivering either rf, IF, or demodulated information to some other equipment. 2. That portion 'of a receiver that contains the circuits that are tuned to resonance at the received-signal frequency and those which are tuned to the local-oscillator frequency. 3. A radio or TV receiving circuit; a high-fidelity component containing such circuits. tungar rectifier-A gaseous rectifier containing argon gas. It is employed in battery chargers and lowvoltage power supplies. tungar tube -A phanotron (hot-cathode gas-filled rectifier tube) having a heated filament serving as the cathode and a graphite disc as the anode in a bulb filled with low-pressure argon. Used chiefly in battery chargers. tungsten-A metal used in the manufacture of filaments for vacuum tubes and in making contact points for switches and other parts where sparking may occur. After the tungsten is made ductile by rolling, swaging, and hammering, it is very tough. tungsten filament-. A filament used in incandescent lamps, and in thermionic vacuum tubes and other tubes requiring an incandescent cathode. Smaller tungsten filaments are operated in a vacuum, whereas those for larger lamps are used in an inert gas at about ordinary atmospheric pressure. tungsten lamp -An evacuated bulb containing a tungsten filament that is heated by passing an electric current through it. - 1. The adjustment relating to frequency of a circuit or system to secure optimum performance. Commonily, the adjustment of a circuit or circuits to resonance. 2. Making changes in a program to improve its performance without altering its results. tuninig capacitor-. 1. A variable capacitor for adjusting the natural frequency of an oscillatory or resonant circuit. 2. A variable capacitor that is intended to be mechanically actuated frequently throughout its life. make the circuit responsive to a particular frequency.

tuning core-Normally a molded iron core for permeability tuning, into which an adjusting screw has been cemented or molded. diode-A varactor diode used for rf tuning. des functions such as automatic frequency control and automatic fine tuning. eye-Slang for a cathode-ray tuning indicator. tuninlg fork- A two-pronged hard-steel device that vibrates at a definite natuxal frequency when struck or when set in motion by electromagnetic means. Used in some electronic equipment as an accurately controllable source of signals, because its vibrations can be formed

tuned rope -tunnel readily into audio-frequency signals by means of pickup coils. tuning-fork contact-A U-shaped female contact that resembles a tuning fork. It may be stamped or formed. tuning-fork drive-Control of an oscillator by continuous vibrations of a tuning fork. A high harmonic of the oscillating signal obtained from the fork is selected by filter circuits and is strongly amplified to determine the main oscillator frequency in a transmitter or other equipment. tuning in -Adjusting the tuning controls of a receiver to obtain maximum response to the signals of the station it is desired to receive. tuning indicator-A device that indicates whether or not a receiver is tuned accurately. It is connected to some circuit in which current or voltage is maximum or minimum when the receiver is accurately tuned to give the strongest output signal. tuning meter -A direct-current meter connected to a receiver circuit and used for determining whether the receiver is accurately tuned to a station. tuning probe- An essentially lossless probe of adjustable penetration extending through the wall of a waveguide or cavity resonator. tuning range-The frequency range over which a tuned circuit can be adjusted. tuning screw--A screw or probe inserted into a transmission line (parallel to the E field) to produce susceptance of magnitude and sign that depend on the depth of penetration of the screw. tuning stub-1. A short length of transmission line, usually with the free end shorted, connected to a transmission line to provide impedance matching. 2. A type of inductor element, usually adjustable, connected to a transmission line at intervals to improve the voltage distribution. tuning susceptance -The normalized susceptance of an atr tube in its mount due to its deviation from the desired resonance frequency. tuning wand -See neutralizing tool. tunnel action (in a pn junction)-A process whereby conduction occurs through the potential barrier due to the tunnel effect and in which electrons pass in either direction between the conduction band in the nregion and the valence band in the p-region. (Tunnel action, unlike the diffusion of charge carriers, involves electrons only, and for all practical purposes the transit time is negligible.) tunnel cathode-A metal-insulator-metal sandwich. Electrons tunnel from the metal substrate and appear in the metal film as hot electrons. Some of the hat electrons have sufficient energy to pass over the cathode surface barrier into the vacuum. tunnel diode-Also called Esaki diode. 1. A pn diode to which has been added a large amount of impurity. The tunnel diode has high-speed charge movement and a negative-resistance region above a minimum level of applied voltage. With the addition of suitable external circuits, it can be used as an oscillator or amplifier. 2. A two-layer device similar to the rectifier diode. As a small voltage is applied, current starts to flow. Increase the voltage a little more and current drops to zero. Add still a little more voltage and the current increases again. At still higher voltages it responds like an ordinary diode. That first surge of current is called tunneling. 3. -A heavily doped junction diode based on tunneling effect: the piercing of a potential barrier by a low-energy electron. Has a forward negative resistance, and is an excellent low-noise microwave amplifier. It has no upperfrequency limitation. 4. A diode utilizing the tunnel effect. It gives rise to negative differential conductance in a

tunnel effect

- turnover pickup

808

POSITIVE ELECTRODE

POSITIVE ELECTRODE

ELECTRODE

ELECTRODE

Junctions.

Symbol. I

Ip

VP

=

PEAK CURRENT

VV

vs

"

Characteristic.

Tunnel diode. certain range of the forward direction of the currentvoltage characteristic. tunnel effect-1. The piercing of a potential hill by a carrier, which would be impossible according to classical mechanics, but the probability of which is not zero according to wave mechanics, if the width of the hill is small enough. The wave associated with the carrier is almost totally reflected on the first slope, but a small fraction crosses the hill. 2. In a pn transition region, a process whereby conduction occurs through a potential barrier and in which electrons pass in either direction between the conduction band in the n-region and the valence band in the p-region. The tunnel effect, unlike the diffusion of charge carriers, involves electrons only and is for all purposes an instantaneous process. tunneling-An observed effect of the ability of certain atomic particles to pass through a barrier that they cannot pass over because of the required energy level. It is based on a law of quantum mechanics that predicts that the particles have a finite probability for tunneling according to their quantum-mechanical nature. tunnel rectifier-A tunnel diode that has a relatively low peak-current rating in comparison with other tunnel diodes employed in memory-circuit applications. tunnel resistor-A resistor containing a thin layer of metal plated across a tunneling junction, so that the characteristics of a tunnel diode and an ordinary resistor are combined. tunnel triode-A transistorlike device in which the emitter-base junction is a tunnel diode and the collectorbase junction is a conventional diode. tunneluminescence -The emission of light from a phosphor film deposited on the surface of a thin-film metal-oxide-metal sandwich. turbidimeter- See opacimeter. turbulence amplifier- 1. Fluidic digital element using laminar-to-turbulent flow transition to create the control effect. 2. A fluidic device in which the power jet is at a pressure such that it is in the transition region of laminar stability and can be caused to become turbulent by a secondary jet or by sound. turn -One complete loop of wire. turnaround time- 1. The interval between the time at which a job is submitted to a batch processing system

and the time at which the results are returned. 2. The actual time required to reverse the direction of transmission in a half-duplex circuit. For most communications facilities, time is required for line machine reaction. (A typical time is 200 milliseconds on a half-duplex telephone connection.) 3. The period required for half-duplex modems to reverse the direction of transmission on dialup or two-wire leased lines. This includes the time for reversing the echo suppressors used on the two-wire simplex paths between telephone central offices. These suppressors are placed between central offices to prevent signals from one transmission path from crossing over into another. Also, for synchronous modems, turnaround time covers line equalization and bit synchronization. A full-duplex modem has no turnaround time when used in a point-to-point link, since it can transmit and receive information simultaneously. turn factor-Under stated conditions, the number of turns that a coil of given shape and dimensions placed on a core in a given position must have for a coefficient of self-inductance of 1 henry to be obtained for the core. turnkey- 1. A computer console containing a single control, usually a power switch, that can be turned on and off only with a key. 2. A design and/or installation in which the user receives a complete running system 3. Pertaining to a computer system sold in a ready-to-use state. turn-off delay time-The time interval between occurrence of the trailing edge of a fast input pulse and the occurrence of the 90-percent point of the negative-going output waveform. turn-off reversal -A polarity reversal of the output of the electronic power supply occurring from the turning off of the power of a regulated power supply. turn-off thyristor-A thyristor that can be turned from the on state to the off state, and vice versa, with appreciable gain by applying control signals of appropriate polarities to the gate terminal. turn-off time-The time that a switching circuit (gate) takes to stop the current in the circuit it is controlling. turn-on d e l a y time-The time interval from the occurrence of the leading edge of a fast input pulse to the occurrence of the 10-percent point of the positivegoing output waveform, assuming that the rise time of the incoming pulses is 0.1 of the rise time of the element to be measured under loaded conditions. turn-on overshoot-Overshoots occurring from the turning on of power of a regulated power supply. turn-on reversal -A polarity reversal of the output of the power supply occurring from the turning on of the power supply of a regulated power supply. turnover Cartridge -A phonograph cartridge adapted, by the use of two styli, to play both large- and fine-groove records. turnover frequency- 1. In disc recording, the frequency below which constant-amplitude recording is used and above which constant-velocity recording is employed. 2. The knee of the tone control or filter frequency response curve. Though normally thought of as the frequency at which the control begins to have its effect, the turnover point is actually the frequency at which response has already been altered by 3 dB relative to the unfiltered signal. Some tone controls and filters offer a choice of turnover frequencies that are usually switch-selected. turnover pickup- Also called dual pickup. A pickup designed for playing both standard and microgroove records, using a single magnetic structure. See also turnover cartridge.

turns ratio - twin lead

Turntable.

turns ratio-The ratio of the number of turns in the primary winding to the number in the secondary winding of a transformer. turnstile antenna-An antenna composed of two dipole antennas normal to each other and with their axes intersecting at their midploints. Usually the currents are equal and in-phase quadrature. turntable-1. The round platter on which a phonograph record rests during cutting or playback. Also refers to the platter and its driving motor and associated parts, as a high-fidelity component. 2. In tape recording, the rotating flat disc on which the reel (or, in some professional machines, the tape “pie”) lies slightly raised above the recorder’s front or top panel. The turntable is usually fitted with a center spindle and gripping keys of some kind to keep the reel centered and prevent it from slipping against the rotation of the turntable. turntable rumble-See rumble, 1. turret-A revolving plate mounted at the front of some television cameras and carrying two or more lenses of different types to permit rapid interchange of lenses. turret tuner -A television-receiver tuner containing a separate set of resonating circuit elements for each channel. Each set is mounted on an insulating strip or strips placed on a drum rotated from the channel position for the desired channel. TW- Abbreviation for television. TW camera-An optical device, consisting of lens, electron beam tube, and preamplifier, that converts an optical image into an electrical signal. 7V c h a n n e l -See television channel. TWI -Abbreviation for television interference. TV recording -A permanent record of video signals recorded1 photographically, electronically, or by other means, and which may be displayed through a television system or projected as a motion-picture film. TVRO -See television receive only. WIT -See TV terminal. terminal -Abbreviated TVT. A keyboard and electromagnetic deflection-type display unit that utilizes an ordinary (or modified) TV set as a display. tweaking -1. The process of adjusting an electronic receiver circuit to optimize its performance. 2. The fine tuning of a circuit with overly critical adjustments,

repeated several times until no further improvement in performance is obtained. This usually requires cansiderable skill and is not recommended as a requirement in circuits for production or construction by a hobbyist with limited technical resources. tweeter-Also called a high-frequency unit. 1. A speaker intended to reproduce the very high frequencies, usually those above 3000 Hz, in a high-fidelity audio system. Units may be ionic, ribbon, electrostatic, or dynamic types. 2. A high-frequency speaker (driver) specializing in treble reproduction. twelve p u n c h -A punch in the top row of a card. twenty-one type repeater -A two-wire telephone repeater in which one amplifier serves to amplify the telephone currents in both directions. The circuit is arranged so that the input and output terminals of the amplifier are in one pair of conjugate branches, while the lines in the two directions are in another pair. twenty-two type repeater-A two-wire telephone repeater with two amplifiers. One amplifies the telephone currents being transmitted in one direction, and the other the telephone currents being transmitted in the other direction. twilight -A scene illumination of approximately one footcandle. twin axial cable-A single shielded twisted-pair cable that has low-loss signal transmission and high noise immunity. twin cable- 1. A cable composed of two parallel insulated stranded conductors having a common covering. 2. A pair of insulated conductors twisted and/or sheathed or held together mechanically and not identifiable from each other in a common covering. twin check-A continuous check of computer operations accomplished by duplication of equipment and automatic comparison of results. twin coaxial cable-A configuration containing two separate, complete coaxial cables laid parallel or twisted around each other in one complex. twinflex-British word for twisted pair of wires or twin lead. twin lead -Also called twin line. A type of transmission line covered by a solid insulation and comprising two parallel conductors, the impedance of which is determined

twin line

- two-pilot regulation

by their diameter and spacing. The three most common impedance values are 75, 150, and 300 ohms.

Twin lead.

twin line-See twin lead. twinning -1. The intergrowth of two crystal regions having opposite oriented axes. Two types of twinning may occur: electrical and optical. In electrical twinning, the electrical senses of the crystal axes are reversed and the twinned regions will interfere with one another piezoelectrically. It is this effect that limits the hightemperature utility of quartz as a piezoelectric material. 2. A defect of natural quartz crystals, in which both the right and left quartz are in the same crystal. twin-T network-See parallel-T network. twin triode-Two triode vacuum tubes in a single envelope. twin wire-A cable composed of two small, parallel, insulated conductors having a common covering. twist -1. The progressive rotation of the cross section of a waveguide about the longitudinal axis. 2. The deviation from a plane surface measured from one corner to the comer diagonally opposite. 3. The difference (in decibels) between DTMF high-group and low-group signal levels, mathematically defined as 10 log (highgroup power)/(low-group power). Measured at the DTMF receiver, it's a function of both the level difference generated by the signal source and the gain-frequency characteristic of the transmission facility. twisted joint-A union of two conductors wound tightly around each other. A sleeve may be used, and it and the conductors twisted. twisted pair-1. A cable composed of two small insulated conductors twisted together without a common covering. The two conductors of a twisted pair are usually substantially insulated, so that the combination is a special case of a cord. 2. Two insulated wires (signal and return) that are twisted around each other in a spiral pattern mainly to cancel the effects of electrical noise. Since both wires have nearly equal exposure to any electrostatic or electromagnetic interference, the differential noise is slight. twister -A piezoelectric crystal that generates a voltage when twisted. twistor -A computer memory element containing inclined helical windings of magnet wire on a nonmagnetic wire, with another winding over the helix. Information is stored in the form of polarized helical magnetization. two-address -In a computer, having the property that each complete instruction includes an operation and specifies the location of two registers, usually one containing an operand and the other the result of the operation. two-address code -A computer code that uses two address instructions. two-address instruction -A computer instruction that includes an operation and specifies the location of two registers.

8 10

two-conductor jack-Receptacle

having two cir-

cuits, tip and sleeve.

two-cored screened cable -British term for twoconductor shielded cable. two-dimensional circuitry-See thin-film integrated circuit. two-fluid cell -A cell having unlike electrolytes at the positive and negative electrodes. two-hole directional coupler-A directional coupler that consists of two parallel coaxial lines in contact, with holes or slots through their contacting walls at two points one-quarter wavelength apart. With this device, a portion of the rf energy traveling in one direction through the main line may be extracted, while energy traveling in the opposite direction is rejected. It is necessary that one end of the secondary line be terminated in its characteristic impedance. two-level system-A laser that uses only two electron energy levels. Electrons in the ground state (level 1) are pumped to the excited state (level 2). The electrons then surrender their energy by stimulated emission and return to the ground state. two-out-of-five code-A type of positional notation in which each decimal digit is represented by five binary digits; two of the five are of one kind (for example, 1s) and three are of the other kind (for example, Os). two-part code- A randomized code with an encoding section and a decoding section. In the encoding section, the plaintext groups are arranged in alphabetical or other significant order, accompanied by their code groups in nonalphabetical or random order. In the decoding section, the code groups are arranged in alphabetical or numerical order and accompanied by their meanings given in the encoding section. two-phase- Also called quarter phase. Having a phase difference of 90 electrical degrees, or one quartercycle. t w o - p h a s e current-Two currents delivered through two pairs of wires at a phase difference of one quarter-cycle (90") between them. t w o - p h a s e dynamic-Pertaining to a dynamic logic circuit that uses two clock signals to control the processing of information through the circuit or logic system. two-phase, five-wire system -An alternatingcurrent supply in which four of its conductors are connected as in a four-wire, two-phase system and the fifth is connected to the neutral points of each phase and usually grounded. Despite its name, it is strictly a fourphase, five-wire system. two-phase, four-wire system -A system of alternating-current supply comprising two pairs of conductors, between one pair of which is maintained an alternating difference of potential displaced in phase by one-quarter of a period from an alternating difference of potential of the same frequency maintained between the other pair. two-phase, three-wire system -An alternatingcurrent supply consisting of three conductors. Between one conductor (known as the common return) and each of the other two, alternating differences of potential that are 90" out of phase with each other are maintained. two-piece contact-A contact made of two or more separate parts joined by swedging, brazing, or other means of fastening to form a single contact. This type provides the mechanical advantages of two metals but also has the inherent electrical disadvantage of difference in conductivity. two-pilot regulation-The use of two pilot frequencies within a transmitted band so that the change in

811 attenuation due to twist can be detected and compensated for by a regulator. two-plus-one address-Pertaining to an instruction that contains two operand addresses and one control address. tWO-FlOrt network- A network with two ports. two-pulse canceler -A moving-target indicator canceler that compares the phase variation of two successive pulses received from a target. It discriminates against signals with radial velocities that produce a Doppler frequency equal to a multiplle of the pulse-repetition frequency. two-quadrant multiplier-Of an analog computer, a multiplier in which operation is restricted to a single sign (of one input variable only. twos cOmp!ement-Pertaining to a form of binary arithmetic used in a computer to perform binary subtractions with addition techniques. The twos-complement negative of a binary number is formed by complementing each bit in the number andl adding 1 to the result. twos-complement biinary -An alternate and more ,widely used code to represent negative values. With this code, zero and positive values are represented as in nat,mal binary, and all negative values are represented in a twos-coniplement form. That is, the twos complement of ,a number represents a negative value so that interface to ,a computer or microprocessor is simplified. two-source f r e q u e n c y keying -Keying in which the modulating wave shifts the output frequency between predetermined values derived from independent sources. two-state device -A mechanical or electronic device that, except during the time it is changing between states, is intended to be olperated in either of two states or conditions. two-terminal network-A network that is connected by only two terminals to an external system. two-terminal-pair network- Also called a fourpole, quadripole, or quadrupole network. A network with four accessible terminals grounded in pairs. One terminal of each pair may coincide with a network node. two-tone keying -Keying in which the modulating wave causes the carrier to be modulated with one frequency for the marking condition and a different frequency for the spacing condition. two-tone modulating -A method of modulating in which two different carrier frequencies are used for the two signaling conditions. two t r a c k (half track)-A tape format in which the width of the tape is recorded in two parallel magnetic tracks, separated by an unrecorded guard band. As compared with four-track recording, the two-track system gives improved dynamic range and can be edited without loss of program, since the tape is passed in a single direction only. two-track r e c o r d e r -See dual-track recorder. two-track recording -On quarter-inch-wide tape, the arrangement by which only two channels of sound may be recorded, either as a stereo pair in one direction or as separate monophonic tracks (usually in opposite directions). two-value capacitor motor -A capacitor motor that uses different values of effective capacitance for starting and running. two-wattmeter m e t h o d -A method of measuring total power in a balanced or unbalanced three-phase system by adding the reedings of two wattmeters, each with its current coil in olne phase and its voltage coil connected between it and the third phase.

two-plus-one address -

ves

two-way amplifier-An amplifier in which the right and left channels of a stereo system are both amplified simultaneously by the same tubes, using pushpull circuitry but feeding one signal to the input grids in parallel instead of push-pull. The parallel and push-pull signals are then separated by two output transformers in a matrixing circuit. two-way communication -Communication between radio stations, each having both transmitting and receiving equipment. two-way radio -Radiotelephone communications between fixed points (base stations) and portable units. two-way repeater-See repeater. two-way s w i t c h -A switch used for conholling electrical or electronic equipment, components, or circuits from either of two positions. two-way system -A speaker in whch the low and the high frequencies are reproduced separately by two electrically independent speaker elements, each of which is provided with a suitable sound-radiating system. two-way, three-way, etc. -Refers to the number of frequency bands into which a speaker’s output is divided. A two-way system divides the spectrum into two such bands, one of which is handled by a woofer or woofers, the other by a tweeter or tweeters. A threeway system would have one or more woofers, midrange speakers, and tweeters. Systems up to five-way are available. two-wire channel-A two-way circuit for transmission in either direction. two-wire circuit-1. A metallic circuit formed by two conductors insulated from each other. It is possible to use the two conductors as either a one-way transmission path, a half-duplex path, or a duplex path. Also used in contrast with a four-wire circuit to indicate a circuit using one line or channel for transmission of electric waves in both directions. 2. A communications circuit that uses a single pair of wires for both transmitted and received information. two-wire repeater-A repeater that can be used for transmission in both directions over a two-wire circuit. In carrier operation, it usually makes use of the principle of frequency separation for the two directions of transmission. two-wire system -1. A system of electric supply comprising two conductors, with the load connected between them. 2. A system in which all communication takes place over a two-wire circuit or the equivalent. TWT- Abbreviation for traveling-wave tube. TWX- See teletypewriter exchange service, 2. Twystron -A very high power, hybrid microwave tube combining the input section of a high-power klystron with the output section of a traveling-wave tube. It is characterized by high operating efficiency and wide bandwidths. .TXT files-Text files. These are usually just plain text that can be read by most programs. type acceptance-Equipment authorization granted by the FCC to ensure that equipment will function properly in the service for which it has been accepted. type A facsimile-Facsimile comunicaiion in which the images are built up of lines of constant-intensity dots. type A waves -Continuous waves. type A1 waves -Unmodulated, keyed, continuous waves. type A2 waves -Modulated, keyed, continuous waves. type & waves-Continuous waves modulated by music, speech, or other sounds.

type A4 waves

- type-printed telegraphy

type waves -Superaudio frequency-modulated continuous waves, as used in a facsimile system. type & waves -Superaudio frequency-modulated continuous waves, as used in television. type As waves -Composite transmissions and cases not covered by type A through type As waves. typebar-A linear type element that contains all printable symbols.

812

type B facsimile -Facsimile communication in which the images are built up of lines of dots having a varying intensity (e.g., in telephotography and photoradio). type B waves -Keyed, damped waves. type-printed telegraphy-Telegraphy in which the message is automatically printed at the receiving station.

U

ultor element -The element that receives the highest dc voltage in a cathode-ray tube. ultra-audible f r e q u e n c y -See ultrasonic frequency. ultra-audion -Any of several special vacuum-tube circuits employing regeneration. ultra-audion circuit-A regenerative detector circuit in which a parallel-resonant circuit is connected between the grid and the plate of a vacuum tube, and a variable capacitor is connected between the plate and cathode to control the amount of regeneration. ultra-audion oscillator-A variation of the Colpitts oscillator in which the resonant circuit employs a transmission-line section.

UART-See universal asynchronous receivedtransmitter. ubitron-An amplifier or oscillator in which an undulating electron beam interacts with an rf wave. The kinetic energy of the beam is converted into rf energy (0type interaction). The undulation of the beam is produced by a periodic magnetic field. This field gives the beam a transverse velocity component that interacts with the rf wave. U-bolt-A U-shaped bolt threaded on both ends, for fastening antennas to masits. UG-The two-letter designation that precedes the number on connectors for coaxial cable. It means Universal Government. UHF - 1. Abbreviation for ultrahigh frequency. 2. In television, a term used to designate channels 14 through 69. UJT -Abbreviation fcrr unijunction transistor. UL -Abbreviation for Underwriters Laboratories, Inc. UL certificated-For certain types of products that have met UL requirements and for which it is impractical to apply the UL Listing Mark or Classification Marking to the individual product, ,a certificate is provided that the manufacturer may use to identify quantities of material for specific job sites or to identify field-installed systems. UL listed -Signifies that production samples of the product have been found to comply with established Underwriters Laboratories’ requirements and that the manufacturer is authorized to use the Laboratories’ Listing Marks on the listed products that comply with the requirements, contingent on the followup services as a check of compliance. ultimately controlled variable -The quantity whose control is the end purpose of an automatic control system. ultimate sensitivity or threshold -One-half the dead band in a graphic recorder. When the instrument is balanced at the center of the dead band, it denotes the minimum change in measured quantity required to initiate pen response. u!timate trip current-The smallest value of current that will cause tripping of a circuit breaker under a given set of ambient conditions. ultimate trip limits-The values of overload of a circuit breaker at which the minimum and maximum limits of the time-current curve become asymptotic; Le., the limits of current that will trip or not trip the breaker “ultimately.” Minimum and maximum limits of ultimate trip are often called calibration. ultor- An adjective used to identify the picture-tube anode or element farthest from the cathode, the anode to which the highest voltage is applied, or the voltage itself (e.g.$ the ultor anode is the second anode of the picture tube, and the ultor voltage is the voltage applied to it).

FIF AC OUTPUl

P

Ultra-audion oscillator.

Ultrafax-A trade name of RCA for a system in which printed information is transmitted by radio, facsimile, and television at high speeds. ultrahigh frequency- Abbreviated UHF. Frequency band: 300 to 3000MHz. Wavelength: 100 to IO centimeters. ultrahigh-frequency canverter-A circuit used to convert UHF television signals to VHF in order to permit UHF television reception on a VHF receiver. ultrahigh-frequency generator- Any device for generating ultrahigh-frequency alternating currents (e.g., a conventional negative-grid generator; a positive-grid, or Barkhausen, generator; a magnetron; and a velocitymodulation, or electron-beam, generator such as the klystron). ultrahigh-frequency loop-Generally a singleloop antenna used in ultrahigh-frequency work to secure a nondirectional radiation pattern in the plane of the loop. The doughnut-shaped pattern is perpendicular to the loop.

813

ultrahigh-frequencytranslator

- ultrasonicfrequency

ultrahigh-frequency translator-A televisionbroadcast translator station that transmits on a UHF TVbroadcast channel. ultralinear amplifier-A class AB or B audio amplifier using pentodes or high-power-output beampower tubes whose screen voltages are taken from taps on a specially wound output transformer rather than from a fixed dc source. This form of operation results in a considerable decrease in distortion in high-fidelity systems. ultramicrometer-An instrument for measuring very small displacements by electrical means (e& by the variation in capacitance produced by the movement being measured). ultramicrowave-Having wavelengths of about lo-’ to iow4cm. ultrashort waves-Radio waves shorter than 10 meters in wavelength (about 30 MHz in frequency). ultrasonic-1. Having a frequency above that of audible sound- i.e., between sonic and hypersonic. 2. Sound waves that vibrate at frequencies beyond the hearing power of human beings (above 16,000 Hz). Commercial and military applications include ultrasonic cleaning, gauging, cutting, detection instruments, and welding. ultrasonic bond-A contact area where two materials are joined by means of ultrasonic energy and pressure. ultrasonic bonding- 1. A process for joining metal parts by the scrubbing action and energy transfer of a tool vibrating at an ultrasonic rate. This method is used to attach leads to pads on silicon devices. 2. A process involving the use of ultrasonic energy and pressure to join two materials. 3. A joining technique for wire and lead attachment that employs pressure plus an ultrasonically introduced scrubbing action to form a molecular bond.

ALUMINUM ORGOLD WIRE

ULTRASONIC VIBRATION

CAPILLARY TIP

\ A BO

Ultrasonic bonding.

ultrasonic brazing -See ultrasonic soldering. ultrasonic cleaner-A device using ultrasonic pressure waves to clean objects. ultrasonic cleaning-A method of cleaning that uses cavitation in fluids caused by applying ultrasonic vibrations to the fluid. ultrasonic cleaningequipment-Ultrasound used in the cleaning of metal and optical parts by virtue of its vibration rates. Large acoustic forces break off particles and contaminants from surfaces. ultrasonic cleaning tank-A heavy-gage, polished stainless-steel tank with transducers mounted on the bottom or sides. ultrasonic coagulation-The bonding together of small particles by the action of ultrasonic waves. ultrasonic cross grating-Also called grating. The two- or three-dimensional space grating produced

8 14

Ultrasonic cleaning tank.

when ultrasonic beams having different directions of propagation intersect. ultrasonic delay line- Also called an ultrasonic storage cell. A contained medium (usually a liquid such as mercury) in which the signal is delayed because of the longer propagation time of the sound waves in the medium. ultrasonic densitometer- An instrument device for determining the thickness or density of an object or material based on the time required for an ultrasonic signal to penetrate to a receiver and/or echo back to a receiver adjacent to another transmitter. ultrasonic detector-A device-either mechanical, electrical, thermal, or optical-for detecting and measuring ultrasonic waves. ultrasonic diagnosis-A method of obtaining information from within the body in a visual presentation without employing ionizing radiation. It differs from Xray in that the form of energy used is high-frequency sound, or ultrasound, which is inaudible. The sound is transmitted in very brief pulses followed by relatively lengthy “silent” intervals. Also, in contrast to X-ray techniques, in which the film is placed behind the tissue being examined, ultrasonic information is picked up at the original point of transmission in the form of echoes from internal structures. These returning echoes are converted to electrical energy and displayed in either a static or dynamic pattern, as desired, on a cathode-ray-tube screen. ultrasonic disintegrator- An apparatus for using the pressure wave produced by an ultrasonic generator to tear cells apart. ultrasonic drill-A special type of drill that has a magnetostrictive transducer attached to a tapered cone that serves as a velocity transformer. With an appropriate tool, practically any shape of hole can be drilled in brittle and hard material. ultrasonic flaw detector -Equipment comprising an ultrasonic generator, transducer, detector, and display; used to detect flaws or cracks in solids from the reflection pattern of ultrasonic signals observed on a cathode-ray tube. ultrasonicfrequency -Also called an ultra-audible frequency. 1. Any frequency above the audio range, but commonly applied to elastic waves propagated in gases, liquids, or solids. 2. Sound frequencies that are above the range of human hearing; approximately 20,000 Hz and higher.

ultrasonic generator

815

ultrasonic generator- A device for producing mechanical vibrations at frequencies above the range of human hearing. Typically, such a device consists of an rf oscilllator whose output is applied to a piezoelectric crystal. ultraisonic grating constant-The distance between diffracting centers of the sound wave producing particul,~light-diffraction spectra. ultralsonic immersion -Cleaning technique depending on cavitation (rapid formation of tiny bubbles in a cleaning liquid). Cavitation is created by ultrasonic, high-intensity sound waves. The agitation of imploding bubbles scrubs the immersed part. ultrasonic inspection -A nondestructive testing method of locating internal defects in a part by sending ultrasonic impulses (inaudible high-frequency sound waves of 0.5 to 11 megahertz) into the part and measuring the time required for these impulses to penetrate the material, be reflected from the opposite side or from the defect, ;and return to the sending point. ultrasonic level detector-A level detector consisting of an ultrasonic receiver and transmitter located in one wall of a container or vessel. With nothing to obstruct the beam, it is reflected from the opposite wall. When the level of the liquid or other material in the container reaches the beam, the liquid or material acts as a reflector, thus reducing the reflection time and indicating that a given level has been reached. ultraisonic light diffraction-The formation of optical (diffractionspectra when a beam of light is passed tbrough a longitudinal sound-wave field. The diffraction results from the periodic variation of the light refraction in the sound field. ultraisonic light modulator-A device containing a fluid that, by action of ultrasonic waves passing through the fluid, modulates a beam of light passed transversely through the fluid. ~ ~ ~ r a ~ material ~ o n i cdispersion -The production of suspensions or emulsions of one material in another by the actiton of high-intensity ultrasonic waves. u%trzisonic motion detector-A sensor that detects the motion of an intruder through the use of ultrasonic generating and receiving equipment. The device operates by filling a space with a pattern of ultrasonic waves; the modulation of these waves by a moving object is detected and initiates an alarm system. ultrasonic plating -The chemical or electrochemical deposition and bonding of one or more solid materials to the surface of another material by the use of vibrational wave energy. robe-A rod for directing ultrasonic force, used in a disintegration or foreign-body location application. ultraasonic rejection-The level of rejection of the 19-kHz oilot tone and 38-kHz voltage-controlled oscillator frequency in a stereo FM receiver.?he intrinsic rejection of a stereo decoder is the logarithmic ratio of the level of 19-kHz and 38-kHz reference tones with only the standard deemphasis filter at the decoder outputs. Itrasonics-The general subject of sound in the frequency range above 15 kilohertz. ultrasonic sealing -A film sealing method based on the application of vibratory mechanical pressure at ultrasonic frequencies (20 to 40 IcHz). Electrical energy is converted into ultrasonic vibrations by a magnetostrictive or piezoelectric transducer. The vibratory pressures at the film interface in the sealing area produce localized heat losses that cause the plastic surfaces to melt, thereby forming the seal. ~ ~ ~ r soldering~ ~ ~ o1. ~ A method i c of forming a nonporous, continuously metallic connection between

- ultraviolet

metal or alloy parts without necessarily employing chemicals or mechanical abrasives. Instead, vibrational wave energy, heat, and a separate alloy or metal having a melting point below 800°F (427°C) and also below that of the metals or alloys being joined are used. 2. Soldering in which the surface oxide coating of the base metal is removed by ultrasonic vibration. ultrasonic space grating-Also called grating. A periodic spatial variation in the index of refraction caused by the presence of acoustic waves within the medium. ultrasonic storage cell -See ultrasonic delay line. ultrasonic stroboscope-A light intempter in which the light beam is modulated by an ultrasonic field. ultrasonic therapy-The use of ultrasonic vibrations for therapeutic purposes. ultrasonic thickness gage- A thickness gage in which the propagation time of an ultrasonic beam through a sheet of material is translated into a measure of the thickness of the material. ultrasonic transducer-A device that takes the electrical oscillations produced by the ultrasonic generators and transforms them into mechanical oscillations. Typical transducer materials are piezoelectric (e.g., quartz or barium titanate) or magnetostrictive (e.g., nickel).

LIVE LEAD f--

GROUND LEAD

BAAaUM

T TAhAlE OUARTZ

Ultrasonic transducer.

ultrasonic waves -Waves having a frequency in the ultrasonic range. ultrasonic welding -1. A process that joins two pieces of metal by a form of diffusion bonding. The metals to be welded are clamped between a rigid anvil and a probe, which is vibrated at ultrasonic frequency. The vibration removes any surface oxide film by a simple mechanical scrubbing action, thus exposing the metal surfaces. Then plastic deformation caused by the imposed mechanical clamping load causes the atom movement necessary to joint the two crystal lattices, creating a strong, bonded, monolithic structure at the joint line. Some heat is generated by friction caused by the rubbing of the one surface upon the other. This heat undoubtedly aids the diffusion mechanism that occurs but is obviously insufficient to cause welding by itself. 2. Method of fusing two plastic parts by ultrasonic vibrations that are produced by mechanical motion of a converter, expanding and contracting some 20,000 times per second. The vibratory energy is channeled through a horn and applied to thermoplastic materials. This creates the frictional heat to produce a molecular interaction and weld materials. ultrasonic wire bonder-Equipment unit that fastens fine wire onto a substrate by use of ultrasonic energy. ultrasonography- A medical diagnostic technique in which pulses of ultrasonic energy are directed into the body, and returning echoes are detected. ultraviolet-I. Pertaining to electromagnetic radiations at wavelengths beyond the violet end of the spectrum of visible radiation. Because of the shorter wavelengths (200 to 4000 angstrom units), the photons of ultraviolet light have enough energy to initiate most chemical reactions and to degrade some plastics. 2. The invisible region

ultraviolet erasable PROM

- underload relay

of the spectrum immediately beyond the violet end and between the wavelengths of approximately 1000 to 3800 angstroms. ultraviolet erasable PROM -See UV erasable PROM. ultraviolet lamp -1. A lamp providing a high proportion of ultraviolet radiation (e.g., arc lamps, mercuryvapor lamps, or incandescent lamps in bulbs of a special glass that is transparent to ultraviolet rays). 2. A type of lamp that emits a great quantity of ultraviolet radiation. This may be an arc lamp encased in a bulb of a glass that is transparent to ultraviolet rays. ultraviolet r a y s -Radiation in the ultraviolet region. umbilical cable-A lifeline cable used for the main power supply to a missile in order to launch it. It is attached by means of a connector, which detaches as the missile becomes airborne. (Usually seen as a cable waving like a snake alongside the missile as it moves off the launching pad.) umbilical connector -A device for connecting cables to a rocket or missile prior to launch. It is removed (unmated) from the missile at the time of launching. umbrella antenna-An antenna in which the wires are guyed downward in all directions from a central pole or tower to the ground, somewhat like the ribs of an open umbrella. unamplified b a c k bias- A degenerative voltage developed across a fast time-constant circuit within an amplifier stage itself. unbalanced- 1. Lacking the conditions for balance. 2. Frequently, a circuit having one side grounded. 3. Differential mutual impedance or mutual admittance between two circuits that ideally would have no coupling. unbalanced circuit-A circuit whose two sides are electrically unlike. unbalanced line-A transmission line in which the voltages on the two conductors are not equal with respect to ground (e.g., a coaxial line). unbalanced output- An output in which one of the two output terminals is substantially at ground potential. unbalanced wire circuit-A circuit whose two sides are electrically unlike. unbianking-The turning on of the CRT beam. unblanking generator-A circuit for producing pulses that turn on the beam of a cathode-ray tube. unblanking pulse-A pulse that turns on the beam of a cathode-ray tube. unblocked record-A record contained in a file in which each block contains only one record or record segment. u n b o n d e d strain gage -A pressure-sensing element made up of resistance strain-gage wire elements arranged in a Wheatstone bridge. It can have two or four active arms, which respond to a pressure applied to the transducer. The unbonded strain-gage wires are suspended in air and are activated by a mechanism attached to a diaphragm or other pressure-responding element. unbundling-Kcing certain types of software and services separately from the hardware. uncertainty-A number or numbers assigned to a measurement as an assessment of all the errors associated with the process producing the measurement. See also accuracy. uncharged -Having a normal number of electrons and, hence, no electrical charge. unconditional-In a computer, not subject to conditions external to the specific instruction. unconditional jump-A computer instruction that interrupts the normal process of obtaining the instructions

816 in an ordered sequence and specifies the address from which the next instruction must be taken. unconditional transfer of control -In a digital computer that obtains its instructions serially from an ordered sequence of addresses, an instruction that causes the following instruction to be taken from an address that becomes the first of a new sequence. uncontrolled terminal-A user terminal that is online all the time and does not contain line-control logic for polling and calling. undamped natural frequency-The frequency at which a system with a single degree of freedom will oscillate, in the absence of damping, upon momentary displacement from the rest position by a transient force. undamped oscillations-Oscillations that have a constant amplitude for their duration. undamped wave- A wave whose amplitude does not change. undefined record-A record contained in a file in which the records have not been defined as being fixedlength records or variable-length records. underbunching-The condition whereby the buncher voltage of a velocity-modulation tube is lower than the value required for optimum bunching of the electrons. undercompounded-A generator in which the output voltage drops as the load is increased. undercurrent relay-A relay that functions when its coil current falls below a predetermined value. undercut-In a printed circuit board, the reduction of the cross section of a metal-foil conductor due to the removal of metal from beneath the edge of the resist by the etchant. undercutting-A cutting with too shallow a groove or with insufficient lateral movement of the stylus during sound disc recordings. underdamped-A degree of damping that is not sufficient to prevent oscillation in the output of a system following application of an abrupt stimulus. underdamping -1. In a system, the condition whereby the amount of damping is so small that the system executes one or more oscillations when subjected to a single disturbance (either constant or instantaneous). 2. Oscillation of the transducer output about a final steady value in response to a step change in the measurand. After an initial overshoot, the oscillation amplitude decreases. 3. See periodic damping. underflow- 1. In a computer, the generation of a quantity smaller than the accepted minimum (e.g., floating-point underflow). 2. Pertaining to the condition that arises when a machine computation yields a nonzero result that is smaller than the smallest nonzero quantity that the intended unit of storage is capable of storing. (Contrast with overflow.) 3. When a calculator’s capacity is exceeded, some of the least significant digits are discarded and the resulting display is sometimes zero. underglaze-A glass or ceramic glaze applied to a substrate prior to the screening and firing of a resistor. underground cable-A cable installed below the surface of the earth. under insulation -The insulation under wire that is brought from the center of a coil over the top or bottom wall. underlap-Recorded elemental areas that are smaller than normal -specifically,the space between the recorded elemental area in one recording line of a facsimile system and the adjacent elemental area in the next recording line, or the elemental areas in the direction of the recording line. underload relay-A relay that operates when the load in a circuit drops below a certain value.

817 undermodulation- Insufficient modulation of a transmitter due to misadjustment or to insufficient modulation signal. underpass-A semiconductor component that permits two conductors to cross each other without a short circuit between them. Generally, it is in the form of a low-value resistor covered by a silicon dioxide layer that isolates the top conductor; the resistor is part of the bottom conductor. underpower relay-A relay that functions when the power decreases below a predetermined value. underscan-Reducing the height and width of the video picture so that the edges, and, thus, portions of blanking, can be observed. undershoot- 1. The initial transient response to a unidirectional change in input, which precedes the main transition and is opposite in sense. See also precursor. 2. The crossing of the base line in the direction opposite to that of the principal pulse, but with insufficient amplitude to be considered a bipolar pulse. underthrow distortion -Distortion resulting when the maximum amplitude of the signal wavefront is less than the steady-state amplitude that would be attained by a prolonged signal wave. undervoltage protection-Also called low-voltage protection. The effect of a device to cause and maintain the interruption of power to the main circuit upon the reduction or failure of voltage. undervoltage relay-A relay that operates when its coil voltage falls below a predetermined value. underwater sound projector-An electroacoustic transducer designed to convert electric waves into sound waves, which are radiated in water for reception at a distance. ndienwiters Laboratories, Inc. -Abbreviated UE. 1. An independent, nonprofit product-safety testing and certification organization that operates laboratories for the examination and testing of devices, systems, and materids to ensure that they meet standards for safety. Acceptance is usually indicated by tags or by labels on devices showing the words “UL Approved” or “UL Listed.” 2. A corporation supported by some underwriters for the purpose of establishing safety standards on types of equipment and components. undistorted wave-A periodic wave in which both the attenuation and the velocity of propagation are the same for all sinusoidal components, and in which the same sinusoidal component is present at all points. undisturbed-one output-A 1 output of a magnetic cell to which no partial-read pulses have been applied since that cell was last selected for writing. undisturbed-zero output-A 0 output of a magnetic cell to which no partial-write pulses have been applied since that cell was last selected for reading. unflred tube-The condition of tr, atr, and pre-tr tubes when there is no radio-frequency glow discharge at either the resonant gap or the resonant window. unfrrrlableantenna -A device that can be unfolded to fonri a larger antenna. ungrounded-Not intentionally connected to ground except through high-impedance devices. ungrounded system -A system in which no point is directly connected to earth except through potential or ground-detecting transformers or other very high impedance devices. ~ n i a x ~ amagnetic l anisotropy-A property of magnetic thin film in which the direction of magnetization is always parallel to the easy axis unless an external force acts up09 it.

undermodulation

- unijunction transistor

uniconductor waveguide -A waveguide consisting of a rectangular or cylindrical metallic surface surrounding a uniform dielectric medium. unidirectional -Flowing in only one direction (e.g., direct current). Unidirectionalantenna -An antenna with a single, well-defined direction of maximum gain. unidirectional bus-A bus used by any individual device for one-way transmission of messages only, that is, either input only or output only. unidirectional Coupler-A directional coupler that samples only one direction of transmission. unidirectional current-A direct current; ie., one that is always positive or always negtitive-never alternating. unidirectional log-periodic antenna -A broadband antenna in which the cut-out portions of a logperiodic antenna are placed at an angle to each other to produce a unidirectional radiation pattern whose major lobe is in the backward direction, o f f the apex of the antenna. The impedance and the radiation pattern are essentially constant for all frequencies. unidirectional microphone-A microphone that is most sensitive to sounds arriving at it from one direction. unidirectional pulses -Single-polarity pulses that all rise in the same direction. unidirectional pulse train-A pulse train in which all pulses rise in the same direction. Unidirectional transducer-A transducer that responds to stimuli in only one direction from 2 reference zero or rest position. uniform corrosion-A form of corrosion that results from shifting anodic and cathodic areas evening out metallic thinning. In more complex cases, erosion constantly deprives the metal of its protective coating (e.g., oxides), exposing it to continuing corrosion. uniformfield -A field in which the scalar (or vector) has the same value at every point in the region under consideration at that instant. uniformity--In terms of magnetic tape properties, a figure of merit relating to the ability of the tape to deliver a steady and consistent output level upon being recorded with a constant input. Usually expressed in decibel variation from average at a midrange frequency. uniform line -A line with substantially identical electrical properties throughout its length. uniform plane wave-A plane wave with constantamplitude electric and magnetic field vectors over the equiphase surfaces. Such a wave can only be found in free space, at an infinite distance from the source. uniform precession-The condition in which the magnetic moments of all atoms in a sample are parallel and precess in phase about the magnetic field. Uniform precession occurs in the regions where the magnetic field is uniform. A spin wave is a phase distortion of this condition. uniform waveguide-A waveguide whose physical and electrical characteristics do not change with distance along its axis. uniground- Also called single-point ground. A single point in an electrical system connected to ground to eliminate noise currents. unijunctisn transistor- Abbreviated UJT. 1. Formerly called a double-base diode. A three-terminal semiconductor device that exhibits a stable negative-resistance characteristic between two of its terminals. It is this negative-resistance feature that makes the UJT suitable for the applications with which it is associated-thyristor trigger circuits, oscillator circuits, timing circuits, bistable

unilateral area track

- unipole I

818

EMITTER

A

RAW POWER

JUNCTION

IBASE1

II

H

1

I -

I

-

I

UNDIRECTIONAL} SWITCH

SYNCHRONIZER

UNlOlRECTlONAL

i

T

Static power supply.

Schematic.

Unijunction trcansistor.

circuits, etc. 2. A type of transistor that has easily controllable on-off characteristics and excellent voltage-sensing characteristics. 3. A three-terminal semiconductor having only one pn junction and exhibiting a stable open-circuit negative-resistance property. unilateralarea track-A sound trackin which only one edge of the opaque area is modulated in accordance with the recorded signal. However, there may be a second edge modulated by a noise-reduction device. unilateral bearing-A bearing obtained with a radio direction finder having unilateral response, eliminating the chance of a 180" error. unilateral conductivity-Conductivity in only one direction (e.g., in a perfect rectifier). unilateral element -A two-terminal element with a zero voltage-to-current characteristic (or the equivalent) on one side of the origin. unilateralization -A special case of neutralization in which the feedback parameters are completely balanced out. In transistors, these feedback parameters include a resistive in addition to a capacitive component. Unilateralization changes a network from bilateral to unilateral. unilateral network-1. A network in which any driving force applied at one pair of terminals produces a response at a second pair, but yields no response when the driving force is applied in the other direction. 2. A network that does not pass currents and signals equally well in both directions. For example, a network containing a rectifying element. unilateral switch -A semiconductor device similar to a miniature SCR. It switches at a fixed voltage that depends on its internal construction. unilateral transducer-See unidirectional transducer. uninterruptible power system-A solid-state power conversion system to provide regulated ac power to critical loads. Such a system provides uninte.rrupted power even during brownouts and blackouts. unipolar- 1. Having but one pole, polarity, or direction. With respect to amplifier power supplies, having an output that varies in only one polarity from zero and, therefore, always contains a dc component. 2. See neutral transmission. 3. Refers to transistors in which the working current flows through only one type of semiconductor

t 0

GENERATOR

Buffered power supply.

UniiatemptWe power system material, either n-type or p-type. In unipolar transistors, the working current consists of either positive or negative electrical charges, but never both. All MOS IC transistors are unipolar. Unipolar (MOS) IC transistors operate slower than bipolar IC transistors, but take up much less space on a chip and are much more economical to manufacture. unipolar field-effect transistor -A field-controlled majority-carrier device wherein the conductance of a semiconductor channel is modulated by a transverse electric field. The field is controlled by the combination of gate bias V,, and the net voltage Vd, between channel drain and source. unipolar pulse-A pulse that has appreciable amplitude in only one direction. unipolar transistor- 1. A transistor in which charge carriers are of only one polarity. See also fieldeffect transistor. 2. Transistor formed from a single type of semiconductor material, either n-channel or p-channel, as employed in field-effect transistors. CONTROL

UnQolar transistor. unipole- 1. An all-pass filter section with one pole and one zero. 2. A hypothetical antenna that radiates

819 and receives equally in all directions. See aZso isotropic antenna. cathaide -See indirectly heated cathode. unipotential electrostatic lens- A simple electrostatic lens having a focus that is controlled by a single potential difference. unit-I. A computer portion or subassembly that constitutes the means of accomplishing some inclusive operation or function (e.g., an arithmetic unit). 2. The specific magnitude of a quantity set apart by appropriate definitiom and serving as a basis for the comparison or measurement of like quantities; the lowest standard quantity in any system (of measurement. The unit of electrical energy, for example, is the kilowatthour. 3. One of the transceivers covered by a CB station license when more than one transceiver is used. 4. An assembly or device capable of independent operation. unit-area acoustic impedance -See specific acoustic impedance. unitary code-A code having only one digit, the number of times it is repeated determining the quantity it represents. unit charge-The electrical charge that will repel a force of 1 dyne on an equal and like charge 1 centimeter away in a vacuum, assuming each charge is concentrated at a point. United States of America Standards Institute-See American National Standards Institute. unit iintewal-See signal element. unit length-The basic element of time for determining code speeds in message transmission. unit load-The elecirical load imposed on a driver output by the receiver inputs. The actual values for a unit load are specified by the device manufacturer. The unit load is helpful to a logic system designer in determining bus drive requirements. unit magnetic pole-A pole with a strength such that when it is placed 1 centimeter away from a like pole, the force between the two is 1 dyne. unitor-In computers, a device or circuit that performs a function corresponding to the Boolean operation of union. See also OR gate. unit pulse-See baud. unit recordequipment -Equipment using punched cards as input data, such as collators, tabulating machines, etc. unit sequence starting relay-A device that functions to start the n e a available unit in a multipleunit equipment on the failure or on the nonavailability of the normally preceding unit. unit sequence switch-A switch used to change the sequence in which units may be placed in and out of service in multiple-unit equipment. unit step current (off voltage)-A current (or voltage) that undergoes an instantaneous change in magnitude from one constant level to another. unit substation transformer-A transformer that is mechanically and electrically connected to and coordinated in design with one or more switch-gear or motorcontroUed assemblies or combinations thereof. unit torque gradient-The torque gradient of a synchro, measured when the synchro is electrically connected to another synchro of the same size. unit under test -'4bbreviated UUT. Any system, set, subsystem, assembly, or subassembly undergoing testing. unitunnel diode-1. A diode similar to a tunnel diode, but specially treated to give peak reverse currents in the microampere region while providing high forward

unipotential cathode

- universe

conductance at low voltage levels. 2. A tunnel diode whose peak and valley point currents are approximately equal. unity coupling-Perfect magnetic coupling between two coils, so that all the magnetic flux produced by the primary winding passes through the entire secondary winding. unity gain-An amplifier or active circuit in which the output level is the same as the input level has unity gain. unity-gain bandwidth -The frequency at which the open-loop gain reaches unity, based on a 6-dB-peroctave crossing. It is a measure of the gain-frequency product of an amplifier. unity-gain crossover frequency- The frequency at which the curve of open-loop voltage gain of an amplifier crosses through unity gain, or zero decibels. unity power factor-A power factor of 1.0. It is obtained only when current and voltage are in phase (e.g., in a circuit containing only resistance, or in a reactive circuit at resonance). universal asynchronous reeeiverhransmitter-Abbreviated UART. 1. A device that will interface a word-parallel controller or data terminal to a bit-serial communication network. 2. A serial-to-parallel and parallel-to-serial converter. 3. An integrated circuit designed to handle serial/paraUel/serial conversion and transmission of data. 4. Commonly used LSI circuit that serves as a universal, single-package, TTL-compatible, full-duplex, serial communication line controller and data interface. 5. A sophisticated integrated circuit that accepts serial data and retransmits it as parallel data and vice versa. 6. A two-way, serial-to-parallel (and reverse) converter chip. UARTs are either dedicated or programmable; the latter permits selection of variables such as type of parity and word length. UART clock frequency is generally 16 times the baud rate. 7.A logic circuit that converts parallel information to an asynchronous serial format, and serial information to a paraliel format. Useful for connecting processors having parallel data buses to serial Ji'O lines. 8. A logic circuit that can connect a parallel I/O bus to either an asynchronous or a synchronous serial VO line. universal motor- 1. A series-wound motor designed to operate at approximately the same speed and output on direct current or on a single-phase alternating current of not more than 60 hertz and approximately the same rms voltage. 2. A motor with wound field and annature, with a commutator to make dc operation possible. When all windings are connected in series, it will operate on ac as well as dc, although the higher the ac frequency the more carefully the iron must be laminated to prevent excess eddy-current heating loss. universal output transformer- An output transformer having a number of taps on its winding. By proper choice of connections, it can be used between the audiofrequency output stage and the speaker of practically any radio receiver or audio amplifier. universal pattern-Circuit board pattern accommodating standard package configurations, such as DIPS. universal product code-See UPC. universal receiver -Also called an ac/dc receiver. A receiver with no power transformer and, thus, capable of operating from either ac or dc power lines without changes in its internal connections. universal shunt-See Ayrton shunt. universaltime- AbbreviatedUT. Also called Greenwich mean time and Greenwich civil time. A standard based on the rotation of the earth on its axis, with reference to the position of the sun. universe -See population.

UNlX

- urgency

UNIX- A complex and powerful multiuser computer operating system written in the C language originally developed, marketed, and trademarked by AT&T. It needs a computer with a large amount of RAM (random-access memory or storage capacity). UNIX allows a computer to handle multiple users and programs simultaneously and has TCP/IP built-in. It is the most common operating system for servers on the Internet. It also allows software. to be moved (known as porting) to computers of different sizes or types. UNIX is available in several related versions. unload-In a computer: 1. To remove the tape from the columns of a recorder by raising or lowering the recording head. 2. To remove a portion of the address part of an instruction. 3. See also dump. unloaded antenna-An antenna with no added inductance or capacitance. unloaded applicator impedance (dielectric heaters) -The complex impedance measured at the point of application and at a specified frequency without the load material in position. unloaded line-A line with no loading coils. unloaded Q (switching tubes) -Also called the intrinsic Q. The Q of a tube unloaded by either the generator or termination. unloading amplifier-An ampliiier capable of reproducing or amplifying a given voltage signal while drawing negligible current from the voltage source. unloading circuit-In an analog computer, a computing element or combination of computing elements capable of reproducing or amplifying a given voltage signal while drawing negligible current from the voltage source, thus decreasing the loading errors. unmodulated-Having no modulation; e.g., a carrier that is transmitted during moments of silence in radio programs, or a silent groove in a disc recording. unmodulated groove -Also called a blank groove. In mechanical recording, the groove made in the medium with no signal applied to the emitter. unoriented-A structure in which the crystallographic axes of the grains of a metal are not aligned to give directional magnetic properties. unpack-In a computer, to separate combined items of information, each into a separate machine word. unsaturated logic-A form of logic containing transistors operated outside the region of saturation; for example, current-mode logic (CML) and emitter-coupled logic (ECL). unserved energy-The amount of energy not delivered as a result of an equipment outage. untuned-Not resonant at any of the frequencies being handled. unusable samples- In random-sampling-oscilloscope technique, those samples not falling within the time window. unweighted noise-The measured noise level in electronic equipment, with a measuring device that is sensitive to a wide range of frequencies that extend beyond the audible spectrum. unwind-In a computer, to code all the operations of a cycle, at length and in full, for the express purpose of eliminating all red-tape operations. UPC-Abbreviation for universal product code. A product identification system designed to assign a unique number to every product in distribution. A 10-digit bar code, with the first 5 digits identifying the manufacturer, the second 5 identifying the item. Each digit is represented by the ratio of the widths of adjacent stripes and white areas. Used with optical checkout scanning devices that retrieve item price from a computer.

820 upconverter- 1. A device that increases the frequency of a transmitted signal. 2. A type of parametric amplifier that is characterizedby the frequency of the output signal being greater than the frequency of the input signal. update-1. To search a file (such as a particular record in a computer tape) and select one entry, then perform some operation to bring the entry up-to-date. 2. In a computer, to modify an instruction so that the address numbers in it are increased by a specified amount each time the instruction is executed. 3. Generally applied to computer files in which records are added, deleted, or amended to ensure that the latest information is contained in the file. update-response time -The interval between the entry of new data into a system and the display of that data. updating -The act of bringing information up to the current value. up/down counter- Also called reversible counter. A counter with the capability of counting in an ascending or descending order, depending on the logic present at the upldown inputs. uplink-1. Anrflinkfromasiteonthe earthorfrom an aircraft to a satellite. 2. The earth-to-geosynchronous satellite microwave link and related components, such as earth station transmitting equipment.The satellite contains an uplink receiver; uplink components in the earth station are involved with the processing and transmission of signals to the satellite. 3. The communicationspath from the earth to the satellite. 4. The earth station electronics and antenna that transmit information to a communication satellite for relay back to the ground. upload -1. The process of transferring communications instructions or data from terminals, including PCs, into a mainframe or host computer system. 2. To send a file from one computer to another via modem or other telecommunicationmethod. See also download. upper operating temperature -The maximum temperature to which a material can be subjected and still maintain specified operating characteristics within limits. upper sideband- 1. The higher frequency or group of frequencies produced by an amplitude-modulation process. 2. In carrier transmission,the band of frequencies that is higher than the carrier frequency. It is the sum of the instantaneous values of the carrier frequency and the modulating frequency. upset-duplex s y s t e m -A direct-current telegraph system in which a station between any two pieces of duplex equipment may transmit signals by opening and closing the l i e circuit and thereby upsetting the duplex balance. upset welding -A resistance-welding process wherein the weld is made simultaneously over the entire area of abutting surfaces or progressively along the joint with the aid of rolls or clamps that force the abutting surfaces together. The pressure is applied before heating starts and is maintained throughout the heating period. up time-1. The time during which an equipment is either operating or available for operation, as opposed to down time, when no productive work can be accomplished. 2. That element of active time during which an item is either alert, reacting, or performing a mission. up-time ratio-The quotient of up time divided by up time plus down time. urea plastic material -A thermosetting plastic material, with good dielectric qualities, used for radioreceiver cabinets, instrument housing, etc. urgency-The degree to which a process requires attention; determined by the process’s priority.

821

URL- Abbreviation for Uniform Resource Locator. An HTTP address used by the World Wide Web to specify a certain site. usable samples-In random-sampling-oscilloscope technique, those samples falling within the time window. USAlRT -Acronym for universal synchronous/asynchronous receiver/transmitter. See universal asynchronous receiverltransmitter. USASCII-Abbreviation for USA Standard Code for Information Interchange. The standard code, using a coded character set consisting of 7-bit coded characters (bits including parity check), for information interchange among data-processing communication systems and associated equipment. The USASCII set consists of control characters and graphic characters. Synonymous with ASCII. USASCSOCR-The United States of America Standard Character Set for Optical Characters. USASI -Abbreviation for United States of America Standards Institute, the successor to ASA (American Standards Association). USB-compatible -Universal Serial Bus Compatible. A new technology tlhat allows connection of many different kinds of peripherals to a PC using “hubs” to allow as many as 127 devices to be connected to a single attachment point. It can handle traffic up to 12 Mb/sec. scan-A paralkl reading method to prevent iguity in the readout of polystrophic codes at the code-position transitions by reading one to two sets of brushes, depending on the state of a control or selector bit. useful life-The total time a device operates between

selnet--A worldwide system of discussion groups, with comments passed among hundreds of thousands of machines. Usenet is completely decentralized, with over 10,000 discussion areas, called newsgroups. user-defined key-A key whose function or program can be changed, so that a command or sequence of c~mmandscan be executed with a single keystroke. Same as programmable key and soft-function key. Unlike a special-function key, a user-defined key may have a predefined purpose. user-friendly-Term used to describe computer hardware or software that is easy to use, by virtue

LBRL

- UVROM

of its design and the facilities that are offered to the user. user interface -The collection of screen formats, editing tools, commands, and software tools by which a user interacts with a computer. user-to-user service-A switching method that permits a direct user-to-user connection that does not include provision for message store-and-forward service. utilities-1. Programs used to perform a routine task. 2. Standard routines of often-used functions, usually supplied as par&of system software. utility-A (usually small) application or computer subroutine designed with a very particular task in mind, like converting between two formats. utility program- 1. A program providing basic conveniences, such as capability for loading and saving programs, for observing and changing values in a computer, and for initiating program execution. The utility program eliminates the need to rewrite a program every time a designer wants to perform a common function. 2. A computer program made available by the operating system to save programmers the bother of writing their own programs to do often-needed tasks. utility routine-A standard routine, usually part of a larger software package, that performs a service and/or program maintenance function, such as file maintenance, file storage and retrieval, media conversions, and production of memory and file printouts. utilization factor--In electrical power distribution, the ratio of the maximum demand of a system (or part of a system) to the rated capacity of the system (or part) under consideration. Utilogic-A line of digital ICs built around a basic AND and a basic NOR circuit. The AND has multiple emitter inputs; the NOR has emitter-follower inputs. The output for the AND is an emitter follower, and for the NOR, a totem-pole arrangement. A J-K binary element is also included in the line. UUT-Abbreviation for unit under test. UV erasable PROM -Abbreviation for ultraviolet erasable PROM. A programmable read-only memory that can be cleared (set to 0) by exposure to intense ultraviolet light. After being cleared, it may be reprogrammed. UVROM -An ultraviolet light erasable read-only memory. The memoIy is totally erased when exposed to ultraviolet light for a minimum of 20 minutes.

V

vacuum metalizing-A process in which surfaces V- 1. Letter symbol for volt. 2. Symbol for voltmeter. are given a thin coating of metal by exposing them to 3. Schematic symbol for vacuum tube. metallic vapor produced by evaporation under vacuum VCC-Symbol for the supply voltage to an integrated (one millionth of normal atmospheric pressure). circuit with respect to ground. vacuum phototube- 1. A phototube that is evacuVDD, VSS, VCC, V E E - I ~ an MOS circuit, the desated to such a degree that its electrical characteristics are ignation of the power-supply terminal serving the drain, essentially unaffected by gaseous ionization. 2. A photosource, collector, or emitter. The double subscript refers to tube that functions within a vacuum and therefore elimthe power-supply terminal, while a single subscript refinates the effect of gaseous ionization on its electrical erences the parameter at the element of a device. For properties. example, Vc is the voltage measured on the collector vacuum pickup-A handling instrument with a itself, while Vcc is the (constant) voltage supplied to small vacuum cup on one end, used to pick up chip the collector circuit. Note: In CMOS, the term VDDhas devices. been adopted as a convention referring to the positive vacuum range-For a communications system, the power-supply terminal, although it is actually applied to maximum range computed for an atmospheric attenuation the source of a p-channel transistor. of zero. VA--Letter symbol for voltampere. vacuum seal -An airtight junction between compovac -Abbreviation for vacuum. nent parts of an evacuated system. vaccine-A program to detect the presence of a vacuum switch-A switch in which the contacts computer virus. are enclosed in an evacuated bulb, usually to minimize vacuum -Abbreviated vac. Theoretically, an ensparking. closed space from which all air and gases have been vacuum tank-An airtight metal chamber that removed. However, since such a perfect vacuum is never contains the electrodes and in which the rectJfying action attained, the term is taken to mean a condition whereby takes place in a mercury-arc rectifier. sufficient air has been removed so that any remaining vacuum tight-See hermetic. gas will not affect the characteristics beyond an allowable vacuum tube-An electron tube evacuated to such amount. a degree that its electrical characteristics are essentially vacuum capacitor -A capacitor consisting usually unaffected by the presence of residual gas or vapor. of two concentric cylinders enclosed in a vacuum to raise vacuum-tube amplifier- An amplifier in which the breakdown voltage. electron tubes are used to control the power from the vacuum deposition-A process in which a sublocal source. stance is heated in a vacuum enclosure until the substance vacuum-tube characteristics-Data that shows vaporizes and condenses (deposits) on the surface of how a vacuum tube will operate under various electrical another material in the enclosure. This process is used in conditions. the manufacture of resistors, capacitors, microcircuits, and vacuum-tube keying -A code-transmitter keying semiconductor devices. The deposited material is called a system in which a vacuum tube is connected in series thin film. with the plate-supply lead going to the winding in the vacuum envelope-The airtight envelope that conplate circuit of the final stage. The grid of the tube is tains the electrodes of an electron tube. connected to its filament through the transmitting key so vacuum evaporation -A process in which a matethat when the key is open, the tube is blocked, interrupting rial is vaporized and the vapor deposits itself, through the plate supply to the output stage. Closing the key allows openings in a mask, onto a substrate to form a thin film. plate current once more through the keying tube and the vacuum gage-A device that indicates the absolute output tubes. gas pressure in a vacuum system (e.g., in the evacuated vacuum-tube modulator-A modulator in which parts of a mercury-arc rectifier). a vacuum tube is the modulating element. vacuum impregnation -Filling the spaces between vacuum-tube oscillator-A circuit in which a electric parts or turns of a coil with an insulating comvacuum tube is used to convert dc power into ac power pound while the coil or parts are in a vacuum. at the desired frequency. vacuum level-The degree of a vacuum, as detervacuum-tube rectifier-A tube that changes an mined by the pressure: rough vacuum (760 torr to 1 torr), alternating current to an unidirectional pulsating direct torr), high vacuum medium vacuum (1 torr to current. torr to torr), very high (hard) vacuum torr vacuum-tube transmitter-A radio transmitter in which electron tubes are utilized to convert the applied to torr), ultrahigh (ultrahard) vacuum (below electric power into radio-frequency power. torr). nnn bLL

vacuum-tube voltmeter

823

vacuum-tube voltmeter-Abbreviated VTVM. See electronic voltmeter. valence -A number representing the proportion in which an atom is able to combine with other atoms. It generally depends on the number and arrangement of electrons in the outermost shell of each type of atom. valence band- 1. In the spectrum of a solid crystal, the range of energy states containing the energies of the valence electrons that bind the crystal together. In a semiconductor material, it is just below the conduction hand, separated from it by the forbidden gap. 2. The band of atomic energy levels containing the valence electrons, i.e., those electrons in the outer shell of an atom. In an insulating or semiconductor material, the valence band energy level is below the conduction band. In a conducting material -for example, copper, aluminum, silver, gold, and lead- the valence-band energy level is above the conduction-band energy, thus allowing the electrons to be more free to move as an electric current. valence bond-Also called a bond. The bond formed between the electrons of two or more atoms. valence electrons- 1. The electrons of an atom in the outer shell that determine the chemical valency of the atom. 2. Electrons in the valence band of a semiconductor, where they are free to move under the influence of an electric field.

Yalence electrons.

valence shell-The electrons that form the outermost shell of an atom. validlate-To ensure {correctnessof data that has been (previously) or is being entered by any of a number of means, including check digit, batch total, numeric only field, and verification. validation -The process of verifying that execution of a system in its specified environment causes no operational problems. Includes prevention, diagnosis, recovery, and correction of errors. validity-Correctness; specifically, how closely repeated approximations approach the desired (i.e., correct) result. validity c h e c k - 1. A check to detennine that a code group actually represents a character in the particular code being used. 2. A computer input-data check based on known limits for variables in given fields. valley-A dip between two peaks in a curve. valley current--In a tunnel diode, the current measured at the positive voltage for which the current has a minimum value from which it will increase if the voltage is further increased.

;

-

1-1

I A

Valley current.

valley point-The point on the characteristic of a tunnel diode corresponding to the lowest voltage greater than the peak point voltage for which the differential conductance is zero. valley-point current-The current value at the valley point. valley-point emitter current -The currert flowing in the emitter of a unijunction transistor when the device is biased to the valley point. valley-point voltage -The voltage value at the valley point. valley voltage-In a tunnel diode, the voltage corresponding to the valley current. V a l U e - 1. The magnitude of a physical quantity. 2. The quantitative measure of a signal or variable. value analysis -The systematic use of techniques that serve to identify a required function, establish a value for that function, and finally to provide that function at the lowest overall cost. This approach focuses on the functions of an item rather than the methods of producing the present product design. value theory- The assignment of numerical significance to the worths of alternative choices. valve-1. A British term for a vacuum tube. 2. A device permitting current flow in one direction only (e.g., a rectifier). 3. A device or system that is capable of flow diversion, cutoff, or modulation. valve tube-See kenotron, 1. Van Allen radiation belts -Two doughnut-shaped belts of high-energy particles that surround the earth and are trapped in its magnetic field. They were first discovered by Dr. James A. Van Allen of Iowa State University. Van Atta antenna-A retrodirective array of antenna elements so interconnected that an incident wave produces a radiated beam from the array in the direction of the incident wave reversed over a significant range of angles of incidence, as in the case of an optical autocollimator. Versions of the array may contain amplifiers, circulators, and mixers, and may direct the transmitted beam, with or without modifications, in a direction or directions other than that of the incident wave reversed. Van Atta array-An antenna array designed so that the received signal is reflected back toward its source in a narrow beam to provide signal enhancement without

Van de Graaff accelerator

- variable connector

amplification. It consists of pairs of corner reflectors or other elements equidistant from the center of the array and connected together by means of low-loss transmission line. Van de Graaff accelerator -An electrostaticgenerator type of particle accelerator from which the voltage is obtained by picking up static electricity at one end of the machine (on a rubber belt) and carrying it to the other end, where it is stored.

-L

Motor

Van de Graangenerator.

vane-anode magnetron-A cavity magnetron in which the walls between adjacent cavities have parallel plane surfaces. vane attenuator-A waveguide device designed to preset attenuation in a circuit by sliding a resistive element from the side wall of the waveguide to the center for maximum attenuation. T h i s method of attenuation is used in precision calibrated attenuation readings, and resetting must be made. Some of its countless applications are calibrations of other attenuators, directional couplers, filters, and other lossy components, in antenna-pattern measurements, noise-level measurements, and for setting power levels to desired values. vane-type instrument-A measuring instrument in which the pointer is moved by the force of repulsion between fixed and movable magnetized iron vanes, or by the force between a coil and a pivoted vane-shaped piece of soft iron. vane-type magnetron-A cavity magnetron in which the walls between adjacent cavities have plane surfaces. V-antenna -A V-shaped arrangement of conductors, the two branches being fed equally in opposite phase at the apex. vapor pressure-The pressure of the vapor accumulated above a confined liquid (e.g., in a mercury-vapor rectifier tube). vaporware-A jocular term for products or components that have been announced by a vendor that do not yet exist and may never exist.

824 var -Letter symbol for voltampere reactive. The unit of reactive power, as opposed to real power in watts. One var is equal to one reactive voltampere. VAR -Abbreviation for visual-aural range, varactor -Also called varactor diode, silicon capacitor, voltage-controlled capacitor, and voltagevariable capacitor. 1. A two-terminal solid-state device that utilizes the voltagevariable capacitance of a pn junction. In the normal semiconductor diode, efforts are made to minimize inherent capacitance, while in the varactor, this capacitance is emphasized. Since the capacitance varies with the applied voltage, it is possible to amplify, multiply, and switch with this device. 2. Semiconductor diode that exhibits a change in capacitance with a change in applied voltage when operated in a reverse-biased condition. Varactors are used as voltage-variable capacitors in tuned circuits. varactor diode-A two-terminal semiconductor device in which use is made of the fact that its capacitance varies with the applied voltage. See also varactor. varactor-tuned oscillator- An oscillator in which a varactor diode is used in the frequency-determining networks that encompass the circuit’s active device@). varhour meter- Also called a reactive voltamperehour meter. An electricity meter that measures and registers the integral (usually in kilovarhours) of the reactive power of the circuit into which the meter is connected. variable-1. Any factor or condition that can be measured, altered, or controlled (e.g., temperature, pressure, flow, liquid level, humidity, weight, chemical composition, color). 2. A quantity that can take on any of a given set of values. 3. In a computer, a symbol whose numeric value changes from one iteration of a program to the next or within each iteration of a program. variable-area track- A sound track divided laterally into opaque and transparent areas. A sharp line of demarcation between these areas forms an oscillographic trace of the waveshape of the recorded signal. variable-capacitance diode -Abbreviated VCD. A semiconductor diode in which the junction capacitance present in all semiconductor diodes has been accentuated. An appreciable change in the thickness of the junctiondepletion layer and a corresponding change in the capacitance occur when the dc voltage applied to the diode is changed. variable-capacitance transducer -A transducer that measures a parameter or a change in a parameter by means of a change in capacitance. variable capacitor-1. A capacitor that can be changed in capacitance by varying the useful area of its plates, as in a rotary capacitor, or by altering the distance between them, as in some trimmer capacitors. 2. A capacitor whose capacitance can be varied by varying the separation between a pair of plates, or by varying the depth of insertion of interleaved plates. (Most widely used for tuning radio-frequency circuits.) variable-carrier modulation-See controlledcarrier modulation. variable-compression capacitor-A capacitor in which the capacitance can be varied by compressing a stack of electrode and dielectric layers. variable concentric capacitor- An air dielectric capacitor in which the capacitance can be varied by the axial movement of a rotor in a stator. variable connector- 1. A flowchart symbol representing a sequential connection that is not h e d , but which can be varied by the flowcharted procedure itself. 2. The device that inserts instructions in a program corresjmnding to the selection of paths appearing in a flowchart. 3. The computer instructions that cause a logical chain to take one of several alternative paths.

variable coupling - variable resistor

825 variable coupling --Inductive coupling that can be varied by moving the windings. varialble-cycle operaition-Computer operation in which any cycle is started at the completion of the previous cycle, instead of at specified clock times. varlalble-density track- A sound track of constant width antd usually, but not necessarily, of uniform light transmission on any instantaneous transverse axis. The average light transmission varies along the longitudinal axis in proportion to some characteristic of the applied signal. variable-depth sonair-A sensor that can be lowered by cable from a ship or helicopter, through the thermal layers, to detect submarines operating at deeper levels. variable disc capacitor-A solid-dielectric capacitor in which the capacitance can be varied by rotating a metal or metallized disc. variable-erase recording-The method of recording on magnetic tape by selective erasure of a prerecorded signal. variable field-A field in which the scalar (or vector) at any point changes during the time under consideration. variable-frequency oscillator-Abbreviated VFO, A stable oscillator whose frequency can be adjusted over a given range. warialble-frequency synthesizer -An instrument that translates the stability of a single frequency, usually obtained from a frequency standard, to any one of many other possible frequencies. In common usage, such instruments are called simply frequency synthesizers. wariable inductance-Also called variable inductor. A coil whose inductance can be varied.

START

n

\

COIL

/

COIL

FORM

variable point -Pertaining to a system of numeration in which the position of the radix point is indicated by a special character at that position. variable radio-frequencyradiosonde --A radiosonde whose carrier frequency is modulated by the magnitude of the meteorological variables being sensed. variable reluctance-Principle employed in certain phonograph pickups. Deflections of the stylus when playing a record make an armature vibrate between the poles of an electromagnet. The reluctance is the ratio of magnetic force to magnetic flux in a magnetic field. Variations due to stylus movement create variations in the current through the electromagnet. variable-reluctance microphone- Also called a magnetic microphone. A microphone that depends for its operation on the variations in reluctance of a magnetic circuit. variable-reluctance pickup-1. A phonograph cartridge that derives its electrical output signal from change effected in a magnetic circuit by means of some mechanical device such as a moving coil or magnet. 2. A type of cartridge that generates its signal from the relative motions of a magnetic field and a coil or coils (either the field or the coils may move, depending on cartridge design). The output is proportional to the velocity of the stylus motion. This requires an equalization circuit in the preamplifier to restore proper frequency balance, since records are cut with more nearly constant-amplitude than constant-velocity characteristics. 3. A phonograph pickup that depends for its operation on the variation of a resistance.

MOUNTING CLIP

OUTER COIL FORM

Variable-reluctancepickup.

A FINISH

‘CORE IUNOEA COIL)

\ ROD

varhbl8einductance.

variable-inductancepickup-A phonograph pickup in ahich the movement of a stylus causes the inductance to vary accordingly. variable-inductance transducer -A transducer in which the output voltage is a function of the change in a variable-inductance element. variable-length record-In a computer, pertaining to a file in which there is no constraint on the record length. (Opposite of fixed-length record.) variable monoergic -A type of emission in which the magnitude of the homogeneous particle or radiation energy is continuously variable over broad limits; e.g., the proton energy from some types of accelerators can be controlled by varying the high voltage. variable-mu pressure transducer- A device that converts mechanical input pressure to a proportional electrical output based on the change of the mu of its magnetic circuit due to the applied pressure (Villa~i effect). variable-mu tube --See remote-cutoff tube.

variable-reluctance stepping motor- -A motor with a soft-iron rotor that is made to step by sequential excitation of stator coils. It requires complementary equipment to furnish the sequencing pulses. variable-reluctance transducer- Also called a magnetic transducer. A transducer that depends fOF its operation on the variations in reluctance of a magnetic circuit. variable-resistance transducw -A transducer in which the signal output depends on the change in a resistance element. variable resistor -A wirewound or composition resistor whose resistance may be changed. See also potentiometer, 1; rheostat.

Variable resistors.

variable-speed motor

- vector cardiograph

variable-speed motor- A motor whose speed can be adjusted within certain limitations, regardless of load. variable-speed scanning -A scanning method whereby the optical density of the film being scanned determines the speed at which the scanning beam in the cathode-ray tube of a television camera is deflected. variable transformer- An iron-core transformer with provision for varying its output voltage over a limited range, or continuously from zero to maximum- generally by the movement of a contact arm along exposed turns of the secondary winding. variable tubular capacitor-A solid-dielectric capacitor in which the capacitance can be varied by the axial movement of an electrode within a tube. variable vane capacitor-A capacitor in which the capacitance can be varied by rotating the rotor vanes between the stator vanes. Variac -An autotransformer that contains a toroidal winding and a rotating carbon brush so that the output voltage is continuously adjustable from zero to line voltage plus 17 percent. Trade name of General Radio Company. variance-A measure of the fluctuations of data around the mean. variants- 1. Two or more cipher or code groups that have the same plain-language equivalent. 2. Two or more plaintext meanings that are represented by a single code group. variate-See random variable, 1. variation -The angular difference between a true and a magnetic bearing or heading. varicap-See varactor. varindor- An inductor whose inductance varies markedly with the current in the Winding. variocoupler-A radio transformer with windings that have an essentially constant self-impedance, but the mutual impedance between them is adjustable. variolosser- A device whose loss can be controlled by a voltage or current. variometer -A variable inductor consisting of a pair of series- or parallel-connected coils whose axes can be varied one with respect to the other. The change in mutual inductance causes a change in the total inductance. varioplex-A telegraph switching system that establishes connections on a circuit-sharing basis between a number of transmitters in one locality and corresponding receivers in another locality over one or more intervening channels. Maximum use of channel capacity is obtained by employing momentary storage of signals and allocating circuit time in rotation among the transmitters that have information in storage. varistor-From “variable resistor.” 1. A twoelectrode semiconductor device with a voltage-dependent nonlinear resistance that drops markedly as the applied voltage is increased. 2. A passive resistorlie circuit element whose resistance is a function of the current through it. The current through it is a nonlinear function of the voltage across its terminals; hence, a self-varying resistance. See aZso voltage-dependent resistor. 3. A voltage-dependent symmetrical resistor with a high degree of nonlinearity (the resistance does not change linearly as a function of the applied voltage). The value of the resistance is very high at voltages lower than nominal and very quickly changes to an extremely low value of resistance as the applied voltage is increased above the nominal voltage. The device is used as a voltage-transient or voltage-surge suppressor to improve the reliability of a voltage-sensitive circuit. It provides instantaneous response to high voltage, with good temperature stability and excellent clamping characteristics. The device is normally connected across its input terminals or across the

826 ac power source, providing protection with an effective low resistance somewhat above the normal input or line voltage values. One of the varistor’s main uses is to protect electronic equipment against lightning. It is also used to protect against sudden or transient surges of voltage in an ac power line. See also MOV. Varley loop-A type of Wheatstone-bridge circuit that gives, in one measurement, the difference in resistance between two wires of a loop. varmeter-Also called a reactive voltampere meter. An instrument for measuring reactive power in either vars, kilovars, or megavars. If the scale is graduated in kilovars or megavars, the instrument is sometimes designated a kilovarmeter or megavarmeter. varnished cambric-A linen or cotton fabric that has been impregnated with varnish or insulating oil and baked. It is used as insulation in coils and other radio parts. varying duty -A requirement of service that demands operation at loads and for intervals of time, both of which may be subject to wide variation. varying-speed motor-A motor that slows down as the load increases (e.g., a series motor, or an induction motor with a large amount of slip). varying voltage control-A form of armaturevoltage control obtained by impressing, on the armature, a voltage that varies considerably with a change in load and consequently changes the speed of the motor (e.g., by using a differentially compound-wound generator or a resistance in the armature circuit). V-beam system-A radar system for measuring elevation. The antenna emits two fan-shaped beams, one vertical and the other inclined, which intersect at ground level. Each beam rotates continuously about a vertical axis, and the time elapsing between the two echoes from the target provides a measure of its elevation. VCD -Abbreviation for variable-capacitance diode. v-chip-A semiconductor that blocks the display of violent and/or pornographic material on a TV. Transmitters have to incorporate a signal for the system to function. VCO -Abbreviation for voltage-controlled oscillator. VCR -1. Abbreviation for voltage-controlled resistor. 2. Abbreviation for videocassette recorder (or player). V-cut-A type of oscillator-crystal cut in which the major plane surfaces are not parallel to the X, Y, or 2 planes. VDR -See voltage-dependent resistor. VDT-Abbreviation for video display terminal. A CRT or gas-plasma tube display screen terminal or keyboard console that allows keyed or stored text to be viewed for manipulation or editing. VDU- 1. See video display unit. 2. Abbreviation for visual display unit. A display of data for use by human operators. Data is usually displayed as several rows of alphanumeric characters. vector-A quantity that has both magnitude and direction. Vectors commonly are represented by a line segment with a length that represents the magnitude and an orientation in space that represents the direction. See vector quantity. vector admittance-The ratio for a single sinusoidal current and potential difference in a portion of a circuit of the corresponding complex harmonic current to the corresponding complex potential difference. vector-ampere -“he unit of measurement of vector power. vector cardiograph- An instrument that measures both the magnitude and the direction of heart signals by displaying cardiograph signals on any desired set of axes, usually x, y, and z.

827

vector diagram -An arrangement of vectors showing the relationships between alternating quantities having the same frequency. vectored interrupt -1. An interrupt in a computer that carries its identity number or the address of its handler. 2. An interrupt scheme in which each interrupting device causes the operating system to branch to a different interrupt routine. This scheme is useful for a very fast interrupt response. vector field-In a given region of space, the total value of some vector quantity that has a definite value at each point of the region (e.g., the distribution of magnetic intensity in a region surrounding a currentcarrying conductor). vector function--A function that has both magnitude and direction (e.g., the magnetic intensity at a point near an electric circuit is a vector function of the current in that circuit). vector generator---That part of the display controller which draws vectors on the screen. Control codes within the display list specify whether the vector generators will move the beam in a blanked or unblanked mode. If the beam is unblanked, the vector will be drawn in a specified texture, vector impedance-The ratio for a simple sinusoidal current and potential difference in a portion of a circuit of the corresponding complex harmonic potentid difference to the corresponding complex current. vector interrupt-A term used to describe a microprocessor system in which each interrupt, both internal and external, has its own uniquely recognizable address. This enables the microprocessor to perform a set of specified operations that are preprogrammed by the user to handle each interrupt in a distinctively different manner. vector power-A vector quantity equal to the square root of the sum of the squares of the active and reactive powers. The unit is the vector-ampere. vector power factor--Ratio of the active power to the vector power. In sinusoidal quantities, it is the same as power factor. vector processing-A method for carrying out many repetitive mathematical operations with a single computer instruction. vector quantity-A quantity that has both magnitude and direction. Examples of quantities that are vectors are displacement, velocity, force, and magnetic intensity. vector refresh display-See calligraphic display. vector scan -Technique of displaying images on a screen, particularly suitable for precision drawings and animation. It is available only on special visual display units. Images are created by moving an electron beam in the CRT to any place on the screen, just as a pen is moved in any direction on paper. The positions are specified as IC and j~coordinates. vectorscope- 1. An oscilloscope with a circular time base of extreme stability (determined by the frequency of the color subcarrier). The instrument can be used to check the time delay between two signals because the phase difference at a particular frequency can be related to time difference. 2. Special synchroscope used in color TV camera and color encoder calibration. The vectorscope will graphically indicate on a CRT the absolute angles the different color signals describe in respect to a reference and to each other. These angles as read on the vectorscope represent the phase differences of the signals. vector s t r o k e display-See calligraphic display. velocimeter -A continuous-wave reflection Doppler system used to measure the radial velocity of an object.

vector diagram

- velocity pickup

velocity-A vector quantity that includes both magnitude (e.g., speed) and direction in relation to a given frame of reference. velocity error -The amount of angular displacement existing between the input and output shafts of a servomechanism when both are turning at the same speed. velocity filter -A storage-tube device that blanks all targets that do not move more than one resolution cell in less than a predetermined number of antenna scans. velocity hydrophone-A type of hydrophone in which the electric output is substantially proportional to the instantaneous particle velocity in the incident sound wave. velocity-lag error-A lag between the input and output of a device, proportional to the rate of variation of the input. velocity level-In decibels of a sound, 20 times the logarithm to the base 10of the ratio of the particle velocity of the sound to the reference particle velocity. The latter must be stated explicitly. velocity microphone-A microphone in which the electric output corresponds substantially to the instantaneous particle velocity in the impressed sound wave. It is a gradient microphone of order one, and is inherently bidirectional. velocity-modulated amplifier- Also called a velocity-variation amplifier. An amplifier in which velocity modulation is employed for amplifying radio frequencies. velocity-modulated oscillator- Also called a velocity-variation oscillator. An electron-tube structure in which the velocity of an electron stream is varied (velocity-modulated) in passing through a resonant cavity called a buncher. Energy is extracted from the bunched electron stream at a higher level in passing through a second cavity resonator called the catcher. Oscillations are sustained by coupling energy from the catcher cavity back to the buncher cavity. velocity modulation -Also called velocity variation. 1. Modification of the velocity of an electron stream by the alternate acceleration and deceleration of the electrons with a period comparable to that of the transit time in the space concerned. 2. Modulation of an electron stream by alternately accelerating and decelerating the electrons, thus grouping them into bunches. Velocity of light-A physical constant equal to 2.99796 x 10" centimeters per second. (More conveniently expressed as 186,280 statute miles per second, or 161,750 nautical miles per second, or 328 yards per microsecond.) velocity of propagation -1. The speed at which a disturbance (e.g., sound, radio, light waves) is radiated through a medium. 2. The ratio of the speed of the flow of an electric current in an insulated cabie to the speed of light, expressed in percentage. In the case of coaxial cables, this ratio is 65 to 66 percent, where the insulation is polyethylene. 3. The speed of transmission of electrical energy through a cable compared with its speed through air, expressed as a percentage of the speed in free space. Radio-frequency signals are transmitted in free space at a speed of 186,280 statute miles per second (2.99796 x 10' d s ) . Velocity of propagation is determined by the ratio of the dielectric constant of air to the square root of the dielectric constant of the insulation and is expressed in percent. 4. The speed with which a signal wave travels through a particular transmission. velocity pickup-A magnetic pickup whose output increase is a function of recorded velocity. (This differs from the ceramic pickup, whose output is a function of amplitude or deflection of the stylus.)

velocity resonance

- vertically polarized wave

velocity resonance-See phase resonance. velocity sorting -The selecting of electrons according to their velocity. velocity spectrograph-An apparatus for separating an emission of electrically charged particles into distinct streams in accordance with their speed, by means of magnetic or electric deflection. velocity transducer-A transducer that generates an output proportionate to the imparted velocities. velocity variation-See velocity modulation. velocity-variation amplifier- See velocity-modulated amplifier. velocity-variation oscillator-See velocity-modulated oscillator. Venn diagrams-Diagrams in which circles or ellipses are used to give a graphic representation of basic logic relations. Logic relations between classes, operations on classes, and the terms of the propositions are illustrated and &fined by the inclusion, exclusion, or intersection of these figures. Shading indicates empty areas, crosses indicate areas that are not empty, and blank spaces indicate areas that may be either. Named for English logician John Venn, who devised them. vent-A controlled weakness somewhere in the enclosure of an aluminum electrolytic capacitor to permit pressure relief in case of failure due to shorting or improper installation of the capacitor. vented baffle-An enclosure designed to properly couple a speaker to the air. ventilated transformer- A dry-type transformer that is so constructed that the ambient air may circulate through its enclosure to cool the transformer core and windings. venturi tube-A short tube with flaring ends and a constricted throat It is used for measuring flow velocity by measurement of the throat pressure, which decreases as the velocity increases. verification-The process of checking the results of one data transcription against those of another, both transcriptions usually involving manual operations. See also check. verifier- 1. Of computers, a device on which a record can be compared or tested for identity character by character with a retranscription or copy as it is being prepared. 2. A machine that is used to check the correctness of manually recorded data. verify-1. To check, usually with an automatic machine, one recording of data against another in order to minimize the number of human errors in the data transcription. 2. To make certain that the information being prepared for a computer is correct. vernier- 1. An auxiliary scale comprising subdivisions of the main measuring scale and, thus, permitting more accurate measurements than are possible from the main scale alone. 2. An auxiliary device used for obtaining fine adjustments. vernier capacitor-A variable capacitor placed in parallel with a larger tuning capacitor and used to provide a finer adjustment after the larger one has been set to the approximate desired position. vernier dial-A type of tuning dial used chiefly for radio equipment. Each complete rotation of its control knob moves the main shaft only a fraction of a revolution and thereby permits fine adjustment. vernitel-A precision device that makes possible the transmission of data with high accuracy over standard frequency-modulated telemetering systems. vertex-See node, 1. vertex plate-A matching plate placed at the vertex of a reflector.

828 vertical -In 45/45 recording, the signal produced by a sound arriving at the two microphones simultaneously and 180" out of phase, causing the cutting stylus to move vertically. vertical amplification-Signal gain in the circuits of an oscilloscope that produces vertical deflection on the screen. vertical-amplitude controls -See parabola controls. vertical antenna-A vertical metal tower, rod, or suspended wire that is used as a receiving andor transmitting antenna. vertical blanking-Blanking of a television picture tube during the vertical retrace. vertical-blankinginterval-The brief time between television fields required for the scanning electron gun to retrace from the bottom of the image to the top to begin scanning the next field. The interval occupies 16,667 milliseconds and occurs at the end of each 262.5 field scan lines. There are 21 usuable lines in this interval, which are devoted to 6 vertical synch pulses and 12 equalizing pulses, as well as additional horizontal pulse intervals. vertical-blanking pulse-In television, a pulse transmitted at the end of each field to cut off the cathoderay beam while it returns to the start of the next field. vertical-centeringcontrol-A control provided in a television receiver or cathode-ray oscilloscope to shift the entire image up or down on the screen. vertical compliance-The ability of a reproducing stylus to move vertically while in the reproducing position on a record. vertical-deflectionelectrodes-The pair of electrodes that move the electron beam up and down on the screen of a cathode-ray tube employing electrostatic deflection. vertical dynamic convergence- Convergence of the three electron beams at the aperture mask of a color picture tube during the scanning of each point along a vertical line at the center of the tube. vertical-field-blanking interval-See verticalblanking interval vertical field-strength diagram-A representation of the field strength at a constant distance from, and in a vertical plane passing through, an antenna. vertical frame transfer-A CCD configuration in which all charges accumulated during an integration period are rapidly moved out of the optically active area and to an identical optically shielded CCD area where the accumulation is read out at a slower pace during the next integration period. vertical-frequencyresponse-In an oscilloscope, the band of frequencies passed, with amplificationbetween specified limits, by the amplifiers that produce vertical deflection on the screen. vertical-hold control-See hold control. vertical-incidence transmission --The transmission of a radio wave vertically to the ionosphere and back. The transmission remains practically the same for a slight departure from the vertical (e.g., when the transmitter and receiver are a few kilometers apart). vertical-lateral recording-A technique of making stereo phonograph discs by recording one signal laterally, as in monophonic records, and the other vertically, as in hill-and-dale-transcriptions. vertical linearity control-A control that permits adjustment of the spacing of the horizontal lines on the upper portion of the picture to effect linear vertical reproduction of a television scene. vertically polarized wave -1. An electromagnetic wave with a vertical electric vector. 2. A linearly polarized wave with a horizontal field vector.

vertical MOS

829 vertical MOS-See VMOS. vertical polarization- 1. Transmission in which the transmitting and receiving antennas are placed in a vertical plane. so that the electrostatic field also varies in a vertical plane. 2. Transrnission of radio waves whose undulations vary vertically with respect to the earth. vertical quarter-wave stub-An antenna with a vertical portion that is electrically one quarter-wavelength Long. It is used generally with a ground plane at the base of the stub. vertical radiator -A transmitting antenna perpendicular to the earth’s surface. vertical recording -Also called hill-and-dale recording. Mechanical recording in which the groove modulation is perpendicular to the surface of the recording medium. vertical redundance-In a computer, an error condition that exists when a character fails a parity check, ie., has an even number of bits in an odd-parity system or vice versa. vertical resolution - 1. On a television test pattern, the number of horizontal wedge lines that can be clearly discerned by the eye before they merge together. 2. The number of horizontal lines that can be seen in the reproduced image of a television pattern. vertical retrace-1. The return of the electron beam from the bottom of the image to the top after each vertical sweep. 2. The return of the electron beam to the top of the picture tube screen or the pickup tube target at the completion of the field scan. vertical scanning -Scanning that proceeds in a series of vertical lines. vertical scrolling -The ability of a word processor to move vertically, a line at a time, up and down through a display page or more of text. This allows text that will not fit on a video display screen to be accessed for review or editing. Used in systems that have a display buffer (memoFj area) larger than the display screen capacity. vertical speed transducer -An instrument that furnishes an electrical output that is proportionate to the vertical speed of the aircraft or missile in which it is installed. arerticzal structured metal-oxide silicon power field-effect transistor-See VMOS power FET. vertical stylus force -See stylus force. vertical sweep-The downward movement of the scanning beam from top to bottom of the televised picture. vertical sync -The synchronizing pulses used to define tlhe end of one television field and the start of the next, occming at a rate of approximately 59.94 Hz (color) and 60 Bz (black and white). vertilcal-synchronizing pulse -Also called picture-synchronizing pulse. One of the six pulses transmitted at the end of each field in a television system. It maintains the receiver in field-by-field synchronism with the transmitter. vertical tracking-The phonograph pickup stylus motion ]path that is near vertical. Applies to hill-and-dale recordings on stereo discs. wertical tracking force -The minimum downward force at which a phonograph cartridge works without mistracking, i.e., a momentary hop by the stylus (making a raspy sound) or a jump into the next groove. high frequency- Abbreviated VHF. Fre9 band: 30 to 300MHz. Wavelength: 10 to 1

S.

large-scale intlegration-See VLSI. wery long range--A classification of ground radar sets by slant range, applied to those with a maximum range exceeding 250 miles (402 km).

- vibrating-reed meter

very low frequency-Abbreviated VLF. Frequency band: below 30 kHz. Wavelength: above 10,000 meters. very short range-Classification of ground radar sets by slant range, applied to those with a maximum range of less than 25 miles (40.2 km). vestigial -Pertaining to a remnant or remaining part. vestigial sideband -Amplitude-modulated transmission in which a portion of one sideband has been largely suppressed by a transducer having a gradual cutoff in the neighborhood of the carrier frequency.

PICTURE CARRIER

-0.25 MHZ 50 kHz

60

61

62 63 64 65 FREQUENCY IM MEGAHERTZ

65

Vestigial-sidebandtelevision channel. vestigial-sideband filter --A filter that is inserted between an AM transmitter and its transmitting antenna to suppress part of one of the sidebands. vestigial-sideband transmission -Also called asymmetric-sideband transmission. Signal transmission in which one normal sideband and the corresponding vestigial sideband are utilized. vestigial-sideband transmitter- A transmitter in which one sideband and only a portion of the other are transmitted. v/f converter-See voltage-to-frequency converter. VFO -Abbreviation for variable-frequency oscillator. VGA -Abbreviation for Video Graphics Array. A VGA monitor has a 480 x 640 display resolution and can display up to 256 colors simultaneously. A video standard for IBM PC and compatible computers. V-groove metal-oxide silicon -See VMOS. VHF- 1. Abbreviation for very high frequency. 2. In television, a term used to designate channels 2 through 13. VHF omnirange -Abbreviated VOR. -A specific type of range operating at VHF and providing radial lines of position in a direction determined by the bearing selection within the receiving equipment. A nondirectional reference modulation is emitted, along with a rotation pattern that develops a variable modulation of the same frequency as the reference modulation. Lines of position are determined by comparing the phase of the variable with that of the reference. VHLL -Abbreviation for very high-level language. Usually a problem or requirements description language, ranging in form from the highly abstract to plain English. VHSIC -Abbreviation for very high-speed integrated circuits. via -1. A vertical conductor or conductive path forming the interconnection between multilayer hybrid circuit layers. 2. Means of passing from one layer or side of a printed circuit board to the other. via hole-A plated-through hole that establishes electrical continuity but which is not intended for a component lead. See plated-through hole. vibrating bell --A bell having a mechanism designed to strike repeatedly and as long as it is actuated. vibrating-reed meter -Also called reed frequency meter. A frequency meter consisting of a row of steel

vibrating-reed relay

- videocassette recorder

reeds, each having a different natural frequency. All are excited by an electromagnet fed with the alternating current whose frequency is to be measured. The reed whose frequency corresponds most nearly with that of the current vibrates, and the frequency is read on a scale beside the row of reeds. vibrating-reed relay-1. A type of relay in which an alternating or a self-intempted voltage is applied to the driving coil so as to produce an alternating or pulsating magnetic field that causes a reed to vibrate. 2. A type of relay that is actuated by sound frequency. Can be triggered by an electrical resonant circuit, or simply by a mechanically induced sound vibration. vibrating-wire tranducer-A transducer that utilizes a thin wire suspended in a magnetic field; the change in tension of the wire reflects a frequency-modulating output. vibration-1. A continuously reversing change in the magnitude of a given force. 2. A mechanical oscillation or motion about a reference point of equilibrium. vibration analyzer-A device used to analyze mechanical vibrations. vibration-detection system- An alarm system that employs one or more contact microphones or vibration sensors that are fastened to the surfaces of the area or object being protected to detect excessive levels of vibration. The contact microphone system consists of microphones, a control unit containing an amplifier and an accumulator, and a power supply. The unit’s sensitivity is adjustable so that ambient noises or normal vibrations will not initiate an alarm signal. In the vibration sensor system, the sensor responds to excessive vibration by opening a switch in a closed-circuit system. vibration galvanometer- An ac galvanometer in which a reading is obtained by making the natural oscillation frequency of the moving element equal to the frequency of the current being measured. vibration isolator-A resilient support that tends to isolate a system from steady-state excitation or vibration. vibration meter -Also called a vibrometer. An apparatus comprising a vibration pickup, calibrated amplifier, and output meter, for the measurement of displacement, velocity, and acceleration of a vibrating body. vibration pickup-A microphone that responds to mechanical vibrations rather than to sound waves. In one type, a piezoelectric unit is employed; the twisting or bending of a Rochelle-salt crystal generates a voltage that varies with the vibration being analyzed. vibration sensitivity-The peak instantaneous change in output at a given sinusoidal vibration level for any one stimulus value within the range of an instnunent or equipment. It is usually expressed in percentage of full-scale output per vibratory “g” over a given frequency range. It may also be specified as a total error in percentage of full-scale output for a given vibratory acceleration level. vibration sensor-A sensor that responds to vibrations of the surface on which it is mounted. It has a normally closed switch that will momentarily open when it is subjected to a vibration with sufficiently large amplitude. Its sensitivity is adjustable to allow for the different levels of normal vibration, to which the sensor should not respond, at different locations. See also vibrationdetection system. vibration survey-A method of determining the natural frequency of a transducer by observation of the output waveform upon the application of a shock or tapping of sufficient magnitude to initiate oscillation of the instrument.

830 vibration &&-A test to determine the ability of a device to withstand physical oscillations of specified frequency, duration, and magnitude. vibration welding-Method of fusing two plastic parts by vibrating (rubbing) the mating surfaces together at relatively low frequencies, 90 to 120 Hz. vibrato -1. A musical embellishment that depends primarily on periodic variations of frequency, often accompanied by variations in amplitude and waveform. The quantitative description of vibrato is usually in terms of the corresponding modulation of frequency (typically 5 to 7 Hz), amplitude, or waveform, or all three. 2. Regular variation in the frequency of a sound, generally at a frequency between 2 and 15 times per second. This frequency modulation by a low-frequency oscillator is commonly used with guitars, organs, synthesizers, and the human voice. vibrator- 1. A vibrating reed that is driven like a buzzer and has contacts arranged to interrupt direct current to the winding(s) of a transformer, resulting in an alternating current being supplied from another winding to the load. 2. Electromagnetic device that is used to change a continuous steady current into a pulsating current. 3. An electromagnetic device for converting a direct voltage into an alternating voltage. vibrator power supply-A power supply incorporating a vibrator, step-up transformer, rectifier, and filters for changing a low dc voltage to a high dc voltage. vibratron-A triode with an anode that can be moved or vibrated by an external force. Thus, the anode current will vary in proportion to the amplitude and frequency of the applied force. vibrometer-See vibration meter. video -1. Pertaining to the bandwidth and spectnun position of the signal resulting from radar or television scanning. In current usage, video means a bandwidth on the order of several megahertz and a spectrum position that goes with a dc carrier. 2. A prefix to the name of television parts or circuits that carry picture signals. 3. Radar or television signals that actuate a cathode-ray tube. 4. Composite video contains color and luminance (brightness information) as well as horizontal and vertical synch pulses during the horizontal and vertical blanking intervals. One line of video, for instance, amounts to approximately 52 microseconds in visible horizontal scan time, and 63.5 microseconds for a complete line, including the color burst and horizontal synch. video adapter- An expansion board in a computer that provides enhanced display capabilities. video amplifier- 1. An amplifier that provides wideband operation in the frequency range of approximately 15 hertz to approximately 5 megahertz. 2. An amplifier designed for linear amplification over a wide range of frequencies from dc (zero) to over about 10 MHz. 3. A wideband amplifier used for passing picture signals. video band-The frequency band utilized to transmit a composite video signal. video carrier- 1. The television signal whose modulation sidebands contain the picture, sync, and blanking signals. 2. A frequency that is 1.25 MHz above the lower edge of the assigned 6-MHz frequency band of a TV channel. At channel 2, for instance, with a bandwidth of 54 to 60 MHz, the video carrier rests at 55.25 MHZ. videocassette-A plastic shell containing two reels and a given length of videotape. videocassette recorder- Abbreviated VCR. A device for recording and playing video images on magnetic tapes that are contained in plastic cases.

videocast

a3 1 VIDEO HEADS

HEADWHEEL

Vieocass8etterecorder. videocast- 1. To broadcast a program by means of television. 2. A program so broadcast. VideoCipher I, Il--Pi trademark for a video/audio encryption system developed by MIA-COM LINKABIT, Inc. VCI uses digital video and audio encryption; VCII uses analog video and digital audio encryption. video compression-1. The reduction of the number of bits needed to describe a video image. 2. A digital technique to compress several video channels into the bandwidth normally required by one channel. videai correlator-A radar circuit that enhances the capability for automatic target detection; supplies data for digital target plotting; and provides improved immunity to noise, interference, and jamming. video data digital processing -Digital processing of video signals for pictures transmitted by way of a television link. A computer is used to compare each scanned line with adjacent lines so that extreme changes resulting from electromagnetic interference can be eliminated. video detector -The demodulator circuit that extracts the picture information from the amplitudemodulated intermediate frequency in a television receiver. video dialtone-An FCC term for the new generation of home-distribution video systems that deliver compressed digital signals over switched networks to an interactive set-top box in the user premises. video digitizing-Thme process of capturing, converting, and storing video images for use by a computer. video disc-see optical video disc. video discrimination -A radar circuit that reduces the frequency band of the video-amplifier stage in which it is used. video display unit-Abbreviated VDU. A device for visual presentation of ~mnformation.A CRT is a typical video display unit. video freeze-A TV mode which makes it possible to “freeze” an image to study specific details at ease, e.g., to make notes of certain program information like phone numbers. video frequency- 1. The frequency of the signal voltage containing the piclue information that arises from the television scanning process. In the present United States television system, these frequencies are limited from approximately 30 Hz to 4 MHz. 2. A band of frequencies extending from less than 100 hertz to several megahertz. video-frequency amplifier--A device capable of amplifying those signals that comprise the periodic visual presentation. video-gain control-A control for adjusting the amplitude of a video signal. Two such controls are provided in the matrix section of some color television

- videotape recorder

receivers so that the proper ratios between the amplitudes of the three color signals can be obtained. video impedance--Of a detector diode, the output impedance measured at the video frequency when the diode is operating under specified bias conditions. video integration-A method of improving the output signal-to-noise ratio by utilizing the redundancy of repetitive signals to sum the successive video signals. video integrator-A device that uses the redundance of repetitive signals to improve the output signalto-noise ratio by summing the successive video signals. video inversion-A type of encoding or scrambling in which the transmitted downlink video signals are inverted. video mapping-The procedure whereby a chart of an area is electronically superimposed on a radar display. video masking-A method for the removal of chaff echoes and other extended clutter from radar displays. video mixer-A circuit or device used to combine the signals from two or more television cameras. video moir6-See moire effect. video monitor-A high-quality television set (without rf circuits) that accepts video baseband inputs directly from a TV camera, VTR, or satellite TV receiver with no rf modulator required. video pair cable-A transmission cable containing low-loss pairs with an impedance of 125 ohms. Used for TV pickups, closed circuit TV, telephone carrier circuits, etc. video recording (magnetic tape) --The methods of recording data having a bandwidth in excess of 100 kHz on a single track. video signal -1. The picture signal in a television system-generally applied to the signal itself and the required synchronizing and equalizing pulses. 2. In television, the signal that conveys all of the intelligence present in the image, together with the necessary synchronizing and equalizing pulses. 3. That portion of the composite video signal that varies in gray-scale levels between reference white and reference black. Also referred to as the picture signal, this is the portion that can be seen. 4. The picture signal. A signal containing visud information and horizontal and vertical blanking. See also composite video signal. 5 . The output from a video graphics adapter incorporating the red (R), green (G), and blue (B) signals and the luminance signal, or combinations of these signals, that pass to the video input of a monitor. video stretching-In navigation, a procedure whereby the duration of a video pulse is increased. video synthesizer -A video analog computer that accepts standard video signals from a camera, film chain, videotape or graphics generator, which it then processes and applies a combination of effects to in order to reshape and add motions (animation) to fixed graphics or live scenes. videotape-A wide magnetic tape designed for recording and playing back a composite black and white or color television signal. videotape recorder- Abbreviated VTR. 1. A device that permits audio and video signals to be recorded on magnetic tape and then played back without any processing, as with films, on a CCTV monitor. 2. A device that translates the electrical signals of a VTR television camera into corresponding magnetic variations, which are recorded on magnetic tape; the original image can be displayed on a television receiver at a later time by reconversion of the magnetic variations, stored on the tape, into appropriate electrical signals.

videotape recording

- viscometer

v i d e o t a p e recording -Abbreviated VTR. A method of recording television picture and sound signals on tape for reproduction at some later time. videotex- 1. A system that links TV screens to mass databases through television or telephone-based communication channels. 2. A generic term for interactive services delivered to personal computers or adapted television sets in the home or office. 3. Technology that connects computerized text and graphics to a television screen via telephone lines. 4. A terminal-oriented communication network that links users’ equipment to a computer that maintains a database of information services. Videotex services include shop-at-home catalogs, listings of community events, and message forwarding. videotext system -A system for the widespread dissemination of textual and graphic information by wholly electronic means for display on low-cost terminals (often suitably equipped television receivers) under the selective control of the recipient using control procedures easily understood by untrained users. vidicon- 1. A camera tube in which a charge-density pattern is formed by photoconduction and stored on that surface of the photoconductor which is scanned by an electron beam, usually of low-velocity electrons. 2. A vacuum tube capable of changing light images into electrical voltage variations corresponding to the brightness of those images; a particular type of cathoderay pickup tube used in some video cameras. viewer- A software application that permits visual display of content. See also browser; player. viewfinder -An auxiliary optical or electronic device attached to a television camera so the operator can see the scene as the camera sees it. viewfinder monitor -See electronic viewfinder. viewing angle-The angle through which an LCD display has acceptable contrast. viewing area-The area of the CRT face that can be directly seen by the user. Its size is determined by the size of the CRT and the area covered by the face mask. viewing mirror-A mirror used in some television receivers to reflect the image formed on the screen of the picture tube at an angle convenient to the viewer. viewing screen-The face of a cathode-ray tube on which the image is produced. viewing time-The time during which a storage tube presents a visible output that corresponds to the stored information. Villari effect-A phenomenon in which a change in magnetic induction occurs when a mechanical stress is applied along a specified direction to a magnetic material having magnetostrictive properties. vinyl resin-A soft plastic used for making phongraph records. virgin tape-See raw tape. virtual address-In a computer, an immediate, or real-time, address. virtual cathode-An electron cloud that forms around the outer grid in a thermionic vacuum tube when the inner grid is maintained slightly more positive than the cathode. virtual circuit-In packet switching, a network facility that gives the appearance to the user of an actual end-to-end circuit; a dynamically variable network connection in which sequential data packets may be routed differently during the come of a virtual connection. Virtual circuits enable transmission facilities to be shared by many users simultaneously. virtual connection -A packet-switched data path betyeen two terminals that performs as if the two devices were linked by a switched circuit.

832

virtual height-1. The height of the equivalent reflection point that will cause a wave to travel to the ionosphere and back in the same time required for an actual reflection. In determining the virtual height, the wave is assumed to travel at uniform speed and the height is determined by the time required to go to the ionosphere and back at the assumed velocity of light. 2. The apparent height of a layer of the ionosphere. It is determined from the time interval between the transmitted signals and the ionospheric echo at vertical incidence (the radio wave penetrating the ionosphere perpendicular to it). virtual image-The optical counterpart of an object, formed at imaginary focuses by prolongations of light rays (e.g., the image that appears to be behind an ordinary mirror). virtual memory- 1. The use of techniques by which the computer programmer may use the memory as though the main memory and mass memory were available simultaneously. 2. A technique that permits the user to treat secondary (disk) storage as an extension of core memory, thus giving the virtual appearance of a larger core memory to the programmer. 3. A technique for managing a limited amount of high-speed memory and a (generally) much larger amount of lower-speed memory in such a way that the distinction is largely transparent to a computer user. The technique entails some means of swapping segments of program and data from the lowerspeed memory (which would commonly be a drum or disk) into the high-speed memory, where it would be interpreted as instructions or operated on as data. The unit of program or data swapped back and forth is called a page. The high-speed memory from which instructions are executed is real memory, while the lower-speed memory (drums or disks) is called virtual memory. 4. Any of several schemes in which the user-visible address space is divided into several subspaces, so that each of the subspaces in use can be placed anywhere in main memory. In some schemes, parts of the virtual memory may be on a mass-storage device. virtual PPI r e f l e c t o s c o p e -A device for superimposing a virtual image of a chart onto the PPI pattern. The chart is usually prepared with white lines on a black background to the scale of the PPI range scale. virtual reality- Abbreviated VR. 1. A technology that is computer generated and allows the user to interact with data that gives the appearance of a three-dimensional environment. The user can enter and navigate the 3D world portrayed as graphic images, and change viewpoints and interact with objects in that world as if inside that world. A virtual reality environment can be experienced using a headset and electronic gloves, or simply viewed on a monitor. 2. Sophisticated, multidimensional imaging systems and high-speed processing capabilities that create environments that users can interact with and manipulate directly. virtual storage-Storage space that may be viewed as addressable main storage, but is actually auxiliary storage (usually peripheral mass storage) mapped into read addresses; the amount of virtual storage is l i i t e d by the addressing scheme of the computer. virus- 1. A software program that attaches itself to another program in computer memory or on a disk, and spreads from one program to another. Viruses may damage data, cause the computer to crash, display messages, or lie dormant. 2. Any destructive self-replicating program. 3. A computer program written to secretly reproduce itself across many computer systems. V i s e s can cause serious software damage. viscometer- Also called a viscosimeter. A device for measuring the degree to which a liquid resists a change in shape.

833 viscosimeter -See viscometer. viscosity- 1. The frictional resistance offered by one part tor layer of a liquid as it moves past an adjacent part or layer of the same liquid. 2. The property of a liquid that resiists internal flow; measured in units of poise or centipoise. Low-viscosity materials are usually thin, while high-viscosity materials are thick. viscous and magnetic damping -Damping by virtue of the viscosity of a fluid around the sensing element or of a magnetic field. wiscous-dampened arm -A phonograph pickup a m mounted on a liquid cushion of oil, which provides high damping to eliminate arm resonances. It also protects the record groove and stylus; the arm does not fall on the record when dropped, but floats down gently. visibility factor- Also called display loss. Ratio of the minimum input-signal power detectable by ideal instruments connected to the output of a receiver to the minimum signal power detectable by a human operator through a display connected to the same receiver. The visibility factor may include the scanning loss. visible emission -Also called visible light. Radiation that is characterized by wavelengths of about 0.38 to 0.77 micrometer. visible light --Electromagnetic wavelengths that can be seen by the human eye, ranging from 380 to 770 nanometers. visible radiation-Radiation with wavelengths ranging from about 0.4 and 0.7 micrometer, corresponding to the visible spectrum of light. visible spectrum--That region of the electromagnetic spectrum to which the retina is sensitive and by which the eye sees. It extends from about 400 to about 750 nanometers in wavelengths of the radiation. v i s h - T h e series of processes in which luminous energy incident on the eye is perceived and evaluated. visual-aural range-Abbreviated VAR. A special type of VNF range providing a pair of radial lines of position that are reciprocal in bearing and are displayed to the pilot on a zero-center, left-right indicator. This facility also provides a pair of reciiprocal radial lines of position located 90" from the above visually indicated lines. These are presented to the pilot as aural A-N radio-range signals, which provide a means for differentiating between the two visually indicated lines (and vice versa). visuall carrier frequency -The frequency of the television carrier that is modulated by the picture information. aU communication -Communication by optical signs such as flags and lights. visualiization-Graphic representation of abstract data usually relayed in texl, and numbers. visual radio range--Abbreviated VRR. A radio range whose course is fiollowed by means of visual instruments. visuall scanner- I. A device that generates an analog OIC digital signal by optically scanning printed or written data. 2. See scanner, 2. visual signal device -A pilot light, annunciator, or other device that provides a visual indication of the iconditioni of the circuit or system being supervised. visual storage tube--An electron tube that stores and visually displays infomation by means of a cathoderay beam scanning and charge storage mechanism. visual telephony -The transmission of picture information (television) by means of telephone lines. visual transmitter- Also called a picture transmitter. In tel~evision,the radio equipment for transmission of the picture signals only.

visual transmitter power- The peak power output during transmission of a standard television signal. vitreous -1. Having the nature of glass. 2. A term used in ceramic technology to indicate fired characteristics approaching being glassy, but not necessarily totally glassy. vitreous binder-A glassy material used in compounds to bind other particles together. This takes place after melting the glass and cooling. vitrification- 1. The progressive reduction in porosity of a ceramic m a t e d as a result of heat treatment or some other process. 2. The reduction of porosity in a ceramic product through the formation of a glassy bond. VLF -Abbreviation for very low frequency. VLSl -Abbreviation for very large-scale integration. Generally considered to be an IC with more than 1000 gates. VLsl circuit- Abbreviation for very large-scale integrated circuit. See gate array, 3. VMOS -1. Abbreviation for V-groove metal-oxide silicon -a variation of MOS technology. A manufacturing process (called isotropically etched double-diffusion MOS process) based on the technique of using V-shaped grooves in the silicon wafer to provide a third-dimensional surface. This allows for a smaller chip geometry than the (older) process using a two-dimensional area technique of manufacture. With smaller geometry, the same diameter wafer can, theoretically, yield more chips (roughly 50 percent more) and thereby reduce the unit cost per chip considerably. The cost of processing a wafer generally remains constant no matter how many chips it contains. 2. Abbreviation for vertical MOS. A semiconductor device in which current travels vertically in the semiconductor chip. A cross section shows a four-layer diffusion consisting of n+ at the top (source), p as the channel, n- as the drift region, and n+ as the drain. The layers' dimensions are precisely controlled by diffusion processes. Unlike conventional bipolar transistors, VMOS devices exhibit high density because of their short channel spacing: 1 pn compared with bipolar devices typical 5 P.

SOURCE GATE

SOURCE

90,

H

EPITAXIAL

DRAIN

Structure

Symbol.

VMOS transistor.

VMOS power FET

- void

VMOS power FET- Abbreviation for vertical structured metal-oxide silicon power field-effect transistor. In these semiconductor devices, current flows vertically from source to drain. This structure results in high current densities, low saturation resistance, excellent heat dissipation and power handling capabilities, low chip capacitance, and excellent wideband performance. vocabulary-A list of operating codes or instructions available for writing the program for a given problem and for a specific computer. vocoder -Abbreviation for voice-operated coder. A device used to compress the frequency bandwidth requirement of voice communications. It consists of an electronic speech analyzer, which converts the speech waveform to several simultaneous analog signals, and an electronic speech synthesizer, which produces artificial sounds in accordance with analog control voltages. vodas -Abbreviation for voice-operated device, antising. A system for preventing the overall voice-frequency singing of a two-way telephone circuit by disabling one direction of transmission at all times. voder -Abbreviation for voice-operation demonstrator. An electronic device capable of artificially producing voice sounds. It uses active devices in connection with electrical filters controlled through a keyboard. vogad -Abbreviation for voice-operated gain-adjusting device. A voice-operated device used to give a substantially constant volume output for a wide range of inputs. voice activated (sound activated)-Refers to a bug that radiates radio frequencies or a recorder that is activated only when sound is present in target area. voice analyzer- An electronic instrument for printing out waveforms corresponding to vocal characteristics; an aid in identifying speech problems as well as speakers. voice channel -A transmission path suitable for carrying analog voice signals (covering a frequency band of 250 to 3400 Hz) between two points. voice coder-A device that converts a speech signal into digital form prior to encipherment for secure transmission, and converts the digital signals back into speech at the receiving point. voice coil-Also called a speaker voice coil. 1. A coil attached to the diaphragm of a dynamic speaker and moved through the air gap between the pole pieces. 2. The moving coil in a dynamic speaker. It is suspended in the field of a permanent magnet and is fixed to the speaker diaphragm. voice/data system -An integrated communications system for transmission of both voice and digital data signals. voice filter -A parallel-resonant circuit connected in series with a line feeding several speakers. Its purpose is to remove the tubbiness of the male voice. The frequency of resonance is adjusted somewhere between 125 and 300 Hz. voice frequency-Also called speech frequency. 1. Any of the frequencies within the band of 32 to 16,000 Hz that are audible to the human ear. 2. Any of the frequencies within the band of 300 to 3500 Hz that are normally used for telephone communication. voice-frequency carrier telegraphy-Carrier telegraphy in which the carrier currents have frequencies such that the modulated currents may be transmitted over a voice-frequency telephone channel. VOiCe-freqUeflCy dialing -A method of dialing by which the direct-current pulses from the dial are transformed into voice-frequency alternating-current pulses.

834 voice-frequency telegraph system - A telegraph system by which many channels can be carried on a single circuit. A different audio frequency is used for each channel and is keyed in the conventional manner. Each frequency is generated by an oscillator. At the receiving end, the various audio frequencies are separated by filter circuits and are fed to their respective receiving circuits. voice-frequencytelephony -Telephony in which the frequencies of the components of the transmitted electric waves are substantially the same as the frequencies of corresponding components of the actuating acoustical waves. voice grade -A telephone circuit suitable for transmitting a bandpass from 300 to approximately 2700 Hz, or greater, with certain standards of noise and interference such that intelligible speech can be transmitted. voice-grade channel-1. A channel suitable for the transmission of speech, digital or analog data, or facsimile, generally with a frequency range of about 300 to 3000 hertz. 2. A telephone circuit normally used for speech communication, accommodating frequencies from 300 to 3000 Hz. voice-grade circuit-A switched (dial-up) or leased (dedicated) telephone circuit suitable for the transmission of speech, digital or analog data, or facsimile. generally with a frequency range of about 300 to 3000 hertz. voice-grade line -A local telephone loop, or trunk, having a bandpass of approximately 300 to 3000 Hz. voice mail-Sophisticated telephone voice messages that are recorded and translated into digital bits for storage and manipulation. Voice mail systems use specialized hardware and software and can be incorporated into a PBX or used as stand-alone systems. voice-operated coder-See vocoder. voice-operated device-A device that permits the presence of voice or sound signals to affect a desired control. voice-operated device, antising - A system for preventing the overall voice-frequency singing of a twoway telephone circuit by disabling one direction of transmission at all times. Acronym: vodas. voice-operated gain-adjusting device-A voice-operated device used to give a substantially constant-volume output for a wide range of inputs. voice-operated loss control and suppressor-A voice-operated device that switches the loss out of the transmitting branch and inserts the loss into the receiving branch under control of the subscriber’s speech. voiceprint-A speech spectrograph sufficiently sensitive and detailed to identify individual human voices. Voice recognition-The conversion of spoken words into computer text. Speech is first digitized and then matched against a dictionary of coded waveforms. The matches are then converted into text as if the words were typed on the keyboard. voice-recognition equipment vocabulary size -The number of utterances (words or short phrases) that can be distinctly recognized and digitally encoded. The larger the vocabulary, the more complex the source data that can be handled without special software. voice spectrum -The total fundamental frequency range of the human voice. voice synthesis-Technology that produces sound or voices by processing compressed digital signals and storing them in a memory in the same manner a human voice generates sound processed by the vocal tract and other organs. void -The absence of substance in a localized area.

83.5 volatile-1, A computer storage medium in which information cannot be retained without continuous power dissipation. 2. Capable of evaporating. volatile memory- 1. In computers, any memory that can return information only as long as energizing power is applied. The opposite of nonvolatile memory. 2. A readwrite memory whose content is irretrievably lost when operating power is removed. Virtually all types of readlwrite semiconductor rnemories are volatile. See also nonvolatile memory. volatile storage- 1. A computer storage device in which the stored information is lost when the power is removed. 2. A storage medium in which data cannot be retained without continuous power dissipation (e.g., acoustic delay lines, electrostatics, capacitors). volatile store-A storage device in which stored data is lost when the applied power is removed (e.g., an acoustic delay line). woiatility-With respect to memory, an inability to retain stored data in the absence of external power. Voldilcon-The trade name of Adage, Inc., for a family of high-speed, all-semiconductor, current-balancing devices that use digital logic and readout for high-speed precision measurement of analog signals. volt-Letter symbol: V. 1. The unit of measurement of electromotive force. It is the difference of potential required to make a current of 1 ampere flow through a resistance of 1 ohm. 2. The difference of electric potential between two points of a conductor carrying a constant current of 1 ampere when the power dissipated between these points is equal to 1 watt. Volta effect-See contact potential. voltage- 1. Electrical pressure; Le., the force that causes current through m electrical conductor. 2. Symbolized by E. The greatest effective difference of potential between any two conductors of a circuit. 3. The term most often used in place of electromotive force, potential, potential difference, or voltage drop, to designak electric pressure that exists between two points and is capable of producing a flow of current when a closed\ circuit is connected between the two points. 4. Standard unit of magnitude of an electrical signal, named after Count A. Volta, inventor of the battery about 1800. woltage amplification -Also called voltage gain. E. Ratio of the voltage across a specified load impedance connected to a transducer to the voltage across the input of the transducer. 2. The ratio of the voltage at the input of a device to Uhe voltage at the output from the device, expressed in decibels. voltage amplifier- An amplifier used specifically to increase a voltage. It is usually capable of delivering only a small current. voltage-amplifier tube -A tube that is designed primarily as a voltage amplifier. It has high gain, but delivers very little output power. voltage and power idirectional relay-A device that pennits or causes the connection of two circuits when the voltage difference between them exceeds a given value in a predetermined direction, and causes these two circuits to be disconnected from each other when the power flowing between them exceeds a given value in the opposite direction. voltage attenuation -Ratio of the voltage across the input of a transducer to the voltage delivered to a specified load impedance connected to the transducer. voltage balance relay-A device that operates on a given difference in voltage between two circuits.

volatile - voltage-controlled oscillator voltage breakdown -1. The voltage necessary to cause insulation failure. 2. A rapid increase of current flow, from a relatively low value to a relatively high value, upon the application of a voltage to a pn junction or dielectric. voltage-breakdown test-A test whereby a specified voltage is applied between given points in a device to ascertain that no breakdown will occur at that specified voltage. voltage calibrator -Test equipment that supplies accurate ac voltages for comparison on a scope screen with other waveforms to determine their voltage level. voltage coefficient of capacitance-Also called voltage sensitivity. The quotient of the derivative with respect to voltage of a capacitance characteristic at a point divided by the capacitance at that point. voltage coefficient of resistivity-The maximum change in nominal resistance value due to the application of a voltage across a resistor, after correcting for self-heating effects; usually expressed in percent or per-unit (ppm) change in nominal resistance per volt applied. voltage comparator- 1. An amplifying device with a differential input that will provide an output polarity reversal when one input signal exceeds the other. When operating with open loop and without phase compensation, operational amplifiers make fast and accurate voltage comparators. 2. A circuit that compares two analog voltages and develops a logic output when the voltages being compared are equal or one is greater or less than the reference level. voltage control-A method of varying the magnitude of voltage in a circuit by means of amplitude control, phase control, or both. voltage-controlled capacitor -See vmactor. voltage-controlled crystal oscillator- A crystal oscillator whose operating frequency can be changed by applying a controlling voltage to introduce a phase shift in the oscillator circuit. voltage-controlled oscillator-Abbreviated VCQ. 1. Any oscillator for which a change in tuning voltage results in a predetermined change in output frequency. Frequency tuning is accomplished by either changing the bias voltage on a varactor diode in the frequencydetermining resonant network or the bias voltage to the active device. The former approach, although more complex than the latter method of tuning, is capable of multioctave bandwidth. 2. A circuit that creates an ac output signal whose frequency is a function of the dc input voltage. 3. An oscillator whose frequency can be changed by means of an external control voltage. It is commonly found in synthesizers.

Voltage-controlled oscillator.

voltage-controlled resistor

- voltage gradient

voltage-controlled resistor -Abbreviated VCR. A three-terminal variable resistor in which the resistance value between two of the terminals is controlled by a voltage potential applied to the third. voltage corrector-An active source of regulated power placed in series with the output of an unregulated supply. The voltage corrector senses changes in the output voltage (or current) and corrects for these changes automatically by varying its own output in the opposite direction so as to maintain the total output voltage constant. voltage/current crossover-The characteristic of a power supply that automatically converts the mode of operation of a power supply from voltage regulation to current regulation (or vice versa) as required by preset limits. The constant-current and constant-voltage settings are independently adjustable over specified limits. The region near the intersection of the constant-voltage and constant-current curves is designated by the term “crossover characteristics.” voltage-dependent resistor -Abbreviated VDR. Also called varistor or metal oxide varistor (MOV). A special type of resistor whose resistance changes appreciably, nonlinearly, and consistently in response to voltage across its terminals. voltage-directional relay-1. A relay that functions in conformance with the direction of an applied voltage. 2. A device that operates when the voltage across an open circuit breaker or contactor exceeds a given value in a given direction. voltage divider- Also called a potential divider. 1. A resistor or reactor connected across a voltage and tapped to make a fixed or variable fraction of the applied voltage available. See also potentiometer, 1; rheostat. 2. High-voltage resistance string, tapped resistor, potentiometer, adjustable resistors, or a series arrangement of two or more fixed resistors connected across a voltage source. Of the total voltage, a desired fraction is obtained from the intermediate tap, movable contact, or resistor junction.

I INPUT VOLTAGE

OUTPUT VOLTAGE

836

voltage drop -1. The difference in voltage between two points due to the loss of electrical pressure as a current flows through an impedance. 2. The voltage developed across the component or conductor by current through the resistance or impedance of that component or conductor. 3. The voltage developed between the terminals of a circuit component by current through the resistance or impedance of that part. See IR drop. 4. The decrease in voltage as a current traverses a resistance. 5. The voltage measured across a resistance through which a current is flowing. 6. The voltage existing across each element of a series circuit. (Also true of a contact in series with its load where a voltage drop also exists.) The voltage present across the load will be the line voltage less the voltage drops across each element in series with the load. voltage endurance -See corona resistance. voltage f e e d -Excitation of a transmitting antenna by applying voltage at a point of maximum potential (at a voltage loop or antinode).

/

- - \

I1

VOLTAGE

\

\

FEED LINE

ENDFED

/

VOLTAGE

‘.-- - -

1 1 [i!

Voltage feed.

voltage feedback-A form of amplifier feedback in which the voltage drop across part of the load impedance is put in series with the input-signal voltage.

Voltage divider.

voltage doubler -A voltage multiplier that rectifies each half cycle of the applied alternating voltage separately, and then adds the two rectified voltages to produce a direct voltage having approximately twice the peak amplitude of the applied alternating voltage.

VOLTS

DC =

2 x PEAK VOLTS AC

Voltage doubler.

Voltagefollower.

voltage f r e q u e n c y converter-A circuit that produces an output frequency that varies with the voltage applied to its input. voltage gain -See voltage amplification. voltage generator-A two-terminal circuit element with a terminal voltage independent of the current through the element. voltage gradient-The voltage per unit length along a resistor or other conductive path.

voltage inverter - voltage-regulator diode

837 voltage inverter-A circuit having a response (output) proportional to a constant (the gain) times the input signal, but opposite in sign to it. In a unity-gain inverter, the output is -1 times the input. voltage jump- An abrupt change or discontinuity in the tube voltage drop during operation of glow-discharge tubes. voltage level-Ratio of the voltage at any point in a transmission system to an arbitrary value of voltage used as a reference. In television and other systems where waveshapes are not sinusoidal or symmetrical about a zero axis and where the sum of the maximum positive and negative excursions of the wave is important in system performance, the two voltages are given as peak-to-peak values. This ratio is usually expressed in dBV, signifying decibels referred to 1 volt peak-topeak. voltage limit-A control function that maintains a voltage between predetermined values. voltage loop-A point of maximum voltage in a stationary-wave system. A voltage loop exists at the ends of a half-wave antenna. voltage loss-The voltage between the terminals of a current-measuring instrument when the applied current has a magnitude corresponding to nominal endscale deflection. In other instruments, the voltage loss is the voltage between the terminals at rated current. voltage-measuring equipment-Equipment for measuring the magnitude of an alternating or direct voltage. voltage multiplier-- 1. A rectifying circuit that produces a direct voltage: approximately equal to an integral multiple of the peak amplitude of the applied alternating voltage. 2. A series arrangement of capacitors charged by rapidly rotating brushes in sequence, giving a high direct voltage equal to the source voltage multiplied by the number of capacitors in series. 3. A precision resistor used in series with a voltmeter to extend its measuring range.

R 0

8

-0

Voltage multiplier.

voltage node-1. A point having zero voltage in a stationary-wave system (e.g., at the center of a half-wavc antenna). 2. In a transmission system having standing waves, a point at which the voltage is a minimum. voltage offset -The amount of dc voltage present at an (instnunentation) amplitier’s output with a 0-volt input. Initial offset may be adjusted to zero; however, offsetvoltage shifts during operation can cause errors. Systems containing microcomputers can often correct offset with an auto-zero cycle, or the offset can be removed by a control adjustment. voltage plane-A conductor or portion of a conductor layer on or in a printed board that is maintained at other than ground potential. It can also be used as a common voltage source for heat sinking or for shielding. woltage quadrupler - A rectifier circuit in which four diodes are employed to produce a dc voltage of four times the peak value of the ac input voltage. voltage-range multiplier -Also called an instrument multiplier. 1. A series resistor installed external to

DC

VOLTS OC

=

4 x PEAK VOLTS AC

Voltage quadqler. the measurement device to extend its voltage range. 2. A precision resistor placed in series with a voltmeter to enable measurement of a high voltage with a voltmeter having a lower voltage range. voltage rating-Also called the working voltage. 1. The maximum voltage that an electrical device or component can sustain without breaking down. 2. The maximum sustained voltage that can be safely applied to a capacitor up to a specified temperature without risking capacitor failure. 3. The maximum voltage at which a given device may be safely maintained during continuous use in a normal manner. voltage ratio (of a transformer) -Ratio of therms primary terminal voltage to the rms secondary terminal voltage under specified load conditions. voltage-ratio box-See measurement voltage divider. voltage reference- A highly regulated voltage source used as a standard to which the output voltage of a power supply is continuously compared for purposes of regulation. voltage-reference diode-A diode that develops across its terminals a reference voltage of specified accuracy when biased to operate within a specified current range. voltage-reference tube-A gas tube in which the voltage drop is essentially constant over the operating range of current and is relatively stable at fixed values of current and temperature. voltage reflection coefficient-The ratio of the complex electric field strength or voltage of a reflected wave to that of the incident wave. voltage-regulating transformer-A saturatedcore type of transformer that holds the output voltage to within a few percent, with input variations up to f 2 0 percent. Considerable harmonic distortion results unless extensive filters are employed. voltage regulation-A measure of the degree to which a power source maintains its output voltage stability under varying load conditions. voltage regulator- 1. A circuit that holds an output voltage at a predetermined value or causes it to vary according to a predetermined plan, regardless of normal input-voltage change or changes in the load impedance. 2. A gas-filled electronic tube that has the property of maintaining a nearly constant voltage across its terminals over a considerable range of current through the tube. It is used in an electronic voltage regulator. 3. An electronic circuit used for controlling and maintaining a voltage at a constant level. voltage-regulator diode-1. A diode that develops across its terminals an essentially constant voltage throughout a specified current range. 2. A diode that is

voltage-regulator tube

- voltmeter sensitivity

normally biased to operate in the breakdown region of its voltage-current characteristic and that develops across its terminals an essentially constant voltage throughout a specified current range. voltage-regulator tube- Also called a VR tube. A glow-discharge cold-cathode tube in which the voltage drop is essentially constant over the operating range of current, and which is designed to provide a regulated direct-voltage output.

R

T POWER DC FROM SUPPLY

@

OUTPUT

Voltage-regulator tube.

voltage relay-A relay that functions at a predetermined value of voltage. voltage saturation-See plate saturation. voltage-sensitive resistor-A resistor (e.g., a varistor) whose resistance varies with the applied voltage. voltage sensitivity- 1. The voltage that produces standard deflection of a galvanometer when impressed on a circuit made up of the galvanometer coil and the external critical-damping resistance. The voltage sensitivity is equal to the product of the current sensitivity and the total circuit resistance. 2. See voltage coefficient of capacitance. voltage spectrum-A function that is the square root of the spectral intensity; it is expressed in terms of voltage in a unit frequency band. gas-filled glowvoltage-stabilizing tube -A discharge tube normally working in that part of its characteristic where the voltage is practically independent of current drop within a given range. voltage standard -An accurately known voltage source (e.g., a standard cell) used for comparison with or calibration of other voltages. voltage standing-wave ratio-Abbreviated VSWR. In a stationary-wave system (such as in a waveguide or coaxial cable), the ratio of the amplitude of the electric field or voltage at a voltage maximum to that at an adjacent voltage minimum. voltage stress-That stress found within a material when subjected to an electrical charge. voltage-to-frequency converter -Abbreviated v/f converter. An electronic circuit that converts an input voltage into a train of digital output pulses at a rate that is directly proportional to the input. voltage to ground-The voltage between any live conductor of a circuit and earth (or common reference plane). voltage transformer-See potential transformer. voltage transients-Unpredictable and usually unavoidable spikes and surges of electrical power. voltage tripler -A rectifier circuit in which three diodes are employed to produce dc voltage equal to approximately three times the peak ac input voltage. voltage-tunable magnetron -A high-frequency continuous-wave oscillator operating in the microwave region. Power outputs begin in the milliwatts range and extend through hundreds of watts. voltage-tunable tube- An oscillator tube whose operating frequency can be changed by varying one or

838 more of its electrode voltages (e.g., a backward-wave magnetron). voltage-tuned cavity oscillator -Primarily a cavity oscillator with the addition of a varactor diode to slightly modify the cavity’s resonant frequency. These oscillators are capable of FM and/or phase-locking. voltage-tuned crystal oscillator-A crystalcontrolled oscillator with a varactor diode in the frequency-determining network that is used to slightly vary the crystal frequency. voltage-type telemeter-A telemeter in which the translating means is the magnitude of a single voltage. voltage-variable capacitance diode- Another name for varactor diode. voltage-variable capacitor-See varactor. voltage velocity limit -See slew rate, 2. voltaic cell -An electric cell having two electrodes of unlike metals immersed in a solution that chemically affects one or both of them, thus producing an electromotive force. The name is derived from Volta, a physicist who discovered this effect. voltaic couple-mo dissimilar metals in contact, resulting in a contact potential difference. voltaic pile -A voltage source consisting of alternate pairs of dissimilar metal discs separated by moistened pads, forming a number of elementary primary cells in series. volt-ammeter- An instrument calibrated to read both voltage and current. voltampere-Letter symbol: VA. A unit of apparent power in an ac circuit containing reactance. It is equal to the potential in volts multiplied by the current in amperes, without taking phase into consideration. voltamperehour meter- An electricity meter that measures the integral, usually in kilovoltamperehours, of the apparent power in the circuit where the meter is connected. voltampere loss- See apparent power loss. voltampere meter- An instrument for measuring the apparent power in an alternating-current circuit. Its scale is graduated in voltamperes or kilovoltamperes. voltampere reactive -Also called wattless power. Component of the apparent power in an altematingcurrent circuit that is delivered to the circuit during part of a cycle, but is returned to the source during another part of the cycle. The practical unit of reactive power is the var, equal to 1 reactive voltampere. Volta’s law-When two dissimilar conductors are placed in contact, the same contact potential is developed between them, whether the contact is direct or through one or more intermediate conductors. volt box-See measurement voltage divider. volt-electron -An obsolete expression for electronvolt. voltmeter-I. An instrument for measuring potential difference between two points. Its scale is usually graduated in volts. If graduated in millivolts or kilovolts, the instrument is usually designated as a millivoltmeter or a kilovoltmeter. 2. An instrument used for the measurement of electric voltage. The instrument may be of the electrostatic or tube type, but usually consists of a moving-coil ammeter connected in series with a high resistance. The resistance of the meter being fixed, the current passing through it will be directly proportional to the voltage at the points where it is connected; thus, the instrument can be calibrated in volts. voltmeter-ammeter-A voltmeter and an m e t e r combined into a single case, but with separate circuits. voltmeter sensitivity-The ratio, expressed in ohms per volt, of the total resistance of a voltmeter to its full-scale reading.

839 volt-ohm-milliammeter-A test instrument with several ranges, for measwhg voltage, current, and resistance. VOlUm&-Also called power level. I. The magnitude (measured on a standard volume indicator) of a complex audio-frequency wave, expressed in volume units. In addition, the term volume is used loosely to signify either the intensity of a sound or the magnitude of an audiofrequency wave. 2. The amount or a measure of energy in an electrical or acoustical train of waves. 3. -A physical unit of storage media; for example, a reel of magnetic tape. A volume may contain part of a file, a complete file, or more than one file. Sections of one or more files may be contained in a volume, but not multiple sections of the same file. 4. The level of an audio signal or the intensity of a sound. 5. A unit of secondary storage media, such as a magnetic tape, disk pack, or flexible diskette. volume bar-When activated, a TV feature that displays a volume setting bar on-screen, showing the adjustment being made whenever volume levels are adjusted. volunie compressioni--Also called automatic volume compression. The limiting of the volume range to about 30 to 40 decibels at the transmitter to permit a higher average percentage modulation without overmoddation. Also used in recording to raise the signal-to-noise ratio. volunie compressor -Audio-frequency control circuit that limits the volume range of a (radio) program at the transmitter to permit using a higher average percent modulation without risk of overmodulation. volume conductivity-See conductivity, I. volume control --A variable resistor for adjusting the loudness of a radio receiver or amplifying device. volume equivalent--A measure of the loudness of speech reproduced over a complete telephone connection. It is expressed numerically in terms of the trunk loss of a working reference system that has been adjusted to give equal loudness. volume expander- A circuit that provides volume expansion. vosolume e x p a n s i o n -See automatic volume expansion. volume indicator -An instrument for indicating the volume of a complex electric wave such as that corresponding to speech. v o l u m e lifetime -The average time interval between the generation and recombination of minority carriers in a homogeneous semiconductor. volume limiter-An amplifier whose gain is automatically reduced when lthe average input volume to the amplifier exceeds a predetermined value, so that the output volume is maintained substantially constant. The normal gain is restored whenever the input volume drops below the predetermined limit. volume-limiting amplifier- An amplifier that reduces the gain whenever the input volume exceeds a predetermined value, so that the output volume is maintained substantially constant. The normal gain is restored whenever the input volume drops below the predetermined limit. volume magnetostriction -The relative volume change of a body of ferromagnetic material when the magnetization of the hody is increased from zero to a specified value (usually saturation) under specified conditions. volume range-1. Of a transmission system, the difference, expressed in dB, between the maximum and minimum volumes that the system can satisfactorily handle. 2. Of a complex audio-fpequency signal, the

volt-ohm-milliammeter

-

difference, expressed in dB, between the maximum and minimum volumes occurring over a specified period. volume recombination rate-The rate at which free electrons and holes recombine within the volume of a semiconductor. v o l u m e resistance-Ratio of the dc voltage applied to two electrodes in contact with or embedded in a specimen to the portion of the current between them distributed through the specimen. volume resistivity- 1. Ratio of the potential gradient parallel to the current in a material to the current density. See also resistivity, 1. 2. Also called specific insulation resistance. The electrical resistance between opposite faces of a 1-cm cube of insulating material, commonly expressed in ohm-centimeters. 3. The resistance of a material to dc current as a measure of volume. Expressed in ohm-centimeters. volumetric displacement -The change in volume required to displace the diaphragm of a pressure transducer from its rest position to a position corresponding to the application of a stimulus equal to the rated range of the transducer. volumetric efficiency--Also called packing iactor. The ratio of parts volume to total equipment volume, expressed in percent. In modules, it is usually taken as the volume of component bodies only (not including leads, other interconnecting media, insnIators, heat sinks. and so on) and based on nominal sizes of components and nominal outside module dimensions. volumetric radar -A radar capable of producing three-dimensional position data on several targets. volumetric sensor-A sensor with a detection zone that extends over a volume such as an entire room, part of a room or a passageway. Ultrasonic motion detectors and sonic motion detectors are examples of voIumetric sensors. volume unit-Abbreviated vu. 1. The unit of transmission measurement for measuring the level of nonsteady-state currents. Zero level is the steady-state reference power of 1 milliwatt in a cirmit of 600 ohms characteristic impedance. 2. A measure of the power level of the voice wave. Zero volume unit is equivalent to +4 dBm for simple electrical waves (single frequencies). 3. An arbitrary sound-level standard related to the decibel and used for calibrating recording levels. volume-unit 'rndicator-Also called a vu indicator or volume-unit meter. An instrument calibrated to read audio-frequency power levels directly in volume wits. volume-unit meter -See vu meter. volume velocity-The rate ab which a medium flows through a specified area due to a sound wave. Von Hippel b r e a k d o w n theory- Also called lowenergy criterion. Breakdown occurs at fields for which the rate of recombination of electrons and positive holes is less than the rate of collisional ionization. Assumes no distribution in electron energies. VOR -Abbreviation for VHF omnirange. vortex amplifier- 1. A fluidic device in which the angular rate of a vortex is controlled to alter the output. 2. A fluidic amplifier using momentum interaction to produce stream rotation and consequent output modification. vowel articulation-The percent of articulation obtained when the speech units considered are vowels, usually combined with consonants into meaningless syllables. VR -See virtual reality. V-ring -In commutator construction. a specially shaped insulating structure having one or more V-shaped sections. VRR- Abbreviation for visual radio range. VR tube -Abbreviation for voltage-regulator tube.

VSWR

- vu meter

VSWR -Abbreviation for voltage standing-wave ratio. VTF -Abbreviation for vertical tracking force. VTL -Abbreviation for variable threshold logic. VTM -See voltage-tunable magnetron. VTR -Abbreviation for videotape recording or videotape recorder. VTVM -Abbreviation for vacuum-tube voltmeter. VU -Abbreviation for volume unit. vu indicator- Abbreviation for volume-unit indicator. vulcanized fiber- A dense, homogeneous, cellulosic material that has been partially gelantinized by swelling with a zinc chloride solution. It may be made in the form of sheets, rods, coils, or tubes, and it may be used for electrical insulation as well as in mechanical applications. VU meter- Abbreviation for volume-unit meter. 1. A volume indicator with a decibel scale and specified dynamic and other characteristics. It is used to obtain correlated readings of speech power necessitated by the rapid fluctuations in a level of voice currents. 2. Strictly, a recording-level meter whose indicator needle’s motion is damped according to a specified standard to allow it to respond at a certain speed to sudden impulses without

-

840

overshooting the mark by more than a certain amount. The term vu meter is loosely applied to practically any recording-level indicator that uses an indicator needle, 3. A type of recording-level indicator that shows average signal levels in decibels relative to a fixed O-dB reference level or in percent of maximum recommended modulation. The term is frequently used for any level meter using this scale, but it applies mostly to meters having a specified, standard degree of damping.

PROGRAM

600n VU METER

II

r-

--,-- -

75M)i-I-

vu meter.

7

n I1

W

W- 1. Letter symbol for watt. 2. Symbol for energy or work. wafer-1. A thin semiconductor slice of silicon or germanium with parallel faces on which matrices of microcircuits or individual semiconductors can be formed. After processing, the wafer is separated into dice or chips containing individual circuits. 2. A single section of a wafer switch. 3. Slice of semiconductor crystal material used as substrate for monolithic ICs, diodes, and transistors. 4. The thin slice of semiconductor crystal from which many hundreds or tlhousands of single monolithic device chips are ultimately obtained. Normally all techniques, such as epitaxy, photolithography, diffusion, and passivation, are carried out on the wafer before it is scribed and broken into individual dice. 5. A thin slice, typically 5 to 30 mils thick, sawed from a cylindrical ingot (boule) of bulk semiconductor material (silicon or gallium arsenide), 4 to 8 or more inches in diameter. Arrays of ICs or discrete devices are fabricated in the wafers during the manufacturing process. Thi: wafer is then tested, scribed, and broken apart to produce semiconductor chips. wafer and die sorters-Equipment that automates the testing and sorting of semiconductor devices from wafer form. wafer fabrication-me process of epitaxial growth, impurity diffusion, oxide deposition, and metallization that forms the semiconductor devices on the wafer. wafer-handling equipment--Equipment used for processing silicon wafers using methods that include batch processing in a common carrier, air-bearing singlewafer processing, and a combination of batch and singlewafer processing. wafer probing-An electrical test of devices on the wafer, utilizing tiny probes to make contact with the metallized pads on the die. wafer socket -A vacuum-tube socket that consists of two punched sheets or wafers of an insulating material, separated by spring-metal (clipsthat grip the terminal pins of the inserted tube. wafer switch-A rotary multiposition switch with fixed terminals on ceramic or Bakelite wafers. The rotor arm, in the center, is positioned by a shaft. Several decks may be stacked onto one switch and rotated by a common shaft.

Wagner ground-A bridge with an additional pair of ratio arms, onto which the ground connection to the bridge is moved in order to effect a perfect balance, free from error. WAIS-See wide area information service. wait-A computer system service that causes a task to be suspended for a specified time or pending the occurrence of an event. waiting time- 1. In certain tubes (e.g., thyratrons), the time that must elapse between the turning on of their heaters and the application of plate voltage. 2. See access time, 1. Waldo -Mechanical hands that function as an extension of human hands, such as those used to handle radioactive materials. Now a scientific reality, the idea was first used in Robert A. Heinkin’s classic story “Waldo,” from whence came the name. walkie-lookie -A compact, portable television camera used for remote broadcasts. The resultant electrical pulses are transmitted by microwave radio to a local control point for retransmission over a standard television station. walkie-talkie -1. A two-way radio communication set designed to be carried by one person, usually strapped to the back, and capable of being operated while in motion. 2. A hand-held transceiver.

-0

SECTION A-A

Walkie-talkie, 2.

Wafer switch.

841

w a l k test light

- watthour-demand meter

walk test light-A light on motion detectors that comes on when the detector senses motion in the area. It is used while setting the sensitivity of the detector and during routine checking and maintenance. walkthrough --Programming by giving a robot instructions one by one, with the robot executing each before receiving the next. The speed of the robot is increased when programming i s satisfactory. A teach box is usually used. wall-attachment amplifier- 1. A family of fluidic elements that make use of flow-created low-pressure regions, causing fluid to adhere to an amplifier wall in a controlled manner. 2. A fluidic device in which the control of the attachment of a stream to a wall@) (Coanda effect) alters the output. wall box-A metal box placed in the wall and containing switches, fuses, etc. wall outlet-A spring-contact device to which a portable lamp or appliance is connected by means of a plug attached to a flexible cord. The wall outlet is installed in a box and connected permanently to the power-line wiring of a home or building. walls-The sides of the groove in a disc record. Walmsley antenna -An array of vertical rectangular loops with a height of one wavelength and a spacing of one-half wavelength. The loops are arranged in parallel planes and are series fed at the centers of the longer, vertical sides, with appropriate transpositions of the feed lines. Walsh radiator-A type of speaker driver invented by Lincoln Walsh, in which a gently sloping cone, moving up and down, so displaces the air with its sloped sides as to radiate a cylindrical wavefront in a 360" horizontal circle. wamoscope -Abbreviation for a wave-modulated oscilloscope. A cathode-ray tube that includes detection, amplification, and display of a microwave signal in a single envelope, thus eliminating the local oscillator, mixer, IF amplifier, detector, video amplifier, and associated circuitry in a conventional radar receiver. Tubes are available for a range of 2 to 4 GHz. WAN-Abbreviation for wide area network. A network that serves an area of hundreds or thousands of miles, using common-carrier-provided lines. Contrast with LAN. wander -See scintillation, 2. warble-tone generator -An oscillator whose frequency is varied cyclically at a subaudio rate over a fixed range. It is usually used with an integrating detector to obtain an averaged transmission or crosstalk measurement. warm boot-Also called soft start or warm start. 1. Partial restarting of a computer under operating system control without turning it off and on again. 2. Resetting the computer while power is on. See also soft start. warm-up time-1. In an indirectly heated tube, the time that elapses, after the heater is turned on, before the cathode reaches its optimum operating temperature. 2. The time, following power application to a device, required for the output to stabilize within specifications. warning net -Communications system established for the purpose of disseminating warning information of enemy movement or action to all interested commands. w a s h o u t emitter process-A process used in the manufacture of semiconductor devices. It involves use of the same mask for both the emitter diffusion and the deposition of the ohmic contact. The aluminum metallization for the contact is permitted to form in the same hole that was used for the diffusion. waste instruction -See no-operation instruction. watch -See radio watch.

842

watchdog -In control systems, a combination of hardware and software that acts as an interlock scheme, disconnecting the system's output from the process in event of system malfunction. water-activated battery-A primary battery that contains the electrolyte but requires the addition of (or immersion in) water before it becomes usable. water-cooled tube-A vacuum tube having an anode structure projecting through the glass envelope and constructed to permit circulation of water around the anode for cooling purposes during operation. water load-A matched waveguide termination in which the electromagnetic energy is absorbed in water. The output power is calculated from the difference in temperature between the water at the input and output. waterproof motor-A totally enclosed motor so constructed that it will exclude water applied in the form of a stream from a hose. Leakage may occur around the shaft, provided it is prevented from entering the oil reservoir and provision is made for automatically draining the motor. The means for automatic draining may be a check valve, or a tapped hole at the lowest part of the frame that will serve for application of a drain pipe. WATS -Abbreviation for Wide Area Telephone Service. Also called 800 or 888 service. 1. A service provided by telephone companies in the United States that permits a customer to make calls to or from telephones in a specific nonlocal zone for a flat monthly charge. 2. A service that, among other things, allows people almost anywhere in the United States to call-without charge to them-a certain number. A familiar arrangement has a business paying monthly fees for a so-called 800 number that can be dialed by the public. In-WATS allows a central customer to call out. watt-Letter symbol: W. 1. A unit of the electric power required to do work at the rate of 1 joule per second. It is the power expended when 1 ampere of direct current flows through a resistance of 1 ohm. In an alternating-current circuit, the true power in watts is effective voltamperes multiplied by the circuit power factor. (There are 746 watts in 1 horsepower.) 2. A measure of electrical or acoustical power. The electrical wattage rating of an amplifier describes the power it can develop to drive a loudspeaker. Acoustical wattage describes the actual sound produced by a loudspeaker in the given environment. (The two figures, in any given amplifier-speaker system, are necessarily very widely divergent inasmuch as the low efficiency of speakers necessitates their receiving relatively large amounts of amplifier power in order to produce satisfactory sound levels.) wattage rating-1. The maximum power that a device can safely handle. 2. The maximum power that the resistor can dissipate, assuming a specific life, a standard ambient temperature, and a stated long-term drift from its no-load value. Increasing the ambient temperature or reducing the allowable deviation from the initial value (more-stable resistance value) requires derating the allowable dissipation. With few exceptions, resistors are derated linearly from full wattage at rated temperature to zero wattage at the maximum temperature. watthour-A unit of electrical work indicating the expenditure of 1 watt of electrical power for 1 hour. Equal to 3600 joules. w a t t h o u r capacity-The number of watthours delivered by a storage battery at a specified temperature, rate of discharge, and final voltage. watthour constant of a meter-The registration, expressed in watthours, corresponding to one revolution of the rotor. watthour-demand meter-A combined watthour meter and demand meter.

watthour meter - waveform generator

843 watthour meter-1. An electricity meter that measures and registers the integral, usually in kilowatthours, of the active power of the circuit into which the meter is connected. This power integral is the energy delivered to the circuit during the iintegration interval. 2. A totalizing meter that registers the total electrical energy used, usually in kilowatthours. wattless componeflt- A reactive component. wattless power-Se,e reactive power. watt !oss--See power loss, 2. wattmeter -An instrument for measuring the magnitude of the active power in an electric circuit. Its scale is usually graduated in watts. If graduated in kilowatts or megawatts, the instrument is usually designated as a kilowattmeter or megawattmeter. attsecond-The amount of energy corresponding to 1 watt acting for 1 second. It is equal to 1 joule. wattseco~dconstant of a meter-The registration, in wattseconds, corresponding to one revolution of the rotor. wave -I. A physical activity that rises and falls, or advances and retreats, periodically as it travels through a medium. 2. Propagated disturbance, usually periodic, such as a radio wave or sound wave. If the periodic motion is regular and recurring, it is said to be aperiodic or damped. wave amplitude -The maximum change from zero of the characteristic of a wave. wave analyzer -An electric instrument for measuring the amplitude and frequency of the various components of a complex current or voltage wave. wave angle-The angle at which a wave is propagated from one point to another. wave antenna- Also called a Beverage antenna. A directional antenna composed of a parallel horizontal conductor one-half to several wavelengths long, and terminated to ground in its characteristic impedance at the far and. wawe band- 1. A band of frequencies, such as that assigned to a particular type of communication service. nd of frequencies comprising an electrical wave. band switch --A multiposition switch for the frequency band tuned by a receiver or r. clutter-CClutte:r caused on a radar screen by echoes from sea waves. wave converter-A. device for changing a wave from on12pattern to another (e.g., baffle-plate, grating, and sheath-reshaping converters for waveguides). wave duct- 1. A tubular waveguide capable of concentrating the propagation of waves within it. 2. A natural duct formed in air by atmospheric conditions. Waves of certain frequencies travel through it with more than average efficiency. wave equation-An equation that gives a mathematical specification of a wave process or describes the performance of a medlium through which a wave is passing. wave filter-A transducer for separating waves on the basis of their frequency. It introduces a relatively small insertion loss to waves in one or more frequency bands, and a relatively large insertion loss to waves of other frequencies. See aZso filter, 1. wave fluxing-A wave solder fluxing method. Flux is applied using the liquid wave principle to form a double-sided parabolic wave. Washing action of the wave promotes flux coverage of the underside surfaces, while capillary forces promote t h - h o l e penetration. See also brush fluxing; foam fluxing; spray fluxing. waveform-1. The shape of an electromagnetic wave. 2. A graphical representation of the relationship

between voltage, current, or power against time. It also provides a picture of the behavior of signals at given frequencies. 3. A geometrical shape as obtained by displaying a characteristic voltage or current as a function of time. 4. The variations in magnitude and polarity of a current or voltage with respect to time, plotted in graphic form. I

I

DC WAVEFORM

1

I

SAWTOOTH WAVEFORM

RANDOM VARYING WAVEFORM

PERIODIC ALTESNATING WAVEFORM

Waveforms,2.

wavef orm-amplitude distortion-Sometimes called amplitnde distortion. Nonlinear waveform distortion caused by unequal attenuation or amplification between the input and output of a device. waveform analyzer- 1. An instrument that measures the amplitude and frequency of the components in a complex waveform. 2. A frequency-selective voltmeter that can be used to determine the frequency and amplitude of each sine-wave component of a complex wave. 3. An instrument that measures the amplitude of a waveform over a specific period, with resolution usually in the low nanosecond range. waveform digitization-The earliest approach taken for speech synthesis. The technique relies on sampling of the waveform in the time domain at twice the highest frequency of interest (this is known as the Nyquist rate). Critical to the use of this technique is data compression; otherwise, memory requirements are prohibitive. waveform encoding -A synthesis technique that reproduces speech by reconstructing the original speech waveform. waveform error- A change in measurement accuracy of an average-reading ac meter, occurring when the waveform of the measured voltage or current departs from a pure sine-wave form. waveform generator-Also called arbitrary waveform generator. 1. See timing-pulse distributor. 2. An instrumentation that does not necessarily employ mathematically derived relationships between the output voltage and the time base to produce its output waveshape. Most generators of this type develop an output that follows a waveshape drawn out or copied manually from some existing natural phenomenon (e.g., an EKG trace or the stress versus elongation curve from a pull-to-fracture test of a metal sample) or specified via keyboard entries. The waveform may also follow tracings made manually on an accompanying digitizer tablet.

waveform influence

- wavelength

waveform influence-The change in meter indication of the applied current and/or voltage caused solely by a change in waveform from a specified waveform. waveform monitor -1. An oscilloscope designed for viewing signal waveforms. 2. An oscilloscope designed especially for viewing the waveform of a video signal. waveform recorder -A general-purpose, waveform-capturing instrument with high-speed, high-resolution analog-to-digital converters and digital memory. waveform synthesizer -Equipment for generating a signal of a desired waveform. wavefront-1. With respect to a wave in space, a continuous surface at every point of which the displacement from zero in the positive or negative direction is the same at any instant. In a periodic wave, the displacements of the points on a wavefront are in phase. For a surface wave, the wavefront is a continuous line whose points have the same properties as do the points in the wavefront of a wave in space. 2. That part of a signal-wave envelope between the initial point of the envelope and the point at which the envelope reaches its crest. 3. For a field of electromagnetic energy emanating from a source, the wavefront is a surface connecting all field points that are equidistant from the source. 4. A surface at right angles to rays that proceed from the wave source. The surface passes through those parts of the wave that are in the same phase and travel in the same direction. For parallel rays, the wavefront is a plane; for rays that radiate from a point, the wavefront is spherical. wave function-In a wave equation, a point function that specifies the amplitude of a wave. waveguide- 1. A system of material designed to confine direct electromagnetic waves in a direction determined by its physical boundaries. 2. A transmission line comprising a hollow conducting tube (rectangular or tubular) within which electromagnetic waves are propagated on a solid dielectric or dielectric-filled conductor. waveguide attenuator -A waveguide device for producing attenuation by some means (e.g., by absorption and reflection). waveguide connector-Also called a waveguide coupling. A mechanical device for electrically joining parts of a waveguide system together. waveguide coupling -See waveguide connector. waveguide critical dimension -The dimension of waveguide cross section that determines the cutoff frequency. waveguide cutoff frequency- Also called the critical frequency. The frequency limit of propagation, along a waveguide, for waves of a given field configuration. waveguide dummy load-Sections of waveguide for dissipating all the power entering the input flange. waveguide elbow-A bend in a waveguide.

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