The Illustrated Dictionary of Electronics Illustrated...The Illustrated Dictionary of Electronics Eighth Edition Stan Gibilisco Editor-in-Chief McGraw-Hill New York Chicago San Francisco

TheIllustrated Dictionary of

Electronics

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TheIllustrated Dictionary

of ElectronicsEighth Edition

Stan GibiliscoEditor-in-Chief

McGraw-HillNew York Chicago San Francisco Lisbon London Madrid

Mexico City Milan New Delhi San Juan SeoulSingapore Sydney Toronto

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Cataloging-in-Publication Data is on file with the Library of Congress

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To Tony, Tim, and Samuelfrom Uncle Stan

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Contents

Preface ixAcknowledgments xi

Dictionary 1Appendix A Schematic Symbols 773Appendix B Tables and Data 787

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Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

Preface

The Illustrated Dictionary of Electronics—8th Edition has been revised, clarified, and up-dated, reflecting technological advances of recent years. New definitions have been added inthe fields of wireless technology, robotics, and artificial intelligence. Every effort has beenmade to be concise and accurate, without “talking down” to the reader.

Many definitions contain cross references (indicated in ALL CAPITALS); these providerecommended additional information or allow comparison with related terms. Expressions ofspecial significance are printed in italics. Electronics abbreviations are included in the text;the full terms are stated as definitions.

While an effort has been made to avoid superfluous mathematics, equations are some-times necessary to completely and effectively define a term. Mathematics beyond the high-school level has not been used.

Appendix A contains the standard symbols used in electrical and electronic diagrams.These symbols are used in illustrations throughout this dictionary. Appendix B contains thefollowing data tables:

1. Conversion between electrical systems2. Greek alphabet3. Mathematical functions and operations4. Prefix multipliers5. Resistor color code

Suggestions for future editions are welcome.Stan Gibilisco

Editor-in-Chief

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Acknowledgments

Illustrations in this book were generated with CorelDRAW. Some clip art is courtesy of CorelCorporation, 1600 Carling Avenue, Ottawa, Ontario, Canada K1Z 8R7.

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TheIllustrated Dictionary of

Electronics

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Abbe condenser 1. In microscopy, a special two-piece lens that has enhanced light-gatheringpower. 2. A similar focusing device in an electro-magnetic antenna.

abbreviated dialing In telephone systems, specialcircuits requiring fewer-than-normal dialing op-erations to connect subscribers.

abc 1. Abbreviation of AUTOMATIC BASS COM-PENSATION, a system for boosting the volume ofbass sounds at low amplifier gain. 2. Abbrevi-ation of AUTOMATIC BIAS CONTROL. 3. Abbrevi-ation of AUTOMATIC BRIGHTNESS CONTROL.4. Abbreviation of AUTOMATIC BRIGHTNESSCOMPENSATION.

abcoulomb The unit of electrical quantity in thecgs electromagnetic system. One abcoulombequals 10 coulombs and is the quantity of elec-tricity that flows past any point in a circuit in onesecond when the current is one abampere.

aberration 1. Distortion from perfect shape in alens or reflecting mirror or antenna dish. 2. Asmall error in the determination of the directionof a source of electromagnetic energy, on accountof the motion of the source and/or the detectingapparatus. 3. A small displacement in the appar-ent positions of the stars from month to month onaccount of the earth’s orbital motion.

ABETS Acronym for airborne beacon electronic testset (NASA).

abfarad The unit of capacitance in the cgs electro-magnetic system. One abfarad equals 109 faradsand is the capacitance across which a charge of1 abcoulomb produces a potential of 1 abvolt.

abhenry The unit of inductance in the cgs electro-magnetic system. One abhenry equals 10–9 henry

A 1. Symbol for GAIN. 2. Symbol for AREA. 3. Sym-bol for AMPERE (SI unit for current).

A� Symbol for negative terminal of filament-voltagesource in a vacuum-tube circuit.

A� Symbol for positive terminal of filament-voltagesource in a vacuum-tube circuit.

a 1. Abbreviation of ATTO- (prefix). 2. Abbreviationof AREA. 3. Abbreviation of ACCELERATION. 4. Abbreviation of ANODE. 5. Obsolete abbrevia-tion of cgs prefix AB-.

aA 1. Abbreviation of attoampere. 2. Obsolete forABAMPERE.

AAAS Abbreviation for American Association for theAdvancement of Science.

AAC Abbreviation of automatic aperture control(NASA).

AAS Abbreviation of advanced antenna system(NASA).

AASR Abbreviation of airport and airways surveil-lance radar.

AB Abbreviation of acquisition beacon (NASA).A-B In sound and acoustics, the direct comparison

of two sources of sound by alternately turning onone and the other.

ab- 1. Prefix that transforms the name of a practi-cal electrical unit to that of the equivalent electro-magnetic cgs unit (e.g., ABAMPERE, ABOHM,ABVOLT). See individual entries of such cgsunits. 2. Abbreviation for ABSOLUTE.

abac A graphic device for the solution of electronicsproblems. Also see ALIGNMENT CHART.

abampere The unit of current in the cgs electro-magnetic system. One abampere equals 10amperes and corresponds to 1 abcoulomb persecond.

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and is the inductance across which a currentthat changes at the rate of 1 abampere per sec-ond induces a potential of 1 abvolt.

ABL Abbreviation of Automated Biology Laboratory(NASA).

abmho The obsolete unit of conductance and ofconductivity in the cgs electromagnetic system.Replaced with ABSIEMENS.

abnormal dissipation Power dissipation higher orlower than the customary level, usually an over-load.

abnormal oscillation 1. Oscillation where none isdesired or expected, as in an amplifier. 2. Oscilla-tion at two or more frequencies simultaneouslywhen single-frequency operation is expected.3. Oscillation at an incorrect frequency. 4. Parasiticoscillation.

abnormal propagation 1. The chance shifting ofthe normal path of a radio wave, as by displace-ments in the ionosphere, so that reception is de-graded. 2. Unintentional radiation of energy fromsome point other than the transmitting antenna.3. Propagation over a path or in a direction notexpected.

abnormal reflections Sharp, intense reflections atfrequencies higher than the critical frequency ofthe ionosphere’s ionized layer.

abnormal termination The shutdown of a runningcomputer program or other process. Caused bythe detection of an error by the associated hard-ware that indicates that some ongoing series ofactions cannot be executed correctly.

abnormal triggering The false triggering or switch-ing of a circuit or device, such as a flip-flop, bysome undesirable source instead of the true triggersignal. Electrical noise pulses often cause abnor-mal triggering.

abohm The unit of resistance and of resistivity inthe cgs electromagnetic system. One abohmequals 10–9 ohms and is the resistance acrosswhich a steady current of 1 abampere produces apotential difference of 1 abvolt.

abort To deliberately terminate an operation, ex-periment, process, or project before it has run itsnormal course.

AB power pack 1. A portable dry-cell or wet-cellarray containing both A and B batteries in onepackage. 2. An ac-operated unit in one packagefor supplying A and B voltages to equipment nor-mally operated from batteries.

abrasion machine An instrument for determiningthe abrasive resistance of a wire or cable.

abrasion resistance A measure of the ability of awire or wire covering to resist mechanical dam-age.

ABS A basic programming abbreviation for the ab-solute value (of a number, variable, or expres-sion).

abscissa 1. The independent variable in a function.2. The axis (usually horizontal) on the graph of afunction that indicates the independent variable.

absence-of-ground searching selector A rotaryswitch that searches for an ungrounded contactin a dial telephone system.

absiemens The unit of conductance or conductiv-ity in the cgs electromagnetic system. Oneabsiemens equals 109 siemens and is theconductance through which a potential of 1 ab-volt forces a current of 1 abampere.

absolute 1. A temperature scale in which zero repre-sents the complete absence of heat. Units of mea-sure are same as units on Celsius and Fahrenheitscales. See ABSOLUTE SCALE. 2. Independent ofany arbitrarily assigned units of measure or value.

absolute accuracy The full-scale accuracy of a me-ter with respect to a primary (absolute) standard.

absolute address In a digital computer program,the location of a word in memory, as opposed tolocation of the word in the program.

absolute code A computer code in which the exactaddress is given for storing or locating the refer-ence operand.

absolute coding In computer practice, coding thatuses absolute addresses.

absolute constant A mathematical constant thathas the same value wherever it is used.

absolute delay The time elapsing between thetransmission of two synchronized signals fromthe same station or from different stations, as inradio, radar, or loran. By extension, the time in-terval between two such signals from any source,as from a generator.

absolute digital position transducer A digital po-sition transducer whose output signal indicatesabsolute position. (See ENCODER.)

absolute efficiency The ratio Xx/Xs, where Xx isthe output of a given device, and Xs is the outputof an ideal device of the same kind under thesame operating conditions.

absolute encoder system A system that permitsthe encoding of any function (linear, nonlinear,continuous, step, and so on) and supplies a non-ambiguous output.

absolute error The difference indicated by the ap-proximate value of a quantity minus the actual

2 abhenry • absolute error

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absolute Peltier coefficient The product of theabsolute Seebeck coefficient and absolute tem-perature of a material.

absolute pitch A tone in a standard scale, deter-mined according to the rate of vibration, indepen-dent of other tones in the range of pitch.

absolute pressure Pressure (force per unit area) ofa gas or liquid determined with respect to that ofa vacuum (taken as zero).

absolute-pressure transducer A transducer actu-ated by pressure from the outputs of two differentpressure sources, and whose own output is pro-portional to the difference between the two ap-plied pressures.

absolute scale 1. A scale in which the zero valueindicates the lowest physically possible value thata parameter can attain. 2. A standard scale for measurement of a quantity. 3. A universallyagreed-upon scale for the determination of a vari-able quantity. 4. The Kelvin temperature scale. 5. The Rankine temperature scale.

absolute Seebeck coefficient The quotient, as anintegral from absolute zero to the given tempera-ture, of the Thomson coefficient of a material di-vided by its absolute temperature.

absolute spectral response The frequency outputor response of a device in absolute power units(such as milliwatts) as opposed to relative units(such as decibels).

absolute system of units A system of units inwhich the fundamental (ABSOLUTE) units arethose expressing length (l), mass (m), charge (q),and time (t). All other physical units, includingpractical ones, are then derived from these abso-lute units.

absolute temperature Temperature measured oneither the Kelvin or Rankine scales, where zerorepresents the total absence of heat energy.

absolute temperature scale 1. The Kelvin temper-ature scale, in which the divisions are equal insize to 1° Celsius, and the zero point is absolutezero, the coldest possible temperature, approxi-mately –273.16° Celsius. 2. The Rankine temper-ature scale, in which the divisions are equal insize to 1° Fahrenheit, and the zero point is abso-lute zero or approximately –459.7° Fahrenheit.

absolute tolerance The value of a component as itdeviates from the specified or nominal value. It isusually expressed as a percentage of the specifiedvalue.

value. This difference is positive when the ap-proximate value is higher than the exact value,and it is negative when the approximate value islower than the exact value. Compare RELATIVEERROR.

absolute gain Antenna gain for a given orientationwhen the reference antenna is isolated in spaceand has no main axis of propagation.

absolute humidity The mass of water vapor perunit volume of air. Compare RELATIVE HUMID-ITY.

absolute instruction A computer instruction thatstates explicitly and causes the execution of aspecific operation.

absolute magnitude For a complex number quan-tity, the vector sum of the real and imaginarycomponents (i.e., the square root of the sum ofthe squares of those components). Also see AB-SOLUTE VALUE and IMPEDANCE.

absolute maximum rating The highest value aquantity can have before malfunction or damageoccurs.

absolute maximum supply voltage The highestsupply voltage that can be applied to a circuitwithout permanently altering its characteristics.

absolute measurement of current Measurementof a current directly in terms of defining quan-tities. 1. TANGENT GALVANOMETER method:Current is proportional to the tangent of the an-gle of deflection of the needle of this instrument.Deflection depends on torque, resulting from themagnetic field produced by current in the gal-vanometer coil acting against the horizontalcomponent of the earth’s magnetic field. 2. ELECTRODYNAMOMETER method: With this2-coil instrument, current is determined fromthe observed deflection, the torque of the sus-pension fiber of the movable coil, and the coil di-mensions.

absolute measurement of voltage Measurementof a voltage directly in terms of defining quan-tities. 1. CALORIMETRIC method: A current-carrying coil immersed in water raises thetemperature of the water. The difference ofpotential that forces the current through the coilthen is determined in terms of the equivalent heatenergy. 2. Disk-electrometer method: In thissetup, a metal disk attached to one end of abalance beam is attracted by a stationary diskmounted below it, the voltage being applied to thetwo disks. The other end of the beam carries apan into which accurate weights are placed. Atbalance, the voltage is determined in terms of theweight required to restore balance, the upper-diskarea, and the disk separation.

absolute minimum resistance The resistance be-tween the wiper and the nearer terminal of a po-tentiometer, when the wiper is as close to thatterminal as physically possible. All potentiome-ters have two such specifications, one for eachend terminal.

absolute error • absolute tolerance 3

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absolute units Fundamental physical units (seeABSOLUTE SYSTEM OF UNITS) from which allothers are derived. See, for example, AMPERE,OHM, VOLT, and WATT.

absolute value The magnitude of a quantity with-out regard to sign or direction. The absolute valueof a is written |a|. The absolute value of a posi-tive number is the number itself; thus, |10|equals 10. The absolute value of a negative num-ber is the number with its sign changed: |-10|equals 10.

absolute-value circuit A circuit that produces aunipolar signal in response to a bipolar input andin proportion to the absolute value of the magni-tude of the input.

absolute-value computer A computer in whichdata is processed in its absolute form; i.e., everyvariable maintains its full value. (Compare toINCREMENTAL COMPUTER.)

absolute-value device In computer practice, a de-vice that delivers a constant-polarity outputsignal equal in amplitude to that of the inputsignal. Thus, the output signal always has thesame sign.

absolute zero The temperature –273.16°C(�459.7°F and 0 Kelvin). The coldest possibletemperature, representing the complete absenceof heat energy.

absorbed wave A radio wave that dissipates in theionosphere as a result of molecular agitation.This effect is most pronounced at low andmedium frequencies.

absorptance The amount of radiant energy ab-sorbed in a material; equal to 1 minus the trans-mittance.

absorption The taking up of one material or me-dium by another into itself, as by sucking orsoaking up. Also, the retention of one medium (ora part of it) by another medium, through whichthe first one attempts to pass. See, for example,ABSORBED WAVE, ABSORPTION COEFFI-CIENT, DIELECTRIC ABSORPTION. CompareADSORPTION.

absorption band See ABSORPTION SPECTRUM.absorption circuit A circuit that absorbs energy

from another circuit or from a signal source—es-pecially a resonant circuit, such as a wavemeteror wavetrap.

absorption current In a capacitor, the current re-sulting from absorption of energy by the dielectricmaterial.

absorption dynamometer A power-measuring in-strument in which a brake absorbs energy from arevolving shaft or wheel.

absorption fading Fading of a radio wave, result-ing from (usually) slow changes in the absorptionof the wave in the line of propagation.

absorption frequency meter See WAVEMETER.absorption line See ABSORPTION SPECTRUM.absorption loss 1. Transmission loss caused by

dissipation of electrical energy, or conversion of it

into heat or other forms of energy. 2. Loss of all orpart of a skywave because of absorption by theionosphere. Also called ionospheric absorption oratmospheric absorption.

absorption marker A small blip introduced ontoan oscilloscope trace to indicate a frequencypoint. It is so called because it is produced by theaction of a frequency-calibrated tuned trap, simi-lar to an absorption wavemeter.

absorption modulation Amplitude modulation of atransmitter or oscillator by means of an audio-frequency-actuated absorber circuit. In its simplestform, the modulator consists of a few turns of wirecoupled to the transmitter tank coil and con-nected to a carbon microphone. The arrangementabsorbs energy from the transmitter at a varyingrate as the microphone changes its resistance inaccordance with the sound waves it receives.

4 absolute units • A-B test

absorption spectrum For electromagnetic waves, aplot of absorption coefficient (of the medium ofpropagation) versus frequency. Also called EMIS-SION SPECTRUM.

absorption trap See WAVETRAP.absorption wavemeter A resonant-frequency indi-

cating instrument that is inductively coupled tothe device under test.

absorptivity In audio and microwave technologies,a measure of the energy absorbed by a given vol-ume of material.

A-B test Comparison of two sounds by reproduc-ing them in alternating succession.

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acceleration at stall The angular acceleration of aservomotor at stall, determined from the stalltorque and the moment of inertia of the motor’srotor.

acceleration derivative Acceleration (a) expressedas the second derivative of distance (s) with re-spect to time (t): a equals d2s/dt2.

acceleration potential See ACCELERATINGVOLTAGE.

acceleration switch A switch that operates auto-matically when the acceleration of a body towhich it is attached exceeds a predetermined ratein a given direction.

acceleration time The time required by a com-puter to take in or deliver information after inter-preting instructions. Compare ACCESS TIME.

acceleration torque During the accelerating pe-riod of a motor, the difference between the torquedemanded and the torque actually produced bythe motor.

acceleration voltage The potential between accel-erating elements in a vacuum tube, the value ofwhich determines average electron velocity.

accelerometer A transducer whose output voltageis proportional to the acceleration of the movingbody to which it is attached.

accentuation The emphasis of a desired band offrequencies, usually in the audio-frequency spec-trum.

abvolt The unit of potential difference in the cgselectromagnetic system. One abvolt equals 10–8 Vand is the difference of potential between any twopoints when 1 erg of work is required to move 1abcoulomb of electricity between them.

abwatt The unit of power in the cgs electromagneticsystem. One abwatt equals 10�7 W and is thepower corresponding to 1 erg of work per second.

ac 1. Abbreviation of ALTERNATING CURRENT.2. Abbreviation of ATTITUDE CONTROL. 3. Ab-breviation of AERODYNAMIC CENTER. 4. A suf-fix meaning AUTOMATIC CALCULATOR orAUTOMATIC COMPUTER.

a/c 1. Abbreviation of AIRCRAFT. 2. Abbreviationof AIR CONDITIONING.

Ac Symbol for ACTINIUM.ACA Abbreviation of automatic circuit analyzer.ac base current Symbol, IB(ac). The ac component of

base current in a bipolar transistor.ac base resistance Symbol, RB (ac). The dynamic

base resistance in a bipolar transistor.ac base voltage Symbol, VB(ac). The ac component

of base voltage in a bipolar transistor. It is the acinput signal voltage in a common-emitter ampli-fier or emitter-follower amplifier.

ac bias In a tape recorder, the high-frequency cur-rent that passes through the recording head tolinearize operation.

acc 1. Abbreviation of AUTOMATIC CHROMI-NANCE CONTROL. 2. Abbreviation of AUTO-MATIC COLOR COMPENSATION. 3. Abbreviationof ACCELERATION.

ac cathode current Symbol, IK(ac). The ac compo-nent of cathode current in an electron tube.

ac cathode resistance Symbol, RK(ac). The dynamiccathode resistance in an electron tube. RK(ac)equals dVK/dIK for a constant value of VG.

ac cathode voltage Symbol, VK(ac). The ac compo-nent of cathode voltage in an electron tube. It isthe ac output signal voltage in cathode-followerand grounded-grid amplifiers.

accelerated life test A test program that simu-lates the effects of time on devices or apparatus,by artificially speeding up the aging process.

accelerated service test A service or bench test inwhich equipment or a circuit is subjected to anextreme condition in an attempt to simulate theeffects of average use over a long time.

accelerating conductor or relay A conductor orrelay that prompts the operation of a succeedingdevice in a starting mode according to establishedconditions.

accelerating electrode In a cathode-ray tube orklystron, the electrode to which the acceleratingvoltage is applied.

accelerating time The elapsed time that startswhen voltage is applied to a motor, and endswhen the motor shaft reaches maximum speed.

accelerating voltage A positive high voltage appliedto the accelerating electrode of a cathode-ray tubeto increase the velocity of electrons in the beam.

abvolt • accentuation 5

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accentuator A circuit or device, such as a filter,tone control, or equalizer, used to emphasize aband of frequencies, usually in the audio-frequency spectrum. Also see ACCENTUATION.

acceptable-environmental-range test A test todisclose the environmental conditions that equip-ment can endure while maintaining at least theminimum desired reliability.

acceptable quality level Abbreviation, AQL. A per-centage that represents an acceptable average ofdefective components allowable for a process, orthe lowest quality that a supplier is permitted toregularly present for acceptance.

acceptance sampling plan A probabilistic methodof sampling a quantity of units from a lot, and de-termining from the sample whether to accept thelot, reject the lot, or perform another sampling.

acceptance test A test performed on incomingequipment or on submitted samples to determineif they meet tester’s or supplier’s specifications.

acceptor 1. Any device or circuit, such as a series-resonant circuit, that provides relatively easytransmission of a signal, in effect accepting thesignal. 2. A hole-rich impurity added to a semi-conductor to make the latter p-type. It is so calledbecause its holes can accept electrons. CompareDONOR.

acceptor circuit See ACCEPTOR, 1.acceptor impurity See ACCEPTOR, 2.access 1. To gain entrance to something, such as

the interior of the cabinet of a high-fidelity ampli-fier. 2. In a computer, the action of going to a spe-cific memory location for the purpose of dataretrieval. 3. A port or opening into a piece ofequipment, placed there to make the equipmenteasy to maintain and repair.

access arm A mechanical device that positions theread/write mechanism in a computer storage unit.

access control register A register that is part of acomputer protection system that prevents inter-ference between different software modules.

access method A method of transferring informa-tion or data from main storage to an input/out-put unit.

access right The access status given to computersystem users that indicates the method of accesspermitted (e.g., read a file only or write to a file).

access time The time required by a computer tobegin delivering information after the memory orstorage has been interrogated.

accidental error An unintentional error commit-ted by a person making measurements andrecording data.

accidental triggering The undesired chance-operation of a flip-flop or other switching circuitcaused by a noise pulse or other extraneous sig-nal.

ac collector current Symbol, IC(ac). The ac compo-nent of collector current in a bipolar transistor.

ac collector resistance Symbol, RC(ac). The dy-namic collector resistance of a bipolar transistor.

RC(ac) equals dVC/dIC for a constant value of basecurrent IB (in a common-emitter circuit) or emit-ter current IE (in a common-base circuit).

ac collector voltage Symbol, VC(ac). The ac compo-nent of collector voltage in a bipolar transistor.The ac output signal voltage in a common-emitteror common-base amplifier.

accompanying audio channel The RF signal thatsupplies television sound. Also called Cochannnelsound frequency.

ac component In a complex wave (i.e., one con-taining both ac and dc), the alternating, fluctu-ating, or pulsating part of the combination.Compare DC COMPONENT.

accordion A printed-circuit connector contact witha Z-shaped spring that allows high deflectionwith low fatigue.

ac-coupled flip-flop A flip-flop that is operated bythe rise or fall of a clock pulse.

ac coupling Transformer coupling or capacitivecoupling, which transmit ac, but not dc. CompareDIRECT COUPLING.

6 accentuator • accuracy rating

accumulator 1. In a digital computer, a circuit orregister device that receives numbers, totalsthem, and stores them. 2. Storage battery.

accuracy 1. Precision in the measurement ofquantities and in the statement of physical char-acteristics. 2. Degree of precision. Usually ex-pressed, in terms of error, as a percentage of thespecified value (e.g., 10 V plus or minus 1%), as apercentage of a range (e.g., 2% of full scale), or asparts (e.g., 100 parts per million).

accuracy rating The maximum error in an instru-ment, given as a percentage of the full-scalevalue.

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ac generator 1. A rotating electromagnetic ma-chine that produces alternating current (e.g., adynamo or alternator). 2. An oscillator or com-bination of an oscillator and an output ampli-fier.

ac grid voltage Symbol, VG(ac). The ac componentof control grid voltage in an electron tube. The acinput signal voltage in a common-cathode ampli-fier or cathode follower.

A channel The left channel of a two-channel stereosystem.

achieved reliability A statement of reliability basedon the performance of mass-produced parts orsystems under similar environmental conditions.Also called OPERATIONAL RELIABILITY.

achromatic 1. Without color. In a TV image, thetones from black through gray to white. The termoccasionally refers to black-and-white television,although MONOCHROMATIC is more often usedin this sense.

achromatic locus Also called achromatic region.An area on a chromaticity diagram that containsall points, representing acceptable referencewhite standards.

achromatic scale A musical scale without acci-dentals.

ACIA Abbreviation of asynchronous communica-tions interface adapter.

acicular Pertaining to the shape of magnetic parti-cles on recording tape. Under magnification,these particles look like thin rods.

acid A substance that dissociates in water solutionand forms hydrogen (H) ions (e.g., sulfuric acid).Compare BASE, 2.

acid depolarizer Also called acidic depolarizer.An acid, in addition to the electrolyte, used insome primary cells to slow the process of polar-ization.

ac line A power line that delivers alternating cur-rent only.

ac line filter A filter designed to remove extrane-ous signals or electrical noise from an ac powerline, while causing virtually no reduction of thepower-line voltage or power.

ac line voltage The voltage commonly deliveredby the commercial power line to consumers. Inthe United States, the two standards are 117 Vand 234 V (~ about 5 percent). The lower voltageis used by most appliances; the higher voltage isintended for appliances and equipment thatdraws high power, such as electric ovens, cook-ing ranges, clothes dryers, and amateur-radioamplifiers. In Europe, 220 V is the commonstandard.

aclinic line Also called magnetic equator. An imag-inary line drawn on a map of the world or of anarea that connects points of zero inclination (dip)of the needle of a magnetic compass.

ACM Abbreviation for Association for ComputingMachinery.

ac magnetic bias See AC BIAS.

accw Abbreviation of ALTERNATING-CURRENTCONTINUOUS WAVE.

ac/dc Abbreviation of ALTERNATING CURRENT/DIRECT CURRENT. Pertains to equipment thatwill operate from either ac utility power or a dcpower source. A notebook computer is a good ex-ample.

ac directional overcurrent relay A relay thatworks on a specific value of alternating overcur-rent that is rectified for a desired polarity.

ac drain current Symbol, ID(ac). The ac componentof drain current in a field-effect transistor.

ac drain resistance Symbol, RD(ac). The dynamicdrain resistance in a field-effect transistor; RD(ac)equals dVD/dID for a constant value of gate volt-age VG.

ac drain voltage Symbol, VD(ac). The ac componentof drain voltage in a field-effect transistor. The acoutput signal voltage in a common-source FETamplifier.

ac dump The removal of all ac power from a systemor component.

ac emitter current Symbol, IE(ac). The ac compo-nent of emitter current in a bipolar transistor.

ac emitter resistance Symbol, RE(ac). The dynamicemitter resistance of a bipolar transistor; RE(ac)equals dVE/dIE for a constant value of base cur-rent IB (in an emitter-follower circuit) or collectorvoltage VCC (in a common-base circuit).

ac emitter voltage Symbol, VE(ac). The ac compo-nent of emitter voltage in a bipolar transistor. Theac input signal voltage in a common-base ampli-fier; the ac output signal voltage in an emitter-follower amplifier.

ac equipment An apparatus designed for opera-tion from an ac power source only. Compare DCEQUIPMENT and AC/DC.

ac erasing In tape recording, the technique of us-ing an alternating magnetic field to erase materialalready recorded on the tape.

ac erasing head Also called ac erase head. In tapeand wire recording, a head that carries alternat-ing current to erase material already recorded onthe tape or wire. Also see AC ERASING.

acetate Cellulose acetate, a tough thermoplasticmaterial that is an acetic acid ester of cellulose. Itis used as a dielectric and in the manufacture ofphotographic films.

acetate base 1. The cellulose acetate film thatserved as the base for the magnetic oxide coatingin early recording tape. Most such tapes todayare of polyester base. 2. The cellulose acetatesubstrate onto which certain photosensitive ma-terials are deposited for lithographic reproduc-tion. Also see ACETATE and ANCHORAGE.

acetate tape Recording tape consisting of a mag-netic oxide coating on a cellulose acetate film.Also see ACETATE BASE.

ac gate voltage Symbol, VG(ac). The ac componentof gate voltage in a field-effect transistor. The acinput signal voltage.

accw • ac magnetic bias 7

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ac meter A meter that is intended to work only onalternating current or voltage. Such meters in-clude iron-vane and rectifier types.

quencies. If one fork is struck and then broughtnear the other, the second fork will begin vibrating.If the second fork has a fundamental frequencythat is a harmonic of the frequency of the first fork,the second fork will vibrate at its own resonantfrequency. See HARMONIC, RESONANCE.

acoustic coupling Data transfer via a sound linkbetween a telephone and a pickup/reproducer.Was once common in computer terminals andfacsimile machines. This scheme has been largelyreplaced by hard wiring and optical coupling.

acoustic damping The deadening or reduction ofthe vibration of a body to eliminate (or cause todie out quickly) sound waves arising from it.

acoustic delay line Any equivalent of a specialtransmission line that introduces a useful timedelay between input and output signals. In oneform, it consists of a crystal block or bar with aninput transducer at one end and an output trans-ducer at the other. An electrical input signal inthe first transducer sets up sound waves thattravel through the interior of the crystal; thepiezoelectric reaction of the crystal to sound vi-brations sets up an output voltage in the secondtransducer. The delay is caused by the time re-quired for the acoustic energy to travel the lengthof the crystal bar.

8 ac meter • acoustic feedback

ac noise 1. Electromagnetic interference originat-ing in the ac power lines. 2. Electrical noise of arapidly alternating or pulsating nature.

ac noise immunity In computer practice, the abil-ity of a logic circuit to maintain its state, despiteexcitation by ac noise.

acous Abbreviation for ACOUSTIC.acoustic Pertaining to audible sound distur-

bances, usually in air (versus audio-frequencycurrents or voltages).

acoustic absorption The assimilation of energyfrom sound waves passing through or reflected bya given medium.

acoustic absorption loss That portion of soundenergy lost (as by dissipation in the form of heat)because of ACOUSTIC ABSORPTION.

acoustic absorptivity The ratio of sound energyabsorbed by a material to sound energy strikingthe surface of the material.

acoustic attenuation constant The real-numbercomponent of the complex acoustical propagationconstant, expressed in nepers per unit distance.

acoustic burglar alarm An alarm that receives thenoise made by an intruder. The alarm device re-sponds to the impulses from concealed micro-phones.

acoustic capacitance The acoustic equivalent ofelectrical capacitance.

acoustic clarifier In a loudspeaker system, a set ofcones attached to the baffle that vibrate to absorband suppress sound energy during loud bursts.

acoustic communication Communications bymeans of sound waves. This can be through theatmosphere, or it can be through solids or liq-uids, such as a taut wire, a body of water, or theearth.

acoustic compliance COMPLIANCE in acoustictransducers, especially loudspeakers. It is equiv-alent to electrical capacitive reactance.

acoustic consonance An effect that occurs whentwo objects are near each other but not in physicalcontact, and both have identical or harmonicallyrelated resonant frequencies. An example is shownby two tuning forks with identical fundamental fre-

acoustic depth finder A direct-reading device fordetermining the depth of a body of water, or forlocating underwater objects via sonic or ultra-sonic waves transmitted downward and reflectedback to the instrument.

acoustic dispersion Variation of the velocity ofsound waves, depending on their frequency.

acoustic elasticity 1. In a loudspeaker enclosure,the compressibility of air behind the vibratingcone of the speaker. 2. In general, the compress-ibility of any medium through which soundpasses.

acoustic electric transducer A transducer, suchas a microphone or hydrophone, that convertssound energy into electrical energy. CompareELECTRICAL/ACOUSTIC TRANSDUCER. Alsosee ACOUSTIC TRANSDUCER.

acoustic feedback A usually undesirable effectthat occurs when sound waves from a loud-speaker (or other reproducer) reach a microphone(or other input transducer) in the same system.

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acoustic line Baffles or other such structureswithin a speaker that act as the mechanical equiv-alent of an electrical transmission line to enhancethe reproduction of very low bass frequencies.

acoustic load A device that serves simultaneouslyas the output load of an amplifier and as a trans-ducer of electrical energy into acoustic energy(e.g., headphones or a loudspeaker).

acoustic memory In a computer, a volatile mem-ory element employing an acoustic delay line, of-ten incorporating quartz or mercury as thetransmission and delay element.

acoustic mirage A type of sound distortion inwhich the listener experiences the illusion of twosound sources when there is only one. The phe-nomenon is caused by the effect of a large tem-perature gradient in the air or water throughwhich the sound passes.

acoustic mode Crystal-lattice vibration withoutproducing an oscillating dipole.

acoustic noise Interferential (usually disagreeable)sounds carried by the air (or other propagationmedium) to the ear or to an acoustic transducer.This is in contrast to electrical noise, which con-sists of extraneous current or voltage impulsesand is inaudible until converted into sound.

acoustic ohm The unit of acoustic resistance, re-actance, or impedance. One acoustic ohm equalsthe volume velocity of 1 cm/s produced by asound pressure of 1 microbar (0.1 Pa). Also calledacoustical ohm.

acoustic phase constant The imaginary-numbercomponent of the complex acoustic propagationconstant expressed in radians per second or radi-ans per unit distance.

acoustic phase inverter A bass reflex loudspeakerenclosure.

acoustic pressure 1. The acoustic equivalent ofelectromotive force, expressed in dynes persquare centimeter; also called acoustical pres-sure. 2. Sound pressure level.

acoustic propagation The transmission of soundwaves, or subaudible or ultrasonic waves, as adisturbance in a medium, rather than as an elec-tric current or electromagnetic field.

acoustic radiator A device that emits soundwaves. Examples are the cone of a loudspeaker,the diaphragm of a headphone, and the vibratingreed of a buzzer.

This can cause an amplifier to oscillate, with a re-sultant rumbling, howling, or whistling.

acoustic filter Any sound-absorbing or transmit-ting arrangement, or combination of the two, thattransmits sound waves of desired frequency whileattenuating or eliminating others.

acoustic frequency response The sound-frequency range as a function of sound intensity.A means of describing the performance of anacoustic device.

acoustic generator A device that produces soundwaves of a desired frequency and/or intensity.Examples are electrical devices (headphones orloudspeakers operated from a suitable oscillator,buzzer, bell, or flame) and mechanical devices(tuning forks, bells, string, or whistles).

acoustic grating A set of bars or slits that are par-allel to one another and arranged a fixed distanceapart so that an interference pattern forms assound passes through. Used to determine thewavelength of acoustic waves.

acoustic homing system 1. A system that uses asound signal for guidance purposes. 2. A guid-ance method in which a missile homes in onnoise generated by a target.

acoustic horn A tapered tube (round or rectangu-lar, but generally funnel-shaped) that directssound and, to some extent, amplifies it. So calledto distinguish it from a microwave horn.

acoustic howl See ACOUSTIC FEEDBACK.acoustician 1. A person skilled in acoustics (an

acoustics technician). 2. An AUDIOLOGIST.acoustic impedance Unit, ACOUSTIC OHM. The

acoustic equivalent of electrical impedance. Likethe latter, acoustic impedance is the total opposi-tion encountered by acoustic force. Also like elec-trical impedance, acoustic impedance hasresistive and reactive components: ACOUSTICRESISTANCE and ACOUSTIC REACTANCE.

acoustic inductance Also called inertance. Theacoustic equivalent of electrical inductance.

acoustic inertance See ACOUSTIC INDUCTANCE.acoustic inhibition See AUDITORY INHIBITION.acoustic intensity See SOUND INTENSITY.acoustic interferometer An instrument that eval-

uates the frequency and velocity of sound wavesin a liquid or gas, in terms of a standing wave setup by a transducer and reflector as the frequencyor transducer-to-reflector distance varies.

acoustic labyrinth A loudspeaker enclosurewhose internal partitions form a maze-like pathor “tube” lined with sound-absorbing material.The tube effectively runs from the back of thespeaker down to where it terminates in a MOUTHor PORT that opens at the front of the enclosure.The labyrinth provides an extremely efficient re-production system because of its excellent acous-tic impedance-matching capability.

acoustic lens A system of barriers that refractssound waves the way that an optical lens doeswith light waves.

acoustic feedback • acoustic radiator 9

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acoustic radiometer An instrument for measuringthe intensity of a sound wave (see SOUND IN-TENSITY) in terms of the unidirectional steady-state pressure exerted at a boundary as a resultof absorption or reflection of the wave.

acoustic reactance Unit, ACOUSTIC OHM. Theimaginary-number component of ACOUSTICIMPEDANCE. It can take the form of ACOUSTICCAPACITANCE or ACOUSTIC INDUCTANCE.

acoustic reflectivity The ratio Fr/Fi, where Fr isthe rate of flow of sound energy reflected from asurface and Fi is the rate of flow of sound energyincident to the surface.

acoustic refraction The deflection of sound wavesbeing transferred obliquely between media thattransmit sound at different speeds.

acoustic regeneration See ACOUSTIC FEEDBACK.acoustic resistance Unit, ACOUSTIC OHM. The

real-number component of ACOUSTIC IMPE-DANCE. The opposing force that causes acousticenergy to be dissipated in the form of heat. It isattributed to molecular friction in the mediumthrough which sound passes. See ACOUSTICOHM.

acoustic resonance In an enclosed chamber withwalls that reflect sound waves, resonance that oc-curs at certain wavelengths because the echoescombine in and out of phase. Speaker enclosuresalmost always have resonance at certain frequen-cies. This effect can be used to an advantage whenit is necessary to get good bass (low-frequency)response from a relatively small speaker.

acoustic resonator 1. A chamber, such as a box,cylinder, or pipe, in which an air column resonatesat a particular frequency. 2. A piezoelectric, mag-netostrictive, or electrostrictive body that vibratesat a resonant audio frequency that is governed bythe mechanical dimensions of the body when anaudio voltage at that frequency is applied.

acoustic scattering The spreading of a soundwave in many directions as a result of diffraction,reflection, or refraction.

acoustic suspension A loudspeaker design thatallows exceptional low-frequency reproductionfor a fairly small physical size. An airtight enclo-sure is used to increase the tension on thespeaker cone.

acoustic system 1. A coordinated array of acous-tic components (e.g., acoustic filters, resonators,etc.) that responds to sound energy in a predeter-mined manner. 2. An audio-frequency system inwhich sound energy is converted into electricalenergy, processed, and then reconverted intosound energy for a clearly defined purpose.

acoustic telegraph A telegraph that gives audiblesignals, as opposed to visual signals or printedmessages.

acoustic transducer 1. Any device, such as head-phones or a loudspeaker, for converting audio-frequency electrical signals into sound waves. 2.Any device, such as a microphone, for convertingsound waves into alternating, pulsating, or fluc-tuating currents.

acoustic transmission The direct transmission ofsound energy without the intermediary of electriccurrents.

acoustic transmission system A set of compo-nents designed to generate acoustic waves.

acoustic transmissivity Also called acoustictransmitivity. The ratio et/ei, where et is thesound energy transmitted by a medium, and ei isthe incident sound energy reaching the surface ofthe medium. Acoustic transmissivity is propor-tional to the angle of incidence.

acoustic treatment Application of sound-absorb-ing materials to the interior of an enclosure orroom to control reverberation.

acoustic wave The traveling vibration, consistingof molecular motion, via which sound is trans-mitted through a gas, liquid or solid. Usuallyrefers to sound waves in air.

acoustic wave filter See ACOUSTIC FILTER.acoustoelectric effect The generation of a voltage

across the faces of a crystal by sound waves trav-eling longitudinally through the crystal.

acoustoelectronics A branch of electronics con-cerned with the interaction of sound energy andelectrical energy in devices, such as surface-wavefilters and amplifiers. In such devices, electricallyinduced acoustic waves travel along the surfaceof a piezoelectric chip and generate electrical en-ergy. Also called praetersonics and microwaveacoustics.

ac plate current Symbol, IP(ac). The ac componentof plate current in a vacuum tube.

ac plate resistance Symbol, RP(ac). The dynamicplate resistance of an electron tube. RP(ac) equalsdEP/dIP, where EP is the plate voltage and IP is theplate current, for a constant value for grid volt-age EG.

10 acoustic radiometer • ac plate resistance

acoustics 1. The physics of sound. The study andapplications of acoustic phenomena. 2. The qual-ities of an enclosure or sound chamber (room,auditorium, or box) that describe how soundwaves behave in it.

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ac source voltage Symbol, VS(ac). The ac compo-nent of source voltage in a field-effect transistor.The ac output-signal voltage in a source-follower(grounded-drain) FET amplifier.

acss Abbreviation of analog computer subsystem.ac time overcurrent relay A device with a certain

time characteristic, which breaks a circuit whenthe current exceeds a certain level.

actinic rays Short-wavelength light rays in the vi-olet and ultraviolet portion of the spectrum thatgive conspicuous photochemical action.

actinism The property whereby radiant energy(such as visible and ultraviolet light, X-rays, etc.)causes chemical reactions.

actinium Symbol, Ac. A radioactive metallic ele-ment. Atomic number, 89. Atomic weight, 227.

actinodielectric Exhibiting a temporary rise inelectrical conductivity during exposure to light.

actinoelectric effect The property whereby cer-tain materials (such as selenium, cadmium sul-fide, germanium, and silicon) change theirelectrical resistance or generate a voltage on ex-posure to light. Also see ACTINODIELECTRIC.

actinometer An instrument for measuring the di-rect heating power of the sun’s rays or the actinicpower of a light source.

action current A small transient current thatflows in a nerve in the human body as a result ofstimulation.

activate To start an operation, usually by applyingan appropriate enabling signal.

activation 1. Supplying electrolyte to a battery cellto prepare the cell for operation. 2. Causing theacceleration of a chemical reaction.

activation time In the activation of a battery cell(see ACTIVATION, 1), the interval between addi-tion of the electrolyte and attainment of full cellvoltage.

activator A substance added to an accelerator (seeACCELERATOR, 3) to speed the action of the ac-celerator.

active Pertaining to a circuit or device that re-quires a power supply for its operation. This dif-fers from a passive circuit or device, whichoperates with no external source of power.

active antenna An antenna that uses a smallwhip, loop, or ferrite loopstick with a high-gainamplifier for receiving at very-low, low, medium,and high radio frequencies (approximately 9 kHzto 30 MHz).

active area The forward-current-carrying portionof the rectifying junction of a metallic rectifier.

active arm See ACTIVE LEG.active balance In telephone repeater operation, the

sum of return currents at a terminal network bal-anced against the local circuit or drop resistance.

active chord mechanism Abbreviation, ACM. Inrobots, an electromechanical gripper capable ofconforming to irregular objects. It has a structuresimilar to the human spine, with numeroussmall, rigid links connected by hinges.

ac plate voltage Symbol, EP(ac). The ac componentof plate voltage in an electron tube. The ac out-put-signal voltage in a common-cathode ampli-fier.

ac power Symbol, Pac. Unit, watt (W). The poweracting in an ac circuit, Pac equals EI cos q, whereE is in volts, I in amperes, and q is the phase an-gle. Compare DC POWER. Also see POWER.

ac power supply A power unit that supplies aconly (e.g., ac generator, vibrator-transformer, os-cillator, or inverter). Compare DC POWERSUPPLY.

acquisition 1. The gathering of data from trans-ducers or a computer. 2. Locating the path of anorbiting body for purposes of collecting teleme-tered data. 3. Orienting an antenna for optimumpickup of telemetered data.

acquisition and tracking radar An airborne orground radar, which locks in on a strong signaland tracks the body that reflects (or transmits)the signal.

acquisition radar A radar that spots an oncomingtarget and supplies position data regarding thetarget to a fire-control or missile-guidance radar,which then tracks the target.

acr 1. Abbreviation of AUDIO CASSETTE RE-CORDER. 2. Abbreviation of AUDIO CASSETTERECORDING SYSTEM.

ac reclosing relay The controlling component inan alternating-current circuit breaker. It causesthe breaker to reset after a specified period oftime.

ac relay A relay designed to operate on alternatingcurrent without chattering or vibrating.

ac resistance Pure resistance in an ac circuit. Un-like reactance and impedance, which are alsoforms of opposition to the flow of current, ac re-sistance introduces no phase shift.

acronym A word formed from letters or syllablestaken from other applicable words of a multiwordterm. Acronyms are convenient for naming newdevices and processes in electronics. Usually, aterm is considered an acronym only when it isspelled in all-capital letters; once the term is ac-cepted and popularized, it is written as a conven-tional word and is no longer thought of as anacronym. For example, LASER was once anacronym for light amplification by the stimulatedemission of radiation. By the popularization pro-cess, the acronym became a conventional wordfrom which other terms (such as the verb “lase”)were derived.

acrylic resin A synthetic resin used as a dielectricand in electronic encapsulations. It is made fromacrylic acid or one of its derivatives.

ACS Abbreviation of automatic control system.ac source current Symbol, IS(ac). The ac component

of source current in a field-effect transistor.ac source resistance Symbol, RS(ac). The dynamic

source resistance in a field-effect transistor; RS(ac)equals dVS/dIS for a constant value of VG.

ac plate voltage • active chord mechanism 11

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active communications satellite A satellite con-taining receivers (which pick up beamed electro-magnetic signals from a ground point and amplifythem) and transmitters (which send signals backto the surface of the earth). Also called activecomsat. Compare PASSIVE COMMUNICATIONSSATELLITE.

active component 1. A device capable of some dy-namic function (such as amplification, oscilla-tion, or signal control) that usually requires apower supply for its operation. Examples includebipolar transistors, field-effect transistors, andintegrated circuits. Compare PASSIVE COMPO-NENT. 2. In an ac circuit, a quantity that con-tains no reactance so that the current is in phasewith the voltage.

active component of current See ACTIVE CUR-RENT.

active computer A computer in an installation ornetwork that is processing data.

active comsat See ACTIVE COMMUNICATIONSSATELLITE.

active control system A device or circuit thatcompensates for irregularities in the operatingenvironment.

active current In an ac circuit, the current compo-nent that is in phase with the voltage. This is incontrast to reactive current, which is not in phasewith the voltage, and is “inactive,” with respect topower in the circuit. The active current is equal tothe average power divided by the effective voltage.

active decoder An automatic ground-station de-vice that gives the number or letter designation ofa received radio beacon reply code.

active device 1. An electronic component, such as atransistor that needs a power supply, and/or thatis capable of amplifying. 2. Broadly, any device (in-cluding electromechanical relays) that can switch(or amplify) by application of low-level signals.

active electric network A network containing oneor more active devices or components, usuallyamplifiers or generators, in addition to passivedevices or components.

active element The driven or RF-excited elementin a multielement antenna or antenna array.

active file A computer file in use (i.e., one that isbeing updated or referred to).

active filter A bandpass, bandstop, highpass orlowpass filter, consisting of resistors, capacitors,and operational amplifiers, arranged to pass a de-sired frequency response. Commonly used at au-dio frequencies.

active infrared detection Detection of infraredrays reflected from a target to which they werebeamed.

active jamming Transmission or retransmissionof signals for the purpose of disrupting communi-cations.

active junction A pn junction in a semiconductordevice that has been created by a diffusion pro-cess.

active leg An element within a transducer thatchanges one or more of its electrical characteris-tics in response to the input signal of the trans-ducer. Also called active arm.

active lines In a U.S. television picture, the lines(approximately 488) that make up the picture.The remaining 37 of the 525 available lines areblanked and are called INACTIVE LINES.

active material 1. In a storage cell, the chemicalmaterial in the plates that provides the electricalaction of the cell, as distinguished from the sup-porting material of the plates themselves. 2. A ra-dioactive substance. 3. The phosphor coating of acathode-ray tube screen. 4. The material used tocoat an electron-tube cathode.

active mixer A signal mixer using one or more ac-tive components, such as transistors or in-tegrated circuits. An active circuit providesamplification, input-output isolation, and highinput impedance, in addition to the mixing ac-tion. Compare PASSIVE MIXER.

active modulator A modulator using one or moreactive components, such as transistors or inte-grated circuits. An active circuit provides gain,input-output isolation, and high input impe-dance, in addition to modulation. Compare PAS-SIVE MODULATOR.

active network See ACTIVE ELECTRIC NET-WORK.

active pressure The electromotive pressure thatproduces a current in an ac circuit.

active pull-up An arrangement using a transistoras a pull-up resistor replacement in an integratedcircuit, providing low output impedance and lowpower consumption.

active RC network 1. A resistance-capacitance(RC) circuit that contains active components(transistors or integrated circuits), as well as pas-sive components (capacitors and resistors). 2. AnRC network in which some or all of the resistorsand capacitors are simulated by the action of ac-tive components.

active repair time The time during which mainte-nance is done on a system and the system is outof operation.

12 active communications satellite • active repair time

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ily in the same physical location as the trueground surface (i.e., the earth itself ). An actualground can be an artificial ground plane, such asthat provided in some antenna structures. Actualground can also be modified by nearby rooftops,buildings, guy wiring, and utility wiring.

actual height The highest altitude where radiowave refraction actually occurs.

actual power Also called active or AVERAGEPOWER. Symbol, Pavg. In a resistive circuit undersine-wave conditions, average power is the prod-uct of the rms voltage and the rms current. It isalso equal to half the product of the maximumcurrent and maximum voltage.

actuating device A device or component that oper-ates electrical contacts to affect signal transmis-sion.

actuating system 1. An automatic or manuallyoperated system that starts, modifies, or stops anoperation. 2. A system that supplies energy forACTUATION.

actuating time Also called actuation time. Thetime interval between generation of a control sig-nal, or the mechanical operation of a control de-vice, and the resulting ACTUATION.

actuation 1. The starting, modification, or termi-nation of an operation or process. 2. Activation ofa mechanical or electromechanical switching de-vice.

actuator An electromechanical device that useselectromagnetism to produce a longitudinal or ro-tary thrust for mechanical work. It is often theend (load) device of a servosystem.

ACU Abbreviation of automatic calling unit.ac voltage A voltage, the average value of which is

zero, that periodically changes its polarity. In onecycle, an ac voltage starts at zero, rises to a max-imum positive value, returns to zero, rises to amaximum negative value, and finally returns tozero. The number of such cycles per second istermed the ac frequency.

ac voltmeter See AC METER.acyclic machine Also called ACYCLIC GENERA-

TOR. A dc generator in which voltage induced inthe active wires of the armature is always of thesame polarity.

A/D Abbreviation for ANALOG-TO-DIGITAL. SeeANALOG-TO-DIGITAL CONVERSION.

Ada A microcomputer language designed primarilyfor use in multi-computer systems, where eachsmall computer communicates with the others,providing some of the advantages of a larger com-puter.

Adam A communications code word sometimesused for phonetic verbalizing of the letter A. Morecommonly, ALPHA is used.

adapter 1. A fitting used to change either the ter-minal scheme or the size of a jack, plug, or socketto that of another. 2. A fitting used to provide atransition from one type or style of conductor toanother (e.g., waveguide to coaxial line). 3. An

active satellite • adapter 13

active satellite See ACTIVE COMMUNICATIONSSATELLITE.

active sensor In an electronic security system, atransducer that generates an electromagneticfield or acoustic-wave field, and detects changesin the field resulting from the presence or move-ment of objects in the vicinity.

active substrate In an integrated circuit, a sub-strate consisting of single-crystal semiconductormaterial into which the components are formed;it acts as some or all of the components. This is incontrast to a substrate consisting of a dielectric,where the components are deposited on the sur-face.

active system A radio and/or radar system thatrequires transmitting equipment to be carried ina vehicle.

active tracking system A system in which atransponder or responder on board a vehicle re-transmits information to tracking equipment(e.g., azusa, secor).

active transducer 1. A transducer that containsan active device, such as a transistor or inte-grated circuit, for immediate amplification of thesensed quantity. 2. A transducer that is itself anactive device.

active wire In the armature of a generator, a wireexperiencing induction and, therefore, is deliver-ing voltage.

activity 1. Intensity of, as well as readiness for, os-cillation in a piezoelectric crystal. 2. Radioactiveintensity. 3. Intensity of thermal agitation. 4.Thermionic emission of electrons.

activity ratio The ratio of active to inactive recordsin a computer file.

ac transducer A transducer that either requires anac supply voltage or delivers an ac output sig-nal—even when operated from a dc supply.

ac transmission The use of an alternating voltageto transfer power from one point to another, usu-ally from generators to a distribution center, andgenerally over a considerable distance.

actual ground The ground as “seen” by an an-tenna. The actual ground surface is not necessar-

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addend In a calculation, any number to be addedto another. Compare AUGEND.

addend register In a digital computer, the registerthat stores the addend.

adder 1. In a digital computer, the device or circuitthat performs binary addition. A HALF ADDER isa two-input circuit that can produce a sum out-put and a carry output, but it cannot accommo-date a carry signal from another adder. A FULLADDER can accommodate a carry input, as wellas two binary signals to be added. Also see ANA-LOG ADDER. 2. A circuit in a color TV receiverthat amplifies the receiver primary matrix signal.

additive 1. The character or characters added to acode to encipher it. 2. In a calculation, an itemthat is to be added. 3. An ingredient, usually in asmall quantity, added to another material to im-prove the latter in quality or performance.

additive color A color formed by combining therays from two or three primary-colored lightsonto a single neutral surface. For example, byprojecting a red and a green beam onto a neutralscreen, a yellow additive color results.

additive primaries Primary colors that form othercolors in a mixing of light (see ADDITIVE COLOR),but are not themselves formed by mixing otheradditive primaries. For example, red, green, andblue are the additive primaries used in color tele-vision. Through appropriate mixing, these colorscan be used to generate an unlimited variety ofother colors. Compare SUBTRACTIVE PRI-MARIES, which form the color spectrum by mix-ing pigments rather than lights. In additivesystems, each superimposed primary color in-creases the total light output from the reflecting(viewing) surface; in subtractive systems, each su-perimposed primary decreases the total reflectiv-ity. Thus, equal combination of additive primariesproduces gray or white, and equal combination ofsubtractive primaries produces gray or black.

addition record An extra data store created in acomputer during processing.

address 1. In computer operations, a usually nu-merical expression designating the location ofmaterial within the memory or the destination ofsuch material. 2. The accurately stated locationof information within a computer; a data pointwithin a grid, matrix, or table; a station within anetwork. 3. In computer operations, to select thelocation of stored information.

address comparator A device that ensures thatthe address being read is correct.

address computation In digital computer opera-tions, the technique of producing or modifyingonly the address part of an instruction.

address field In a computer, the part of the in-struction that gives the address of a bit of data (ora word) in the memory.

address generation The programmed generationof numbers or symbols used to retrieve recordsfrom a randomly stored direct-access file.

14 adapter • address generation

auxiliary system or unit used to extend the oper-ation of another system (e.g., a citizens-bandadapter for a broadcast receiver).

adaptive communication A method of communi-cation that adjusts itself according to the particu-lar requirements of a given time.

adaptive suspension vehicle Abbreviation, ASV.A specialized robot that moves on mechanicallegs, rather than on wheels. It generally has sixlegs and resembles an insect. It is designed tomove over extremely irregular or rocky terrain,and to carry a human passenger.

adaptivity The ability of a system to respond to itsenvironment by changing its performance char-acteristics.

adc Abbreviation of ANALOG-TO-DIGITAL CON-VERTER.

Adcock antenna A directional antenna systemconsisting of two vertical antennas, spaced insuch a way that the whole array behaves like aloop antenna. Its members are connected and po-sitioned so that it discriminates against horizon-tally polarized waves, and delivers output that isproportional to the vector difference of signal volt-ages induced in the two vertical arms.

Adcock direction finder A radio direction-findingsystem based on the directivity of the ADCOCKANTENNA.

Adcock radio range A radio range system withfour ADCOCK ANTENNAS situated at the cornersof a square, and a fifth antenna at the center ofthe square.

add-and-subtract relay A stepping relay that canbe switched either uprange (add) or downrange(subtract).

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from the picture signal in the next higher chan-nel and the sound signal in the next lowerchannel.

adjacent-channel selectivity The extent to whicha receiver or tuned circuit can receive on onechannel and reject signals from the nearest outly-ing channels.

adjacent sound channel In television, the radio-frequency (RF) channel containing the soundmodulation of the next lower channel.

adjacent video carrier In television, the radio-frequency (RF) carrier containing the picturemodulation of the next higher channel.

adjustable component Any circuit componentwhose main electrical value can be varied at will(e.g., a variable capacitor, inductor, resistor, orload).

adjustable instrument 1. An instrument whosesensitivity, range, or response can be varied atwill (e.g., multirange meter or wideband genera-tor). 2. An instrument that requires adjustmentor manipulation to measure a quantity (e.g.,bridge, potentiometer, or attenuator).

adjustable motor tuning An arrangement that al-lows the motor tuning of a receiver to be confinedto a portion of the frequency spectrum.

adjustable resistor A wirewound resistor in whichthe resistance wire is partially exposed to allowvarying the component’s value.

adjustable voltage divider A wirewound resistorwith terminals that slide on exposed resistancewire to produce various voltage values.

adjusted circuit A circuit in which leads that arenormally connected to a circuit breaker areshunted so that current can be measured undershort-circuit conditions without breaker trip-ping.

adjusted decibels Noise level (in decibels) above areference noise level (designated arbitrarily aszero decibels) measured at any point in a systemwith a noise meter that has previously been ad-justed for zero (at reference), according to specifi-cations.

address indirect An address that specifies a stor-age location that contains another address.

address memory The memory sections in a digitalcomputer that contain each individual register.

address modification In computer operations,altering only the address portion of an instruc-tion; if the command or instruction routine isthen repeated, the computer will go to the newaddress.

address part In a digital computer instruction, thepart of an expression that specifies the location.Also called ADDRESS FIELD.

address register In a computer, a register in whichan address is stored.

add/subtract time In a computer, the time re-quired to perform addition or subtraction, ex-cluding the time required to get the quantitiesfrom storage and to enter the sum or differenceinto storage.

add time In computer operations, the time re-quired to perform addition, excluding the time re-quired to get the quantities from storage and toenter the sum into storage.

a/d converter A device that changes an analogquantity into a digital signal. See ANALOG-TO-DIGITAL CONVERSION.

ADF Abbreviation of AUTOMATIC DIRECTIONFINDER.

ADI Abbreviation of ALTERNATE DIGIT INVER-SION.

adiabatic damping In an accelerator (see ACCEL-ERATOR, 1), reduction of beam size as beam en-ergy is increased.

adiabatic demagnetization A technique using amagnetic field to keep a substance at a low tem-perature, sometimes within a fraction of a degreeof absolute zero.

adjacency A character-recognition condition inwhich the spacing reference lines of two charac-ters printed consecutively in line are closer thanspecified.

adjacent- and alternate-channel selectivity Theselectivity of a receiver or radio-frequency (RF)amplifier, with respect to adjacent-channel andalternate-channel signals. That is, the extent towhich a desired signal is passed, and nearby un-wanted signals are rejected.

adjacent audio channel See ADJACENT SOUNDCHANNEL.

adjacent channel The channel (frequency band)immediately above or below the channel of in-terest.

adjacent-channel attenuation The reciprocal ofthe selectivity ratio of a radio receiver. The selec-tivity ratio is the ratio of the sensitivity of a re-ceiver (tuned to a given channel) to its sensitivityin an adjacent channel or on a specified numberof channels removed from the original.

adjacent-channel interference In television orradio reception, the interference from stationson adjacent channels. A common form arises

address indirect • adjusted decibels 15

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admittance Symbol, Y. Unit, siemens (formerlymho). The property denoting the comparativeease with which an alternating current flowsthrough a circuit or device. Admittance is the re-ciprocal of impedance (Z ): Y = 1/Z.

adp 1. Abbreviation of AMMONIUM DIHYDROGENPHOSPHATE, a piezoelectric compound used forsonar crystals. 2. Abbreviation of AUTOMATICDATA PROCESSING.

adsorption Adhesion of a thin layer of molecules ofone substance to the surface of another withoutabsorption. An example is adsorption of water tothe surface of a dielectric. This term is often con-fused with ABSORPTION because the spellings ofthe two words are almost identical. Compare AB-SORPTION.

adu Abbreviation of automatic dialing unit.advanced-class license An amateur-radio license

conveying all operating privileges, except for a fewsmall bands that are allocated to extra-class li-censees. The second-highest class of amateur li-cense.

advance information Data published prior to theactual production or availability of a manufac-tured component, circuit, or system. Advance in-formation is often only an approximate reflectionof the expected characteristics of a device.

advance wire A resistance wire used in thermo-couples and precision applications. It is an alloy ofcopper and nickel, which has high resistivity anda negligible temperature coefficient of resistance.

aeolight A glow lamp using a cold cathode and amixture of inert gases. Because its illuminationcan be regulated with an applied signal voltage, itis sometimes used as a modulation indicator formotion-picture sound recording.

aerial See ANTENNA.aerial cable A wire or cable run through the air, us-

ing support structures, such as towers or poles.aerodiscone antenna A miniature discone an-

tenna designed for use on aircraft.aerodynamics The science dealing with forces ex-

erted by air and other gases in motion—especiallyupon bodies (such as aircraft) moving throughthese gases.

aerogram See RADIOGRAM.aeromagnetic Pertaining to terrestrial magnetism,

as surveyed from a flying aircraft.aeronautical advisory station A civil defense and

advisory communications station in service forthe use of private aircraft stations.

aeronautical broadcasting service The specialservice that broadcasts information regarding airnavigation and meteorological data pertinent toaircraft operation.

aeronautical broadcast station A station of theaeronautical broadcasting service.

aeronautical fixed service A fixed radio servicethat transmits information regarding air naviga-tion and flight safety.

aeronautical fixed service station A station thatoperates in the aeronautical fixed service.

aeronautical ground station A land station thatprovides communication between aircraft andground stations.

aeronautical marker-beacon signal A distinctivesignal that designates a small area above a beacontransmitting station for aircraft navigation.

aeronautical marker-beacon station A land sta-tion that transmits an aeronautical marker-beacon signal.

aeronautical mobile service A radio service con-sisting of communications between aircraft, andbetween aircraft and ground stations.

aeronautical radio-beacon station An aeronauti-cal radio-navigation land station that transmitssignals used by aircraft and other vehicles to de-termine their position.

aeronautical radionavigation services Servicesprovided by stations transmitting signals used inthe navigation of aircraft.

aeronautical radio service A service that encom-passes aircraft-to-aircraft, aircraft-to-ground,and ground-to-aircraft communications impor-tant to the operation of aircraft.

aeronautical station A station on land, and occa-sionally aboard ship, operating in the aeronauti-cal mobile service.

Aeronautical Telecommunication Agency Theagency that administers the operation of stationsin the aeronautical radio service.

aeronautical telecommunications Collectively,all of the electronic and nonelectronic communi-cations used in the aeronautical service.

aeronautical utility land station A ground sta-tion in an airport control tower that providescommunications having to do with the control ofaircraft and other vehicles on the ground.

aeronautical utility mobile station At an airport,a mobile station that communicates with aero-nautical utility land stations and with aircraftand other vehicles on the ground.

aerophare See RADIO BEACON.aerospace 1. The region encompassing the earth’s

atmosphere and extraterrestrial space. 2. Per-taining to transport and travel in the earth’s at-mosphere and in outer space. This includesaircraft, orbiting space vessels, and interplane-tary spacecraft.

AES Abbreviation for Audio Engineering Society.AEW Abbreviation of airborne (or aircraft) early

warning.aF Abbreviation of ATTOFARAD.AF Abbreviation of AUDIO FREQUENCY.AFC 1. Abbreviation of AUTOMATIC FREQUENCY

CONTROL. 2. Abbreviation of AUDIO-FRE-QUENCY CHOKE.

affirmative In voice communications, a word oftenused for “yes”—especially when interference ispresent or signals are weak.

16 admittance • affirmative

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airborne intercept radar A type of short-rangeradar used aboard fighter and interceptor aircraftfor tracking their targets.

airborne long-range input Equipment aboard air-craft, for the purpose of facilitating the use oflong-range missiles.

airborne noise See ACOUSTIC NOISE.airborne radar platform Surveillance and alti-

tude-finding radar used aboard aircraft.air capacitor A capacitor in which air is the dielec-

tric between two sets of conductive plates. Alsocalled air-dielectric capacitor.

aircarrier aircraft station On an aircraft, a radiostation that is involved in carrying people for hireor in transporting cargo.

air cell A primary electrochemical cell in which thepositive electrode is depolarized by reduced oxy-gen in the air.

air cleaner See DUST PRECIPITATOR.air column The open space inside an acoustic

chamber, pipe, or horn.air-cooled component A component, such as a

power transistor, that is cooled by circulating air,compared with one cooled by a circulating liquid,such as water or oil.

air-cooled transistor A transistor (particularly apower transistor) from which the heat of opera-tion is drawn away, through radiation and con-vection, into the surrounding air. The transistoris usually mounted on a heatsink or fitted withfins.

air-cooled tube An electron tube from which heatis drawn away, mainly via convection, into thesurrounding air. A device called a chimney can beplaced around the tube, through which air isblown by a fan. Cool air enters through the bot-tom of the assembly, and hot air escapes from thetop.

air-core inductor A coil of wire wound around ahollow cylindrical form or in a loop, designed tointroduce inductive reactance into a circuit orsystem. In practice, the maximum attainable in-ductance is approximately 1 mH. This type of in-ductor is used in some wireless transmitters,receivers, and antenna networks. The componentcan be designed for high current-carrying capac-ity by using heavy-gauge wire and a large windingradius. The magnetic lines of flux extend consid-erably beyond the interior of the coil, especiallyalong the winding axis. This increases the likeli-hood of mutual inductance between the coil andsurrounding electrical components, devices, orcircuits.

air-core transformer A transformer without a fer-romagnetic core, so called because air is the onlymaterial at the center of (and immediately sur-rounding) the transformer coils.

aircraft bonding The practice of solidly connect-ing, for electrical purposes, the metal parts of anaircraft, including the engine.

AFIPS Acronym for American Federation of Infor-mation Processing Societies.

afpc Abbreviation of automatic frequency/phasecontrol.

AFSK Abbreviation of AUDIO-FREQUENCY-SHIFTKEYING.

afterglow The tendency of the phosphor of a cath-ode-ray-tube screen to glow for a certain time af-ter the cathode-ray beam has passed. Also seePERSISTENCE.

afterpulse An extraneous pulse in a multiplierphototube (photomultiplier), induced by a pre-ceding pulse.

AF transformer See AUDIO-FREQUENCY TRANS-FORMER.

a/g Abbreviation of AIR-TO-GROUND.AGC Abbreviation of AUTOMATIC GAIN CONTROL.AGE Abbreviation of AEROSPACE GROUND

EQUIPMENT.agent An active force, condition, mechanism, or

substance that produces or sustains an effect.Thus, a sudden voltage rise is a triggering agentin certain bistable circuits; arsenic is a dopingagent in semiconductor processing; the slow cool-ing of a heated metal to improve ductility is anANNEALING AGENT.

aging 1. An initial run of a component or circuitover a certain period of time shortly after manu-facture to stabilize its characteristics and per-formance. 2. The changing of electricalcharacteristics or of chemical properties over aprotracted period of time.

agonic line An imaginary line connecting points onthe earth’s surface at which a magnetic needleshows zero declination (i.e., points to true geo-graphic north).

AGREE Acronym for Advisory Group on Reliabilityof Electronics Equipment.

Ah Abbreviation of AMPERE-HOUR. Depending onthe standard used, the abbreviation can be amp-hr, a-h, a-hr, or A-h.

aH Abbreviation of ATTOHENRY.aided tracking In radar and fire control, a system

in which manual correction of target tracking er-ror automatically corrects the rate of movementof the tracking mechanism.

AIEE Abbreviation for American Institute of Electri-cal Engineers, now consolidated with the IRE,forming the IEEE.

AIP Abbreviation for American Institute of Physics.air The mixture of gases that constitutes the

earth’s atmosphere and figures prominently inthe manufacture and operation of numerouselectronic devices. By volume, air contains about21 percent oxygen, 78 percent nitrogen, andlesser amounts of argon, carbon dioxide, helium,hydrogen, krypton, neon, and xenon. It also con-tains varying amounts of water vapor, and insmoggy areas, carbon monoxide and the oxides ofsulfur and nitrogen.

AFIPS • aircraft bonding 17

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aircraft flutter Rapid, repetitive fading and inten-sifying of a received radio or television signal, re-sulting from reflections of the signal by passingaircraft.

aircraft station A nonautomatic radio communi-cations station installed on an aircraft.

air-dielectric coax A special type of COAXIAL CA-BLE designed to have minimum loss. The spacebetween inner and outer conductors is mostlyempty (i.e., air-filled). Some such cables aresealed and filled with an inert gas. The inner con-ductor is held away from the inner wall of theouter conductor by beads, washers, or a spiral-wound filament of high-grade dielectric material,such as polyethylene.

airport beacon A radio or light beacon that marksthe location of an airport.

airport control station A station that providescommunications between an airport controltower and aircraft in the vicinity.

airport surveillance radar An air-traffic-controlradar that scans the airspace within about 60miles (approximately 100 kilometers) of an air-port, and displays in the control tower the loca-tion of all aircraft below a certain altitude and allobstructions in the vicinity.

air-position indicator An airborne computer sys-tem that, using airspeed, aircraft heading, andelapsed time, furnishes a continuous indicationof the position of the aircraft. The indication isaffected by high-altitude winds. CompareGROUND-POSITION INDICATOR.

air-to-air communication Radio transmissionfrom one aircraft to another in flight. Com-pare AIR-TO-GROUND COMMUNICATION andGROUND-TO-AIR COMMUNICATION.

air-to-ground communication Radio transmis-sion from an aircraft in flight to a station locatedon the ground. Compare AIR-TO-AIR COMMUNI-CATION and GROUND-TO-AIR COMMUNICA-TION.

air-to-ground radio frequency The carrier fre-quency, or band of such frequencies, allocated fortransmissions from an aircraft to a ground sta-tion.

airwaves 1. Radio waves. The term is slang, but iswidely used. It probably came from the public’s

18 aircraft flutter • airwaves

air environment Pertaining to communicationsequipment aboard aircraft.

airflow The path or movement of air in, through, oraround an electronic device or piece of equip-ment—especially pertaining to an AIR-COOLEDCOMPONENT.

air gap 1. A narrow space between two parts of amagnetic circuit (e.g., the gap in the core of a fil-ter choke). Often, this gap is filled with a non-magnetic material, such as plastic, formechanical support. 2. The space between two ormore magnetically coupled or electrostaticallycoupled components. 3. A device that gets itsname from the narrow gap between two smallmetal balls, needle points, or blunt rod tipstherein. When an applied voltage is sufficientlyhigh, a spark discharges across the gap.

air/ground control radio station A station foraeronautical telecommunications related to theoperation and control of local aircraft.

air-insulated line 1. An open-wire feeder or trans-mission line. Typically, the line consists of twoparallel wires held apart by separators (bars orrods of high-grade dielectric material) situated atwide intervals. 2. AIR-DIELECTRIC COAX.

air-moving device A mechanical device, such as aspecially designed fan or blower, used to facilitateair cooling of electronic components.

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algebraic adder In computer operations, an adderthat provides the algebraic sum, rather than thearithmetic sum, of the entered quantities.

algebraic operation A form of electronic calculatoroperation, in which the keystrokes proceed in anintuitive sequence, following the way in which thecalculation is written down. Compare REVERSEPOLISH NOTATION.

algebraic sum The sum of two or more quantitieswith consideration of their signs. CompareARITHMETIC SUM.

algorithm A step-by-step procedure for solving aproblem, (e.g., the procedure for finding thesquare root of a number). It can be expressed in aline-by-line instruction set or as a flowchart.

algorithmic language A computer language usedto describe a numeral or algebraic process.

alias A label that is an alternate term for items ofthe same type; a label and several aliases canidentify the same data element in a computerprogram.

aliasing 1. In analog-to-digital (A/D) conversion, afalse output signal that results from a samplingrate that is too slow. Ideally, the sampling rate is atleast twice the highest input signal frequency. 2.Sawtooth-like irregularities, also called jaggies,which are sometimes introduced into a bit-mappedcomputer image when it is changed in size.

aliasing noise A form of signal distortion causedby a signal with an excessive bandwidth.

mistaken notion that radio signals are propa-gated by the air. 2. Skywaves.

Al Symbol for ALUMINUM.alabamine See ASTATINE.alacratized switch A mercury switch in which the

tendency of the mercury to stick to the parts hasbeen reduced.

alarm 1. An electronic security system. 2. A silentand/or audible alert signal transmitted by anelectronic security system when an intrusion oc-curs. 3. A silent and/or audible signal that in-forms personnel of the occurrence of anequipment malfunction.

alarm circuit A circuit that alerts personnel to asystem malfunction, a detected condition, or anintruder.

alarm condition 1. An intrusion or equipmentmalfunction that triggers an alarm circuit. 2. Theoperation of an alarm circuit that occurs in re-sponse to an intrusion or equipment malfunc-tion.

alarm hold A device that keeps an alarm soundingonce it has been actuated.

alarm output The signal sent from an alarm cir-cuit to a siren, buzzer, computer, or other exter-nal device to alert personnel to an ALARMCONDITION.

Documents

The Illustrated Dictionary of Electronics Illustrated...The Illustrated Dictionary of Electronics Eighth Edition Stan Gibilisco Editor-in-Chief McGraw-Hill New York Chicago San Francisco