. 2
( 42)


specially designed fan or blower, used to facilitate airwaves 1. Radio waves. The term is slang, but is
air cooling of electronic components. widely used. It probably came from the public™s
airwaves • aliasing noise

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 has
been reduced.
alarm 1. An electronic security system. 2. A silent
and/or audible alert signal transmitted by an
electronic security system when an intrusion oc-
curs. 3. A silent and/or audible signal that in-
forms personnel of the occurrence of an
equipment malfunction.
alarm circuit A circuit that alerts personnel to a
system malfunction, a detected condition, or an
alarm condition 1. An intrusion or equipment
malfunction that triggers an alarm circuit. 2. The
operation of an alarm circuit that occurs in re-
sponse to an intrusion or equipment malfunc-
alarm hold A device that keeps an alarm sounding
once 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 ALARM
alarm relay A relay that is actuated by an alarm
A-law A form of companding law frequently used in
European electronics (the mu-law is more often
used in North America). A nonlinear transfer algebraic adder In computer operations, an adder
characteristic in companding circuits. It can be that provides the algebraic sum, rather than the
continuous, or can be a piecewise linear approxi- arithmetic sum, of the entered quantities.
mation of a continuous function. algebraic operation A form of electronic calculator
A-law companded Companding by means of an 8- operation, in which the keystrokes proceed in an
bit binary code following the A-LAW, a specific intuitive sequence, following the way in which the
companding function. calculation is written down. Compare REVERSE
albedo For an unpolished surface, the ratio of re- POLISH NOTATION.
flected light to incident light. It can vary from 0.0 algebraic sum The sum of two or more quantities
to 1.0, or from 0 to 100 percent. with consideration of their signs. Compare
albedograph An instrument for measuring the ARITHMETIC SUM.
albedo of planets. algorithm A step-by-step procedure for solving a
ALC Abbreviation of AUTOMATIC LEVEL CON- problem, (e.g., the procedure for finding the
TROL. square root of a number). It can be expressed in a
alerting device An audible alarm that includes a line-by-line instruction set or as a flowchart.
self-contained solid-state audio oscillator. Pow- algorithmic language A computer language used
ered from the ac line or a battery, the device pro- to describe a numeral or algebraic process.
duces a raucous noise when actuated. alias A label that is an alternate term for items of
Alexanderson antenna A very-low-frequency the same type; a label and several aliases can
(VLF) and low-frequency (LF) vertically polarized identify the same data element in a computer
antenna, designed to minimize ground losses in program.
structures of manageable height. It usually con- aliasing 1. In analog-to-digital (A/D) conversion, a
sists of several wires, each quarter-wave reso- false output signal that results from a sampling
nant with a loading coil, and all connected rate that is too slow. Ideally, the sampling rate is at
together at the apex of a tower. The antenna is least twice the highest input signal frequency. 2.
fed between the ground and the base of one of Sawtooth-like irregularities, also called jaggies,
the wires. which are sometimes introduced into a bit-mapped
Alford antenna A loop antenna, in a square config- computer image when it is changed in size.
uration, with the corners bent toward the center aliasing noise A form of signal distortion caused
to lower the impedance at the current nodes. by a signal with an excessive bandwidth.
20 align • alloy diode

align 1. To adjust (i.e., to preset) the circuits of an Allen wrench A tool used to tighten or loosen an
electronic system, such as a receiver, transmit- Allen screw. It is a hexagonal rod and is available
ter, or test instrument, for predetermined re- in various sizes.
sponse. 2. To arrange elements in a certain
precise orientation and spacing, relative to each
other, as in a Yagi antenna. 3. To orient antennas
so that they are in line of sight, with respect to
each other.
alignment The process of ensuring that equip-
ment, components, or systems are adjusted, both
physically and electronically, for the most effi-
cient possible performance.
alignment chart A line chart for the simple solu-
tion of electronic problems. It is so called because
its use involves aligning numerical values on var-
ious scales, the lines intersecting at the solution
on another scale. Also called nomograph. alligator clip A spring-loaded clip with jagged
alignment pin A pin or protruding key, usually in teeth, designed to be used for temporary electri-
the base of a removable or plug-in component, to cal connections.
ensure that the latter will be inserted correctly allocate 1. To assign (especially through legisla-
into a circuit. Often, the pin mates with a keyway, tion) operating frequencies or other facilities or
notch, or slot. conditions needed for scientific or technical activ-
alignment tool A specialized screwdriver or ity; see, for example, ALLOCATION OF FRE-
wrench (usually nonmagnetic) used to adjust QUENCIES. 2. In computer practice, to assign
padder or trimmer capacitors or inductor cores. locations in the memory or registers for routines
alive See LIVE. and subroutines.
alkali See BASE, 2. allocated channel A frequency channel assigned
alkali metals Metals whose hydroxides are bases to an individual or group.
(alkalis). The group includes cesium, francium, allocated-use circuit 1. A circuit in which one or
lithium, potassium, rubidium, and sodium. more channels have been authorized for the ex-
alkaline battery 1. A battery composed of alkaline clusive use of one or more services. 2. A commu-
cells and characterized by a relatively flat dis- nications link assigned to users needing it.
charge curve under load. allocation of frequencies See RADIO SPECTRUM.
alkaline cell A common non-rechargeable electro- allocator A telephone system distributor associ-
chemical cell that employs granular zinc for ated with the finder control group relay assembly.
the negative electrode, potassium hydroxide as It reserves an inactive line-finder for another call.
the electrolyte, and a device called a polarizer as allophone A variation in the sound of a phoneme,
the positive electrode. Produces approximately depending on what comes before and/or after the
1.5 volts under no-load conditions. The geometry phoneme in the course of speech. Important in
of construction is similar to that of the zinc“ speech recognition and synthesis. There are 128
carbon cell, but it can deliver current effectively different phoneme variations in the English lan-
at lower temperatures. Cells of this type have guage. See PHONEME.
shelf lives longer than zinc“carbon cells; they also alloter relay A telephone system line-finder relay
have greater energy-storage capacity per unit that reserves an inactive line-finder for the next
volume, but they are more expensive than zinc“ incoming call from the line.
carbon cells. They are used in calculators, tran- allotropic Pertaining to a substance existing in
sistor radios, and cassette tape and compact-disc two forms.
players. Compare ZINC“CARBON CELL. alloy A metal that is a mixture of several other met-
alkaline-earth metals The elemental metals bar- als (e.g., brass from copper and zinc), or of a
ium, calcium, strontium, and sometimes beryl- metal and a nonmetal.
lium, magnesium, and radium, some of which are alloy deposition In semiconductor manufacture,
used in vacuum tubes. depositing an alloy on a substrate.
alkaline earths Substances that are oxides of the alloy-diffused transistor A transistor in which the
alkaline-earth metals. Some of these materials base is diffused and the emitter is alloyed. The
are used in vacuum tubes. collector is provided by the semiconductor sub-
all-diffused A type of INTEGRATED CIRCUIT in strate into which alloying and diffusion are
which both active and passive elements have affected. Compare ALLOY TRANSISTOR and
been fabricated by diffusion and related pro- DIFFUSE TRANSISTOR.
cesses. alloy diode A junction-type semiconductor diode
Allen screw A screw fitted with a six-sided (hexag- in which a suitable substance (such as p-type) is
onal) hole. alloyed into a chip of the opposite type (such as
alloy diode • alternating-charge characteristic

n-type) to form the junction. Also called alloy- alphabetic-numeric Also called alphabetical-
junction diode. numerical and alphanumeric. In computer opera-
alloy junction In a semiconductor device, a posi- tions, pertaining to letters of the alphabet and
tive/negative (pn) junction formed by alloying a special characters, and to numerical digits.
suitable material (such as indium) with the semi- alpha cutoff frequency Also called alpha cutoff. In
conductor (silicon or germanium). a bipolar transistor circuit, the frequency at
alloy transistor A transistor whose junctions are which the alpha (current gain) becomes 0.707
created by alloying. Also see ALLOY JUNCTION. (70.7 percent) of its value at 1 kHz. A bipolar
transistor can have considerable gain at its alpha
cutoff. This specification denotes how rapidly a
transistor loses gain as the frequency increases,
an important consideration in the design of radio-
frequency (RF) amplifiers. See ALPHA. Compare
alpha decay The decay of a substance in which the
nuclei of the atoms emit alpha particles, resulting
in a change of the atomic number and atomic
weight of the substance over a period of time.
alphanumeric See ALPHABETIC-NUMERIC.
all-pass filter Also called all-pass network. A filter alphanumeric code In computer operations or in
that (ideally) introduces a desired phase shift or communications, a code composed of, or using,
time delay, but has zero attenuation at all fre- both letters and numbers.
quencies. alphanumeric readout A type of digital readout
all-relay central office In telephone service, an that displays both letters and numerals.
automatic central-office switchboard that uses alpha particle A nuclear particle bearing a positive
relay circuits to make line interconnections. charge. Consisting of two protons and two neu-
all-wave Pertaining to a wide operating-frequency trons, it is given off by certain radioactive sub-
range. Few systems are literally all-wave. For ex- stances. Compare BETA RAYS and GAMMA RAYS.
ample, a so-called “all-wave radio receiver” might alpha system An alphabetic code-signaling sys-
cover 500 kHz to 30 MHz only. tem.
all-wave antenna An antenna that can be operated alphatron An ionizing device in which the radia-
over a wide frequency range with reasonable effi- tion source is an emitter of alpha particles.
ciency and preferably without needing readjust- alteration An inclusive-OR operation.
ment. Examples are the DISCONE ANTENNA and alternate channel In communications, a channel
the LOG-PERIODIC ANTENNA. situated two channels higher or lower than a
all-wave generator A signal generator that will given channel. Compare ADJACENT CHANNEL.
supply output over a wide range of frequencies. alternate-channel interference Interference
all-wave receiver A radio receiver that can be caused by a transmitter operating in the chan-
tuned over a very wide range of frequencies, such nel beyond an adjacent channel. Compare
allyl plastics Plastics, sometimes used as dielectrics alternate digit inversion In multiplex equipment,
or for other purposes in electronics, based on a method of switching the binary signals to the
resins made by polymerization of monomers (such opposite state, in accordance with A-law com-
as diallyl phthalate) that contain allyl groups. panding.
alnico Coined from the words aluminum, nickel, alternate frequency A frequency allocated as an
and cobalt. An alloy used in strong permanent alternative to a main assigned frequency and
magnets, it contains the constituents noted plus used under certain specified conditions.
(sometimes) copper or titanium. alternate-mark inversion signal A signal that
alpha 1. Symbol, ±. The current gain of a common- conveys bits in which the successive signals are
base-connected bipolar transistor. It is the ratio of of opposite polarity (positive, then negative, then
the differential of collector current to the differen- positive, etc.). They are equal in absolute value
tial of emitter current; ± = dIC/dIE. For a junction amplitude.
transistor, alpha is always less than unity, but alternate mode The technique of displaying sev-
very close to it. 2. In voice communications, the eral signals on an oscilloscope screen by rapidly
phonetic representation of the letter A. switching the signals in sequence at the end of
alphabet The set of all characters in a natural lan- each sweep.
guage. alternate routing A secondary, or backup, com-
alphabetic coding In computer practice, an abbre- munications path, used when primary (normal)
viation system for coding information to be fed routing is impossible.
into the computer. The coding contains letters, alternating-charge characteristic In a nonlinear
words, and numbers. capacitor, the relationship between the instanta-
22 alternating-charge characteristic • amateur extra-class license

neous charge and the instantaneous value of an above the earth™s surface. 3. The angle, measured
alternating voltage. in degrees, with respect to the horizon, at which a
alternating current Abbreviation, ac. A current that highly directional antenna is pointed.
periodically reverses its direction of flow. In one cy- altitude delay In a plan-position-indicating type of
cle, an alternation starts at zero, rises to a maxi- radar, the sync delay introduced between trans-
mum positive level, returns to zero, rises to a mission of the pulse and start of the trace on the
maximum negative level, and again returns to zero. indicator screen to eliminate the altitude circle in
The number of such cycles completed per second is the display.
termed the ac frequency. Also see CURRENT. ALU Abbreviation of ARITHMETIC AND LOGIC
alternating-current continuous wave An ampli- UNIT.
tude-modulated signal resulting from the opera- alumel An alloy used in the construction of one
tion of an oscillator or RF amplifier with raw ac type of THERMOCOUPLE. It is composed of
voltage. nickel (three parts) and aluminum (one part).
alternating current/direct current See AC/DC. alumina An aluminum-oxide ceramic used in elec-
alternating-current erasing head See AC ERAS- tron tube insulators and as a substrate in the
ING HEAD. fabrication of thin-film circuits.
alternating-current pulse A short-duration ac aluminum Symbol, Al. An elemental metal. Atomic
wave. number, 13. Atomic weight, 26.98. Aluminum is
alternating-current transmission 1. The propa- widely used in electronics, familiar instances be-
gation of alternating currents along a length of ing chassis, wire, shields, semiconductor doping,
conductor”especially for power-transfer pur- and electrolytic-capacitor plates.
poses. 2. A means of picture transmission in aluminum antimonide Formula, AlSb. A crystalline
which a given signal strength produces a con- compound useful as a semiconductor dopant.
stant value of brightness for a very short time. aluminized screen A television picture-tube
alternating voltage Also called alternating-current screen with a thin layer of aluminum deposited
voltage. See AC VOLTAGE. on its back to brighten the image and reduce ion-
alternation In ac practice, a half cycle. In a complete spot formation.
cycle, there are two alternations, one in the positive Am Symbol for AMERICIUM.
direction and one in the negative direction. A/m Abbreviation of ampere per meter: the SI unit
of magnetic field strength.
AM 1. Abbreviation of amplitude modulator. 2. Ab-
amalgam An alloy of a metal and mercury. Loosely,
any combination of metals.
amateur 1. A nonprofessional, usually noncom-
mercial devotee of any technology (i.e., a hobby-
ist). 2. A licensed radio operator legally
authorized to operate a station in the AMATEUR
amateur band Any band of radio frequencies as-
signed for noncommercial use by licensed radio
amateurs (see AMATEUR, 2). In the United
States, numerous such bands are above 1.8 MHz
(160 meters). Also see AMATEUR SERVICE and
amateur call letters Call letters assigned by a gov-
ernment licensing authority”especially to ama-
teur stations. Call-letter combinations consist of
a letter prefix denoting the country in which the
station is situated, plus a number designating
alternative denial A NOT-AND operation. the location within the country, and two or more
alternator Any mechanically driven machine for letters identifying the particular station. For ex-
generating ac power. Sometimes specifically one ample: W6ABC: W (or K) = United States, 6 = Cal-
having a permanent-magnet rotor, such as a ifornia, and ABC = identification of individual
magneto. licensee (issued alphabetically, except under spe-
altimeter station An airborne transmitter whose cial circumstances).
signals are used to determine the altitude of air- amateur callsign See AMATEUR CALL LETTERS.
craft. amateur extra-class license The highest class of
altitude 1. The vertical distance of an object above amateur-radio operator license in the United
sea level. 2. The vertical distance of an object States. It conveys all operating privileges.
amateur radio • AM/FM tuner

amateur radio 1. A general term, referring to the will cause no malfunction of, or damage to, a cir-
practice of operation, experimentation, and other cuit or device.
work in and related to the amateur service. 2. The ambiguity 1. Any unclear, illogical, or incorrect in-
hardware that comprises an amateur radio sta- dication or result. 2. The seeking of a false null by
tion. 3. A radio receiver, transmitter, or transceiver a servo. 3. In digital computer operations, an er-
that is specifically designed for operation in the ror resulting from improper design of logic.
amateur bands. ambiguous count In digital counters, a clearly in-
amateur radio operator Also called radio ham or correct count. See ACCIDENTAL TRIGGERING.
ham radio operator. An individual licensed to ambisonic reproduction A close approximation of
transmit radio signals in the amateur service. the actual directional characteristics of a sound in
amateur service A two-way radio service, existing a given environment. The reproduced sound al-
purely for hobby purposes (i.e., without pecu- most exactly duplicates the sound in the actual
niary interest). environment in which it was recorded.
amateur station A radio station licensed in the American Morse code (Samuel F. B. Morse, 1791“
AMATEUR SERVICE. 1872). Also called Railroad Morse. A telegraph
amauroscope An electronic aid to the blind, in code, at one time used on wire telegraph lines in
which photocells in a pair of goggles receive light the United States. It differs from the Continental
images. Electric pulses proportional to the light code, also called the International Morse Code,
are impressed upon the visual receptors of the which is used in radiotelegraphy. Compare CON-
brain through electrodes in contact with nerves TINENTAL CODE.
above each eye. American National Standards Institute Ac-
amber A yellow or brown fossil resin that is histor- ronym, ANSI. An industrial group in the United
ically important in electronics. It is the first mate- States that encourages companies to manufac-
rial reported to be capable of electrification by ture devices and equipment in accordance with
rubbing (Thales, 600 BC). Also, the words elec- certain standards. The objective is to minimize
tricity, electron, and electronics are derived from hardware incompatibility problems.
the Greek name for amber, elektron. American Radio Relay League A worldwide orga-
ambience The acoustic characteristic of a room, in nization of amateur radio operators, headquar-
terms of the total amount of sound reaching a lis- tered in Newington, Connecticut. The official
tener from all directions. publications are the monthly magazines, QST
ambient An adjective meaning “surrounding.” Often and QEX. They also publish numerous books and
used as a noun in place of the adjective-noun com- other educational materials.
bination (thus, “10 degrees above ambient,” in- American Standards Association Abbreviation,
stead of “10 degrees above ambient temperature”). ASA. At one time, the name of the national associ-
ambient humidity The amount of moisture in the ation in the U.S. devoted to the formation and dis-
air at the time of measurement or operations in semination of voluntary standards of dimensions,
which dampness must be accounted for. performance, terminology, etc. See ANSI.
ambient level The amplitude of all interference American wire gauge Abbreviation, AWG. Also
(acoustic noise, electrical noise, illumination, called Brown and Sharpe gauge or B & S gauge.
etc.) emitted from sources other than that of a The standard American method of designating
signal of interest. wire sizes. Wire is listed according to gauge num-
ambient light Also called ambient illumination. ber from 0000 (460 mils diameter) to 40 (3.145
Room light or outdoor light incident to a location mils diameter).
at the time of measurement or operations. americium Symbol, Am. A radioactive elemental
ambient-light filter In a television receiver, a filter metal first produced artificially in the 1940s.
mounted in front of a picture-tube screen to min- Atomic number, 95. Atomic weight, 243.
imize the amount of ambient light reaching the AM/FM receiver A radio set that can receive either
screen. amplitude-modulated or frequency-modulated
ambient noise 1. In electrical measurements and signals. Usually, a band switch incorporates the
operation, background electrical noise. 2. In demodulation-selection circuitry so that as the
acoustical measurements and operations, audi- frequency range is changed, the appropriate de-
ble background noise. tector is accessed.
ambient pressure Surrounding atmospheric pres- AM/FM transmitter A radio transmitter whose
sure. output signal can be frequency- or amplitude-
ambient temperature The temperature surround- modulated by a panel selector switch.
ing apparatus and equipment (e.g., room temper- AM/FM tuner A compact radio receiver unit that
ature). can handle either amplitude- or frequency-
ambient-temperature range 1. The range over modulated signals, and delivers low-amplitude
which ambient temperature varies at a given lo- output to a high-fidelity audio power amplifier.
cation. 2. The range of ambient temperature that Compare AM TUNER and FM TUNER.
24 AMI • Amperian whirl

ammeter-voltmeter method The determination of
Character Symbol Character Symbol
resistance or power values from the measure-
A .” U ..”
ment of voltage (E) and current (I ). For resistance,
B ”... V ...”
R = E/I; for power, P = EI.
C .. . W .””
ammonium chloride Formula, NH4Cl. The elec-
D ”.. X .”..
trolyte in the carbon-zinc type of primary cell.
E . Y .. ..
Also called SAL AMMONIAC.
F .”. Z ... .
G ””. 1 .””.
H . ... 2 ..”..
amortisseur winding 1. A winding that acts
I .. 3 ...”.
against pulsation of the magnetic field in an elec-
J ”.”. 4 ....”
tric motor. 2. A winding that acts to prevent os-
K ”.” 5 ””” cillation in a synchronous motor.
L 6 ......
”” amorphous substance A noncrystalline material.
M 7 ””..
”” amp 1. Slang for AMPERE. 2. Slang for AMPLIFIER”
N ”. 8 ”.... especially in audio high-fidelity applications.
O .. 9 ”..” ampacity Current-carrying capacity expressed in
P ..... 0 amperes.
Q ..”. period ..””.. amperage The strength of an electric current (i.e.,
the number of amperes).
R . .. comma .”.”
ampere (Andre Marie Ampere, 1775-1836). Abbrevi-
S ... question ”..”.
ations, A (preferred), a, amp. The SI base unit of
T mark

current intensity (I ). The ampere is the constant
current that, if maintained in two straight parallel
conductors of infinite length and of negligible cir-
cular cross section and placed 1 meter apart in a
American Wire Gauge (AWG) Diameters vacuum, would produce between the conductors a
force of 2 — 10 “7 newton per meter. One ampere
AWG Millimeters Inches
AWG Millimeters Inches
flows through a 1-ohm resistance when a potential
21 0.723 0.0285
1 7.35 0.289 of 1 volt is applied; thus I = E/R. Also see MI-
22 0.644 0.0254
2 6.54 0.257
23 0.573 0.0226
3 5.83 0.230
ampere balance A device consisting of two con-
24 0.511 0.0201
4 5.19 0.204
ductors in which the force between them (caused
25 0.455 0.0179
5 4.62 0.182
by current) is balanced against the gravitational
26 0.405 0.0159
6 4.12 0.163
force exerted on an object in the gravitational
27 0.361 0.0142
7 3.67 0.144 field of the earth. Used for the precise determina-
28 0.321 0.0126
8 3.26 0.128 tion of current of large dimension, or of the size of
the ampere.
29 0.286 0.0113
9 2.91 0.115
ampere-hour Abbreviations: Ah, amp-hr. The
30 0.255 0.0100
10 2.59 0.102
quantity of electricity that passes through a cir-
31 0.227 0.00894
11 2.31 0.0909
cuit in one hour when the rate of flow is one am-
32 0.202 0.00795
12 2.05 0.0807
pere. Also see BATTERY CAPACITY.
33 0.180 0.00709
13 1.83 0.0720
ampere-hour meter An instrument for measuring
34 0.160 0.00630
14 1.63 0.0642 ampere-hours. It contains a small motor driven by
35 0.143 0.00563
15 1.45 0.0571 the current being measured and which moves a
36 0.127 0.00500
16 1.29 0.0508 point on an ampere-hour scale. The motor speed is
proportional to the current. The position of the
37 0.113 0.00445
17 1.15 0.0453
pointer is proportional to current and elapsed time.
38 0.101 0.00398
18 1.02 0.0402
Ampere™s law Current flowing in a wire generates
39 0.090 0.00354
19 0.912 0.0359
a magnetic flux that encircles the wire in the
40 0.080 0.00315
20 0.812 0.0320
clockwise direction when the current is moving
away from the observer.
ampere-turn Symbol, NI. A unit of magnetomotive
A-minus Also, A-. The negative terminal of an A
force equal to 1 ampere flowing in a single-turn
battery, or pertaining to the part of a circuit con-
coil. The ampere-turns value for any coil is ob-
nected to that terminal.
tained by multiplying the current (in amperes) by
ammeter An instrument used to measure the
the number of turns in the coil.
amount of current (in amperes) flowing in a circuit.
Amperian whirl The stream of electrons in a
ammeter shunt A resistor connected in parallel with
single-turn, current-conducting wire loop acting
an ammeter to increase its current range. Also see
as an elementary electromagnet.
amp-hr • amplify

tical. 2. The number of decibels by which an AM-
Direction of
PLIFIER circuit increases the amplitude of a sig-
nal. For voltage or current, this figure has
flux flow
meaning only when the input and output
impedances are identical. See DECIBEL. 3. The
ALPHA or BETA of a bipolar transistor. 4. In
the operation of an electron tube, the ratio of
the derivative (instantaneous rate of change) of
the plate voltage to the derivative of the grid volt-
age, for zero change in plate current.
amplified ALC Abbreviation, AALC. An automatic-
level-control (ALC) system that uses the amplifi-
cation of the fed-back control signal. It is used in
RF power amplifiers, particularly single-sideband
Direction (SSB) linear amplifiers, to prevent overmodula-
of current tion and nonlinearity.
amplified back bias A declining voltage developed
across a fast-time-constant circuit in an amplifier
stage and fed back into a preceding stage.
Ampere™s Law
amplifier Any device that increases the magni-
tude of an applied signal. It receives an input
signal and delivers a larger output signal that, in
amp-hr One style of abbreviating AMPERE-HOUR. addition to its increased amplitude, is a replica
Also, Ah. of the input signal. Also see CURRENT AMPLI-
amplidyne A dynamo-like rotating dc machine FIER, POWER AMPLIFIER, and VOLTAGE AM-
that can act as a power amplifier because the re- PLIFIER.
sponse of the output voltage to changes in field amplifier diode Any semiconductor that can pro-
excitation is quite rapid. Used in servo systems. vide amplification in a suitable circuit or mi-
crowave system. See DIODE AMPLIFIER.
amplifier distortion A change in the waveform of a
signal, arising within an amplifier that is oper-
ated in compliance with specified conditions.
amplifier input 1. The terminals and section of an
amplifier that receive the signal to be amplified.
2. The signal to be amplified.
amplifier noise Collectively, all extraneous signals
present in the output of an amplifier when no
working signal is applied to the amplifier input
amplifier nonlinearity A condition in which the
amplifier output signal does not exhibit a linear
relationship to the corresponding input signal.
Some amplifiers are designed to operate in a lin-
ear manner at all times, but many amplifier types
need not function in this manner to be effective.
amplification 1. The process of increasing the
magnitude of a signal. This entails an input sig-
nal controlling a local power supply to produce a
amplifier output 1. The terminals and section of
larger output signal. Depending on the kind of in-
an amplifier that deliver the amplified signal for
put and output signals, amplification can be cat-
external use. 2. The amplified signal.
egorized as CURRENT, VOLTAGE, POWER, or
amplifier power The power level of the output sig-
some combination of these. 2. The qualitative sig-
nal delivered by an amplifier (also called OUTPUT
nal increase resulting from the process in 1. 3.
POWER), or the extent to which the amplifier in-
The quantitative signal increase (resulting from
creases the power of the input signal (also called
the process in 1), expressed as a factor (such as
100) or in terms of decibels (dB). See AMPLIFICA-
amplifier response The performance of an ampli-
fier throughout a specified frequency band. Fac-
amplification factor 1. The ratio of the output
tors usually included are gain, distortion,
voltage, current, or power to the input voltage,
amplitude versus frequency, and power output.
current, or power of an AMPLIFIER circuit. For
amplify To perform the functions of amplification
voltage or current, this ratio has meaning only
when the input and output impedances are iden-
26 amplifying delay line • amplitude selection

amplifying delay line A delay line that causes am- munications and broadcasting. The modulating-
plification of signals in a circuit intended for signal energy appears at sideband frequencies
pulse compression. above and below, and very close to, the carrier
amplistat A self-saturating magnetic amplifier. frequency. These sideband signals carry all the
amplitron A backward-wave amplifier used in mi- information. The extent of modulation is ex-
crowave circuits. pressed as a percentage, from 0, which represents
amplitude The extent to which an alternating or an unmodulated carrier, to 100, which repre-
pulsating current or voltage swings, positively sents full modulation. In a signal modulated 100
and negatively, from zero or from a mean value. percent, one-third of the power is used to convey
amplitude-controlled rectifier A thyratron- or the data; the other two-thirds is consumed by the
thyristor-based rectifier circuit. carrier. This form of modulation is essentially
amplitude density distribution A mathematical outmoded, although it is still used in the stan-
function giving the probability that, at a given in- dard broadcast band from 535 to 1605 kHz. See
stant in time, a fluctuating voltage has a certain FREQUENCY MODULATION, PHASE MODU-
amplitude distortion In an amplifier or network,
the condition in which the output-signal ampli-
tude exhibits a nonlinear relationship to the in-

put-signal amplitude.
amplitude error 1. The error in measuring the am-

plitude of a signal, normally expressed as a per-
centage of signal amplitude or as a percentage of
full scale. 2. The frequency at which the output
amplitude of a signal is in error by 1% with am-
plitude at 10% of full scale.
amplitude factor For an ac wave, the ratio of the
peak value to the rms value. The amplitude factor
of a sine wave is equal to the square root of 2 =

amplitude fading In the propagation of electro-
magnetic waves, a condition in which the ampli-
tudes of all components of the signal (i.e., carrier
and sidebands) increase and decrease uniformly.
amplitude/frequency response Performance of
an amplifier throughout a specified range, as ex-
hibited by a plot of output-signal amplitude ver-
sus frequency for a constant-amplitude input
amplitude gate A transducer that transmits only
those portions of an input wave that lie within
two close-spaced amplitude boundaries; also
called slicer. amplitude-modulation noise Spurious amplitude
amplitude limiter A circuit, usually with auto- modulation of a carrier wave by extraneous sig-
matic gain control (AGC), that keeps an amplifier nals and random impulses, rather than by the in-
output signal from exceeding a certain level, de- tended data-containing signal.
spite large variations in input-signal amplitude. A amplitude noise In radar, amplitude fluctuations
dc-biased diode performs passive limiting action of an echo returned by a target. This noise limits
via clipping. the precision of the system.
amplitude-modulated generator A signal genera- amplitude of noise The level of random noise in a
tor whose output is amplitude modulated. Usu- system. The amplitude of noise is measured in
ally, this instrument is an RF generator that is the same way that signal amplitude is measured.
modulated at an audio frequency. amplitude range The maximum-to-minimum am-
amplitude-modulated transmitter A radio- plitude variation of a signal. It can be expressed
frequency transmitter whose carrier is varied in as a direct numerical ratio or in decibels.
amplitude, according to the rate of change of amplitude response The maximum output obtain-
some data-containing signal (such as voice, mu- able at various frequencies over the range of an
sic, facsimile, television pictures, control signals, instrument operating under rated conditions.
or instrument readings). amplitude selection The selection of a signal, ac-
amplitude modulation Abbreviation, AM. A cording to its correspondence to a predetermined
method of conveying intelligence in wireless com- amplitude or amplitude range.

amplitude separator • analog integrator

an output equal to their sum or difference (in any
amplitude separator In a television receiver, a cir-
combination), as desired.
cuit that separates the control pulses from the
analog channel In an ANALOG COMPUTER, an in-
composite video signal.
formation channel in which the extreme limits of
amplitude suppression ratio The ratio of an un-
data magnitude are fixed, and the data can have
desired output of a frequency-modulated (FM) re-
any value between the limits.
ceiver to the desired output, when the test signal
analog communications Any form of communica-
is amplitude modulated and frequency modu-
tions in which a carrier, generally an electromag-
lated simultaneously.
netic wave or high-frequency current, is varied in
amplitude-versus-frequency distortion Distortion
a continuous and controlled way by a data-
resulting from varying gain or attenuation of an
containing signal. See ANALOG, 2.
amplifier or network, with respect to signal fre-
analog computer A computer in which input and
output quantities are represented as points on
AMTOR A form of amateur-radio data communica-
continuous (or small-increment) scales. To repre-
tions, in which the accuracy of a group of charac-
sent these quantities, the computer uses voltages
ters in a message is checked periodically by the
or resistances that are proportional to the num-
receiving station. If an error appears likely, then
bers to be worked on. When the quantities are
the receiving station sends an instruction to the
nonelectrical (such as pressure or velocity), they
transmitting station to retransmit that particular
are made analogous by proportional voltages or
group of characters. Characters are sent in
bunches with pauses for possible inquiries from
analog data 1. Data represented in a quantita-
the receiving station.
tively analogous way. Examples are the deflection
AM tuner A compact radio receiver unit that han-
of a movable-coil meter, the positioning of a slider
dles amplitude-modulated signals and delivers
on a slide rule, and the setting of a variable resis-
low-amplitude audio output to a high-fidelity am-
tor to represent the value of a nonelectrical quan-
plifier. Compare AM/FM TUNER and FM TUNER.
tity. Also see ANALOG. 2. Data displayed along a
amu Abbreviation of atomic mass unit.
smooth scale of continuous values (as by a
amusement robot An electromechanical robot, of-
movable-coil meter), rather than in discrete steps
ten computer-controlled, that is intended for use
(as by a digital meter).
as a toy.
analog differentiator An analog circuit or device
AN- A prefix designator used by American military
whose output waveform is the derivative of the
services to indicate commonality.
input-signal waveform, with respect to time.
anacoustic Pertaining to the lack of sound or ab-
sence of reverberation or transmission of sonic
analog 1. A quantity that corresponds, point for
point or value for value, to an otherwise unrelated
quantity. Thus, voltage is the analog of water
pressure, and current is the analog of water flow.
2. Varying over a continuous range and, there-
fore, capable of attaining an infinite number of
values or levels. Compare DIGITAL.
analog adder An analog circuit or device that re-
ceives two or more inputs and delivers an output
equal to their sum.
analog adder/subtracter An analog circuit or de-
vice that receives two or more inputs and delivers

analog divider An analog circuit or device that re-
ceives two inputs and delivers an output equal to
their quotient.
analog electronics Electronic techniques and
equipment that is based on uniformly changing
signals, such as sine waves, and often having
continuous-scale indicators, such as D™Arsonval
analog information Approximate numerical infor-
mation, as opposed to digital information, which
is assumed to be exact.
analog integrator An analog circuit or device
whose output waveform is the integral of the in-
put signal waveform, with respect to time.
28 analog inverting adder • AND circuit

that produces an analog record. The counterpart
is a digital recorder, which produces a readout in
discrete numbers (printed or visually displayed).
analog representation Representation of informa-
tion within a smooth, continuous range, rather
than as separate (discrete) steps or points.
analog signal A signal that attains an infinite
number of different amplitude levels, as opposed
to one that can attain only a finite number of lev-
els as a function of time.
analog subtracter An analog circuit or device that
receives two inputs and delivers an output equal
to their difference.
analog summer See ANALOG ADDER.
analog switch A switching device that will only
analog inverting adder An analog adder that de-
pass signals that are faithful analogs of trans-
livers a sum with the opposite sign to that of the
ducer parameters.
input quantities.
analog-to-digital conversion 1. A process in
analog meter An indicating instrument that uses
which an analog signal (such as a voice wave-
a movable-coil arrangement or the equivalent,
form) is changed into a digital or binary signal
causing a rotating pointer to indicate a particular
that conveys the same information. This process
value on a graduated printed scale. Compare
is commonly used in digital computers to encode
sounds and images. It is also used in communi-
cations systems to improve efficiency, minimize
the necessary bandwidth, and optimize the sig-
nal-to-noise ratio. 2. A process in which continu-
ous mechanical motion is encoded into a digital
or binary electronic signal.
analog-to-digital converter Any circuit or device
analysis 1. The rigorous determination of the con-
stants and modes of operation for electronic
equipment. Compare SYNTHESIS. 2. A branch of
mathematics dealing with point sets, relations,
and functions.
analytical engine A primitive mechanical calculat-
ing machine, invented in 1833 by Charles Bab-
analog multiplexer 1. A multiplexer used with
analyzer 1. Any instrument that permits analysis
analog signals (see MULTIPLEXER). 2. An analog
through close measurements and tests (e.g., dis-
time-sharing circuit.
tortion analyzer, WAVE ANALYZER, or gas ana-
analog multiplier An analog circuit or device that
lyzer). 2. A computer program used for debugging
receives two or more inputs and delivers an out-
purposes; it analyzes other programs and sum-
put equal to their product.
marizes references to storage locations. 3. An
analog network A circuit that permits mathemati-
analysis interface to an oscilloscope.
cal relationships to be shown directly by electric
anastigmatic yoke Also called full-focus yoke. In a
or electronic means.
television (TV) receiver, a deflection yoke with a
analogous pole In a PYROELECTRIC MATERIAL,
cosine winding for better focus at the edges of the
the end or face having the positive electric charge.
analog output An output quantity that varies
anchorage In plastic recording tape, the adhesion
smoothly over a continuous range of values,
of the magnetic oxide coating to the surface of the
rather than in discrete steps.
analog record Also called analog recording. A
ancillary equipment Equipment that does not di-
record or recording method in which some prop-
rectly enter into the operation of a central system.
erty of the recorded material, such as displace-
Examples are input/output components of a com-
ment or magnetization, varies over a continuous
puter and test instruments attached to a system.
range that is relative to time and/or physical po-
AND circuit In digital systems and other switching
circuits, a logic gate whose output is high (logic 1)
analog recorder Any recorder, such as a recording
only when all input signals are high. Otherwise
oscillograph, potentiometric recorder, electroen-
the output is low (logic 0). Compare OR CIRCUIT.
cephalograph, electrocardiograph, or lie detector,
Anderson bridge • angle of beam

anechoic chamber An enclosure that does not re-
Anderson bridge An ac bridge circuit with six flect sound waves that approach its walls. Such a
impedances, permitting the value of an unknown chamber is used to test certain audio devices.
inductance to be determined in terms of a stan- anemograph An electromechanical device that
dard capacitance. produces a recording of wind speed versus time.
Generally, it consists of an ANEMOMETER con-
nected to a PEN-AND-INK RECORDER via a suit-
able electronic interface.
anemometer An instrument that measures or
indicates wind speed, or speed and direction (ve-
angel 1. An extraneous image, usually of short du-
ration, on a cathode-ray-tube (CRT) display. The
term applies particularly to anomalies in a radar
image caused by low-atmospheric reflection,
birds, or other mobile objects. 2. Air-deployed
metallic debris, also known as chaff, designed to
create radar echoes as a decoy or diversion tactic.
angle jamming A radar jamming technique in
which the return echo is jammed with a signal
containing improper azimuth or elevation angle
angle modulation Variation of the angle of a sine-
wave carrier in response to the modulating
source, as in FREQUENCY MODULATION and
angle noise In radar reception, the interference re-
sulting from variations in the angle at which an
AND gate 1. AND circuit. 2. In a TV receiver, an
echo arrives from the target.
AND circuit that holds the keyed-AGC signal off
angle of arrival The angle which the line of propa-
until a positive horizontal flyback pulse and a
gation of an incoming radio wave makes with the
horizontal sync pulse appear simultaneously at
surface of the earth. Compare ANGLE OF DE-
the input.
android A sophisticated robot built in humanoid
angle of azimuth The horizontal angle between
form. Usually, it propels itself by rolling on
the viewer and object or target, usually measured
wheels or on a track drive. A rotatable head con-
clockwise from north.
tains position sensors, a machine vision system,
angle of beam The angle enclosing most of the
and/or a machine hearing system. Mechanical
transmitted energy in the radiation from a direc-
arms are equipped with end effectors to perform
tional antenna. It is usually measured between
various tasks. The most advanced androids have
the half-power points in the main lobe of the di-
self-contained computer control systems.
rectional pattern. This angle can be measured in
anechoic Pertaining to the absence of echoes. Ex-
the horizontal (azimuth) plane or in the vertical
amples: ANECHOIC CHAMBER, anechoic enclo-
(elevation) plane.
sure, or anechoic room.
30 angle of conduction • anhysteresis

angle of conduction 1. Also called angle of flow. frequency. Compare ANGLE OF LAG. Also see
The number of degrees of an excitation-signal cy- PHASE ANGLE.
cle during which output (drain, collector or plate) angle of radiation 1. The angle, measured with re-
current flows in an amplifier circuit. 2. The num- spect to the horizon, at which the principal lobe of
ber of degrees of any sine wave at which conduc- an electromagnetic wave leaves a transmitting
tion of a device (e.g., a diode) begins. antenna. 2. The angle, measured relative to the
angle of convergence 1. In any graphical repre- horizon, of a receiving or transmitting antenna™s
sentation, the angle formed by any two lines or optimum sensitivity.
plots that come together at a point. 2. The angle angle of reflection The angle, measured relative to
formed by the light paths of two photocells fo- the perpendicular (orthogonal) to a surface, sub-
cused on the same object. tended by a ray leaving the surface after having
angle of declination The angle between the hori- been reflected from it. Compare ANGLE OF INCI-
zon and a descending line. Compare ANGLE OF DENCE.
ELEVATION. angle of refraction The angle, measured relative
angle of deflection In a cathode-ray tube, the an- to the perpendicular (orthogonal) to a boundary
gle between the electron beam at rest and a new between two different media, subtended by a ray
position resulting from deflection. leaving the boundary after having been refracted
angle of departure The angle, relative to the thereat. Compare ANGLE OF INCIDENCE.
horizon, made by the line of propagation of a angle tracking noise Noise in a servo system that
transmitted radio wave. Compare ANGLE OF results in a tracking error.
ARRIVAL. angstrom (Anders J. Angstrom, 1814 “1874). A
unit of length used to describe certain extremely
short waves and microscopic dimensions; 1
angstrom equals 10“4 microns (10“10 meters).
angular deviation loss The ratio of microphone or
loudspeaker response on the principal axis of re-
sponse to the response at a designated angle from
that axis. Expressed in decibels.
angular difference See PHASE ANGLE.
angular displacement In an ac circuit, the separa-
tion, in degrees, between two waves. See PHASE
angular frequency The frequency of an ac signal,
expressed in radians per second (rad/sec) and ap-
proximately equal to 6.28f, where f is the fre-
quency in Hertz.
angular length Length, as along the horizontal
axis of an ac wave or along the standing-wave
angle of depression See ANGLE OF DECLINA- pattern on an antenna, expressed as the product
TION. of radians and wavelength.
angle of divergence In a cathode-ray tube, the an- angular-mode keys On a calculator or computer,
gle formed by the spreading of an undeflected the DEG, RAD, and GRAD keys for expressing or
electron beam as it extends from the gun to the converting angles in DEGREES, RADIANS, and
screen. GRADS, respectively.
angle of elevation The angle that an ascending angular phase difference For two sinusoidal
line subtends, with respect to the horizon. Com- waves, the phase difference, expressed in degrees
pare ANGLE OF DECLINATION. or radians.
angle of flow See ANGLE OF CONDUCTION. angular rate In navigation, the rate of bearing
angle of incidence The angle, measured relative to change, expressed in degrees or radians.
the perpendicular (orthogonal) to a surface or angular resolution The ability of a radar to distin-
boundary, subtended by an approaching ray. guish between two targets by angular measure-
OF REFRACTION. angus pen recorder An instrument that makes a
angle of lag The phase difference (in degrees or ra- permanent record of the time whenever a channel
dians) whereby one component follows another in is used.
time, both components being of the same fre- anharmonic oscillator An oscillating device in
quency. Compare ANGLE OF LEAD. Also see which the force toward the balance point is not
PHASE ANGLE. linear, with respect to displacement.
angle of lead The phase difference (in degrees or anhysteresis The magnetization of a material by a
radians) whereby one component precedes an- unidirectional field containing an alternating field
other in time, both components being of the same component of gradually decreasing amplitude.
anhysteretic state • anomalous propagation

anhysteretic state The condition of a substance anode efficiency Also called plate efficiency. In a
after it has been subjected to a strong magnetic power amplifier using an electron tube, the ratio
field, the intensity of which alternates in direction Po/Pi, where Po is the output power in watts and Pi
and diminishes gradually to zero. is the dc anode power input in volt-amperes.
animism A belief or philosophy, held especially in anode power input Symbol, PA(input). The product of
Eastern civilizations, such as Japan, that all anode current and anode voltage.
things contain an essence of life. This theory ren- anode power supply The ac or positive dc power
ders irrelevant the question of whether or not ma- supply unit that delivers current and voltage to
chines, such as computers and robots can be the anode of a device.
“alive.” anode saturation The point beyond which a fur-
anion A negative ion. Also see ION. ther increase in anode voltage does not produce
anisotropic Pertaining to the tendency of some an increase in anode current.
materials to display different magnetic and other
physical properties along different axes.
anneal To heat a metal to a predetermined temper-
ature and let it cool slowly. The operation pre-
vents brittleness and often stabilizes electrical
annealed laminations Core laminations for trans-
formers or choke coils that have been annealed.
annealed shield A magnetic shield for cathode-ray
tubes, that has been processed by annealing.
annealed wire Soft-drawn wire that has been sub-
jected to annealing.
annotations 1. Marking on copies of original engi-
neering-installation documents to show changes
made during the installation. 2. Any set of com-
ments or notes accompanying a program, an
equipment or system, or a process.
annular 1. Pertaining to the region between two
concentric circles that lie in the same plane; ring-
shaped. 2. Pertaining to two or more concentric
circles that lie in a common plane.
annular conductor A number of wires stranded in
three concentric layers of alternating twists
around a hemp core.
annular transistor A mesa transistor in which the
base and collector take the form of concentric anode strap In a multicavity magnetron, a metal
rings around a central emitter. strap connecting the anodes.
annulling network A subcircuit that shunts a fil- anode terminal 1. In a diode, the terminal to
ter to cancel reactive impedance at the extreme which a positive dc voltage must be applied for
ends of the pass band of the filter. forward bias. Compare CATHODE TERMINAL. 2.
annunciation relay A relay that indicates whether In a diode, the terminal at which a negative dc
or not a circuit is carrying current. voltage appears when the device is used as an ac
annunciator A device that produces loud sound rectifier. Compare CATHODE TERMINAL. 3. The
and/or conspicuous light to attract attention terminal that is connected internally to the an-
(e.g., the electronic siren in an automotive secu- odic element of any device.
rity system). anode voltage Symbol, EA or VA. The difference in po-
anode 1. The positive electrode of a vacuum tube tential between the anode and cathode of a device.
or solid-state device (i.e., the electrode toward anodic Pertaining to the anode of a device, or to
which electrons move during current flow). 2. In anode-like effects.
an electrochemical cell, the electrode that loses anodizing An electrolytic process in which a pro-
electrons by oxidation. This is usually the nega- tective oxide film is deposited on the surface of a
tive electrode. metallic body acting temporarily as the anode of
anode balancing coil Mutually coupled windings the electrolytic cell.
used to maintain equal currents in parallel an- anomalous dispersion Dispersion of electromag-
odes operating from a common transformer ter- netic radiation that is characterized by a decrease
minal. in refractive index with increase in frequency.
anode current Current flowing in the anode circuit anomalous propagation 1. The low-attenuation
of a device. propagation of UHF or microwave signals through
32 anomalous propagation • antenna current

atmospheric layers. 2. Unusual, bizarre, or unex- antenna amplifier 1. A radio-frequency amplifier,
plainable electromagnetic-wave propagation (e.g., often installed at the antenna, used to boost sig-
apparent F-layer ionospheric effects in the FM nals before they reach a receiver (also called an
broadcast band). 3. Rapid fluctuation of a sonar RF preamplifier). 2. Occasionally, the first RF am-
echo because of variations in propagation. plifier stage of a receiver, also known as the front
anoxemia toximeter An electronic instrument for end.
measuring or alerting against the onset of anox- antenna array See ARRAY.
emia (deficiency of oxygen in the blood)”espe- antenna bandwidth The frequency range through-
cially in airplane pilots. out which an antenna will operate at a specified
AN radio range A navigational facility entailing four efficiency without needing alteration or adjust-
zones of equal signal strength. When the aircraft ment.
deviates from course, an aural Morse-code signal, antenna beamwidth A measure of the extent to
A (DIT DAH) or N (DAH DIT) is heard; but when the which a directional antenna focuses a transmit-
aircraft is on course, a continuous tone is heard. ted electromagnetic field, or focuses its response
ANSI Acronym for American National Standards In- to incoming electromagnetic fields. Expressed as
stitute. the angle in degrees between opposite half-power
AN signal The signal provided by an AN radio range points in the main lobe of the directional pattern.
to apprise aircraft pilots of course deviation. Usually determined in the horizontal plane, but
answerback The automatic response of a terminal occasionally in the vertical plane.
station to a remote-control signal. antenna coil The primary coil of the input RF
answer cord In a telephone system, the cord used transformer of a receiver, or the secondary coil of
for answering subscribers™ calls and incoming the output RF transformer of a transmitter.
trunk calls.
answering machine A device that automatically
answers a telephone and records an audio mes-
sage from the caller.
answer lamp A telephone switchboard lamp that
lights when an answer cord is plugged into a line
jack; it switches off when the telephone answers
and lights when the call is completed.
ant Abbreviation of ANTENNA.
antenna In a communications system, a special-
ized transducer that converts incoming electro-
magnetic fields into alternating electric currents
having the same frequencies (receiving antenna),
or converts an alternating current at a specific
frequency into an outgoing electromagnetic field
at the same frequency (transmitting antenna). An antenna coincidence The condition in which two
antenna can be a simple wire or rod, or a compli- directional antennas are pointed directly toward
cated structure. Thousands of geometries and each other.
specifications are possible. The optimum antenna antenna-conducted interference Extraneous sig-
type for a given situation depends on the commu- nals generated in a transmitter or receiver and
nications frequency, the distance to be covered, presented to the antenna, from which they are ra-
and various other factors. diated.
antenna ammeter An RF ammeter, usually of the antenna core A ferrite rod or slab around which a
thermocouple type, employed to measure current coil of wire is wound to act as a self-contained an-
flowing to a transmitting antenna. tenna, usually in a miniature receiver.
antenna coupler A device consisting of an induc-
tor, RF transformer, or a combination of induc-
tor(s) and capacitor(s), used to match the
impedance of an antenna to that of a transmitter
or receiver. Also known as a transmatch or an-
tenna tuner.
antenna coupling Inductive and/or capacitive
coupling used to optimize the transfer of energy
from an antenna to a receiver, or from a trans-
mitter to an antenna.
antenna current 1. Radio-frequency current flow-
ing from a transmitter into an antenna. 2. Radio-
frequency current flowing from a receiving
antenna into a receiver.
antenna detector • antenna pattern

antenna detector A circuit that warns aircraft jects in the vicinity of an antenna which, taken
personnel that they are being observed by radar. together, form the radio-frequency (RF) ground
It picks up the radar pulses and actuates a warn- system against which the antenna operates.
ing light or other device. Some antennas require an extensive ground sys-
antenna diplexer A coupling device that permits tem to function efficiently; others need no ground
several transmitters to share one antenna with- system.
out troublesome interaction. Compare ANTENNA antenna/ground system An arrangement em-
DUPLEXER. bodying both an antenna and a low-resistance
antenna directivity The directional characteris- connection to the earth, as opposed to an an-
tics of a transmitting or receiving antenna, usu- tenna system that involves no connection to
ally expressed qualitatively (e.g., omnidirectional, earth.
bidirectional, or unidirectional). A more precise antenna height 1. The height of an antenna above
expression is ANTENNA BEAMWIDTH. the surface of the earth immediately beneath the
antenna director In a directional antenna, a PAR- driven element(s). 2. The height of an antenna
ASITIC ELEMENT situated in front of the radiator above the effective radio-frequency (RF) ground
and separated from it by an appropriate fraction immediately beneath the driven element(s). 3.
of a wavelength. Its function is to intensify radia- The height of an antenna above average terrain,
tion in the direction of transmission. Compare determined against the mean altitude of a num-
ANTENNA RADIATOR and ANTENNA REFLEC- ber of points on the earth™s surface that lie within
TOR. a certain radius of the antenna structure. Also
antenna duplexer A circuit or device permitting called height above average terrain (HAAT).
one antenna to be shared by two transmitters antenna impedance The complex-number im-
without undesirable interaction. pedance that an antenna presents to a transmis-
antenna effect The tendency of wires or metallic sion line. It can vary over a tremendous range,
bodies to act as antennas (i.e., to radiate or re- and depends on the antenna type, antenna size,
ceive radio waves). antenna height, operating frequency, and various
antenna efficiency The ratio of radio-frequency other factors.
energy supplied to a wireless transmitting an- antenna-induced potential Also called antenna-
tenna, to the energy radiated into space. Electri- induced microvolts. The voltage across the open-
cally, the radiation resistance of the antenna (RR) circuited terminals of an antenna.
appears in series with loss resistance (RL). The ef- antenna lens Also called lens antenna. A radiator
ficiency Eff of the antenna can be determined by designed to focus microwave energy in much the
the following formula: same manner that an optical lens focuses light
rays. Lens antennas are made from dielectric ma-
Eff = RR/(RR + RL)
terials and/or metals.
As a percentage,
antenna loading 1. The insertion of inductance in
Eff % = 100 (RR/(RR + RL) antenna elements to lower the resonant fre-
quency of the system without necessarily making
The efficiency is always less than 1 (100 percent)
the system physically larger or the elements
because, in practice, the loss resistance can
longer. 2. The insertion of capacitance in antenna
never be reduced to zero.
elements to raise the resonant frequency of the
antenna factor A factor (in decibels) added to an
system without necessarily making the system
RF voltmeter reading to find the true open-circuit
physically smaller or the elements shorter.
voltage induced in an antenna.
antenna lobe A well-defined region in the radiation
antenna field The electromagnetic field immedi-
pattern of an antenna in which radiation is most
ately surrounding an antenna.
intense, or in which reception is strongest. Also
antennafier Low-profile antenna/amplifier device,
sometimes used with portable communications
antenna matching The technique of establishing a
systems. Also called an active antenna.
satisfactory relationship between the antenna
antenna front-to-back ratio For a directional an-
impedance and the transmission-line or trans-
tenna, the ratio of field strength in front of the an-
mitter-output impedance, for maximum transfer
tenna (i.e., directly forward in the line of
of power into the antenna. Also, the matching
maximum directivity) to field strength in back of
of antenna impedance to receiver-input im-
the antenna (i.e., 180 degrees from the front), as
pedance, for delivery of maximum energy to the
measured at a fixed distance from the radiator. It
is usually specified in decibels.
antennamitter An antenna/oscillator combina-
antenna gain For a given antenna, the ratio of sig-
tion that serves as a low-power transmitter.
nal strength (received or transmitted) to that ob-
antenna pattern A polar plot of antenna perfor-
tained with a comparison antenna, such as a
mance that shows field strength versus angle of
simple dipole. Generally specified in decibels.
azimuth, with the antenna at the center. It is
antenna ground system The earth, counterpoise,
usually specified in the horizontal plane.
guy wires, radials, and/or various conducting ob-
34 antenna polarization • anthropomorphism

antenna range 1. The frequency band, communi-
cation distance characteristically covered, or
other continuum of values that specify the oper-
ating limits of an antenna. 2. The region immedi-
ately surrounding an antenna in which tests and
measurements usually are made. Sometimes
antenna reflector In a directional antenna, a PAR-
ASITIC ELEMENT situated behind the radiator
and separated from the latter by an appropriate
fraction of a wavelength. Its function is to inten-
sify radiation in the direction of transmission.
antenna relay In a radio station, a low-loss, heavy-
duty relay that enables the antenna to be
switched between transmitter and receiver.
antenna polarization The orientation of electric antenna resistance The resistive component of
lines of flux, with respect to the surface of the ANTENNA IMPEDANCE.
earth, for which an antenna is most efficient. A antenna resonant frequency The frequency, or
vertical antenna radiates and receives vertically narrow band of frequencies, at which an an-
polarized waves. A horizontal antenna radiates tenna™s impedance appears resistive.
and receives horizontally polarized waves broad- antenna stage 1. The first RF amplifier stage of a
side to itself, and vertically polarized waves at receiver. 2. Occasionally, the final RF amplifier of
high elevation angles off its ends. In other direc- a transmitter.
tions, the polarization is slanted at various an- antenna switch In a radio station, a low-loss,
gles. heavy-duty switch that enables the antenna to be
antenna power Symbol, Pant. The RF power devel- connected to transmitter, receiver, or safety
oped in an antenna by a transmitter; Pant equals ground.
I 2R, where I is the antenna current and R is the
antenna resistance at point I is measured.
antenna power gain The ratio of the maximum ef-
fective radiated power (ERP) from a wireless
transmitting antenna to the ERP from a reference
antenna, expressed in decibels (dB). If the ERP
from an antenna under test is PT watts and the
ERP from the reference antenna is PR watts, then
the gain GdB is:
GdB = 10 log10 (PT/PR)
Power gain is always measured in the direction in
which the test antenna performs the best. The
antenna system Collectively, an antenna and all of
reference antenna, usually a dipole, is chosen
the auxiliary electrical and mechanical devices
with a gain assumed to be unity, or 0 dB. Gain
needed for its efficient operation, including cou-
relative to a dipole is expressed in dBd (decibels
plers, tuners, transmission lines, supports, insu-
relative to a dipole). Alternatively, the reference
lators, and rotator.
antenna can be an isotropic radiator, in which
antenna terminals 1. The points at which a trans-
case the gain is expressed in dBi (decibels relative
mission line is attached to an antenna. 2. The sig-
to an isotropic radiator). Gain figures in dBd and
nal input terminals of a receiver. 3. The signal
dBi differ by a constant amount as follows:
output terminals of a transmitter.
GdBi = 2.15 + GdBd antennaverter An antenna and converter com-
bined into a single circuit, intended for connec-
antenna preamplifier A highly sensitive amplifier
tion to the antenna terminals of a receiver to
used to enhance the gain of a receiver. It is usu-
allow operation on frequencies outside the band
ally used at the very high frequencies and above.
for which the receiver has been designed.
antenna radiation The propagation of radio waves
antenna wire 1. The radiator element of a wire-
by a transmitting antenna.
type antenna. 2. A strong solid or stranded wire
antenna radiator The element of an antenna that
(e.g., hard-drawn copper, copper-clad steel, or
receives RF energy from the transmitter and radi-
phosphor-bronze) used for antennas.
ates waves into space. Also known as the driven
anthropomorphism The perception, by people, of
element. Compare ANTENNA DIRECTOR and AN-
machines as having human qualities. This can
anthropomorphism • antiparticle

example, log 10,000 = log 104 = 4, and thus an-
lead to emotional attachment to hardware, such
tilog 4 = 104 = 10,000.
as computers and robots. The more sophisticated
the apparatus, in general, the more powerful this antilogous pole In a PYROELECTRIC MATERIAL,
perception can become. the end that becomes negatively charged as the
antialiasing filter A low-pass or bandpass filter temperature rises.
that limits the bandwidth of an input signal to antimagnetic Pertaining to materials having ex-
prevent aliasing and its effects. See ALIASING, 1. tremely low RETENTIVITY.
anticapacitance switch A switch whose members antimatter Pertaining to particles that are the
are thin blades and stiff wires widely separated to counterparts of conventional particles (i.e.,
minimize capacitance between them. positrons instead of electrons, antineutrons in-
anticathode The target electrode of an X-ray tube. stead of neutrons, and antiprotons instead of
Anticipatory Sciences A group of futurists, people protons). When a particle meets its antiparticle,
who attempt to predict the course of technology. the two annihilate, releasing energy. Also see AN-
Some futurists believe that progress will continue TIPARTICLE.
until, for example, homes become fully automated antimicrophonic See NONMICROPHONIC.
and artificial intelligence reaches a level compara- antimony Symbol, Sb. A metalloidal element.
ble to human intelligence. Other futurists believe Atomic number, 51. Atomic weight, 121.76. Often
that such things are highly improbable. used as n-type dopant in semiconductor manu-
anticlutter circuit A supplementary circuit in a facture.
radar receiver that minimizes the effect of extra- antineutrino The antiparticle of the NEUTRINO,
neous reflections that would obscure the image of emitted as a result of radioactive decay.
the target. antineutron An uncharged particle with a mass
anticlutter gain control In a radar receiver, a cir- equal to that of the neutron, but with a magnetic
cuit that automatically raises the gain of the re- moment in the direction opposite that of the neu-
ceiver slowly to maximum after each transmitter tron.
pulse to reduce the effect of clutter-producing antinode A point of maximum amplitude in a
echoes. standing wave.
anticoincidence Noncoincidental occurrence of
two or more signals. Compare COINCIDENCE.
anticoincidence circuit In computers and control
systems, a circuit that delivers an output signal
only when two or more input signals are not re-
ceived simultaneously. Compare COINCIDENCE
anticoincidence operation An exclusive-OR oper-
anticollision radar A vehicular radar system that
is used to minimize the probability of a collision
with another vehicle, whether or not that other
vehicle has a similar system. antinoise carrier-operated circuit A circuit that
antiferroelectric 1. Pertaining to the property cuts off the audio output of a receiver while the
wherein the polarization curve of certain crys- station transmitter is in use. This can be accom-
talline materials shows two regions of symmetry. plished in the automatic-gain-control (AGC) cir-
2. A material that exhibits the aforementioned cuit of the receiver, or in the speaker or audio
property. line. The circuit is actuated by energy from the
antiferromagnetic Pertaining to the behavior of transmitted signal.
materials in which, at low temperatures, the antinoise microphone Any microphone that dis-
magnetic moments of adjacent atoms point in op- criminates against acoustic noise (e.g., a lip mi-
posite directions. crophone or throat microphone).
antihunt The condition in which hunting is coun- antinucleon A particle with the mass of a nucleon,
teracted, usually by removing overcorrection in but with the opposite electrical charge and direc-
automatic control or compensation systems. tion of magnetic moment. Compare NUCLEON.
antihunt circuit 1. A circuit that minimizes or antioxidant A material, such as a lacquer coat or
eliminates hunting. Also see ANTIHUNT. 2. In a an inactive oxide layer, that prevents or slows ox-
television (TV) receiver, a circuit that stabilizes an idation of a material exposed to air.
automatic frequency control (afc) system. antiparticle A subatomic particle opposite in char-
antijamming Pertaining to communications sys- acter to conventional particles, such as electrons,
tems that are resistant to, or that counteract, the neutrons, protons. Antiparticles constitute
effects of jamming. antimatter. Also see ANTINEUTRINO, ANTI-
antilogarithm Abbreviated, antilog or log“1. The NEUTRON, ANTINUCLEON, ANTIPROTON, and
number corresponding to a given logarithm. For POSITRON.
36 antiphase • A plus

antiphase The property of being in phase opposi- aperture 1. The larger, normally open end of a
tion (180 degrees out of phase). horn antenna or horn loudspeaker. 2. An opening
antipincushioning magnets In some television in an opaque disk or mask that passes a prede-
(TV) receivers, a pair of corrective magnets in the termined amount of light or other radiant energy.
deflection assembly on the picture tube that elim- 3. The portion of a directional antenna through
inate pincushion distortion (disfigurement of the which most of the radiated energy passes.
raster so that it resembles a pincushion”a rect- aperture angle For an antenna or telescope or mi-
angle with its sides bowed in). croscope, the half angle formed by the radius of
antiproton A subatomic particle with a mass equal the detecting instrument, as viewed from the
to that of the proton, but with opposite electrical source.
antiquark An ANTIPARTICLE of a QUARK.
antirad substance A material that protects against
damage caused by atomic radiation.
antiresonance 1. Parallel resonance. 2. The con-
dition of being detuned from a resonant fre-
antiresonant circuit See PARALLEL-RESONANT

antiresonant frequency 1. The resonant fre-

quency of a parallel-resonant circuit. 2. In a
piezoelectric crystal, the frequency at which
impedance is maximum (as in a parallel-resonant aperture antenna An antenna whose beamwidth
circuit). depends on the size of a horn, reflector, or lens.
antisidetone Pertaining to the elimination in tele- aperture compensation In a television (TV) cam-
phone circuits of interference between the micro- era, the minimizing of APERTURE DISTORTION
phone and earphone of the same telephone. by widening the video-amplifier passband.
antistickoff voltage The low voltage applied to the aperture distortion In a television (TV) camera
coarse synchro control transformer rotor winding tube, a form of distortion that occurs when the

in a dual-speed servo system to eliminate am- scanning beam covers several mosaic elements
biguous behavior in the system. simultaneously. This condition, caused by exces-
antitransmit/receive switch Abbreviated ATR. In sive beam thickness, results in poor image reso-
a radar installation, an automatic device to pre- lution.
vent interaction between transmitter and re- aperture mask In a three-gun color picture tube, a
ceiver. thin, perforated sheet mounted behind the view-
antivirus program A computer program or utility ing screen to ensure that a particular color phos-
designed to detect and eliminate viruses and Tro- phor will be excited only by the beam for that
jan horses in a computer system. color. Also called shadow mask.
antivoice-operated transmission Radio commu- aperture synthesis In telescopes, a method of ob-
nications that use a voice-activated circuit as a taining high resolution using several small anten-
transmitter interlock during reception on the nas separated by great distances. The small
companion receiver. antennas are moved around to simulate the re-
apc 1. Abbreviation of automatic picture control. 2. solving power of a much larger antenna that
Abbreviation of AUTOMATIC PHASE CONTROL. would, in practice, be impossible or impractical to
aperiodic Characterized by a lack of predictable construct.
repetitive behavior. For example, the sferics or aphelion 1. The point at which a solar-orbiting
“static” electromagnetic interference caused by satellite attains its highest altitude. It occurs
lightning. once for every complete orbit. At this point, the
aperiodic current The unidirectional current that satellite travels slower than at any other point in
follows an electromagnetic disturbance in an LCR the orbit. 2. The altitude, measured from the
circuit, in which R is equal to or higher than the sun™s surface or the sun™s center, of a solar-
critical circuit resistance. orbiting satellite at its most distant point.
aperiodic damping Damping of such a high degree APL Abbreviation for A Programming Language. A
that the damped system, after disturbance, high-level computer language designed for ease of
comes to rest without oscillation or hunting. use, and characterized by the requirement for a
aperiodic discharge A discharge in which current special character set.
flowing in an LCR circuit is unidirectional, rather apl 1. Abbreviation of average picture level. 2. Ab-
than oscillatory. For this condition, 1/LC is less breviation of automatic phase lock.
than or equal to R2/4L2. A plus Also, A+. The positive terminal of an A bat-
aperiodic function A nonrepetitive function (e.g., tery. Also, pertaining to the part of a circuit con-
a hyperbolic trigonometric function). nected to that terminal.

apogee • arc cosecant

apogee 1. The point at which an earth-orbiting appliance Electrical equipment in general. This
satellite attains its highest altitude. It occurs might include any home-operated device.
once for every complete orbit. At this point, the application A task or job for which an electronic
satellite travels slower than at any other point in device or system is used. It especially pertains to
the orbit. 2. The altitude, measured from the personal-computer software that has practical


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