. 18
( 42)


opening between the opposite poles of a tape gas cleanup Loss of pressure in a gas-filled tube,
recorder or playback head. eventually leading to failure. Caused by gas ions
gap arrester A lightning arrester consisting of a forming compounds with metal parts or with the
number of metal cylinders separated by air gaps. glass envelope.
gap coding A system in which silent periods are in- gas detector A device for sensing presence of vari-
serted, according to a specific timing code, into a ous gases in the air”especially toxic or explosive
transmission. gases (such as chlorine, hydrogen, or methane).
gap depth In a magnetic recording head, the depth gaseous conduction The conduction of an electric
of the gap (taken perpendicular to the face). Com- current through an ionized gas.
pare GAP WIDTH. gaseous phototube A PHOTOTUBE containing a
gap digit A digit that contributes no intelligence to small amount of a gas suitable for ionic conduc-
the word in which it appears (e.g., a parity bit). tion.
gap energy The energy represented by the forbid- gaseous voltage regulator A gas-filled diode
den gap in electron energy levels (e.g., between across which the voltage drop is substantially
310 gaseous voltage regulator • gated amplifier

constant during the gas discharge and which ac- presence of a gas in the environment and acti-
cordingly delivers a constant output voltage. vates the detector or alarm circuit.
gas-filled cable A sealed cable filled with an inert gassing 1. The generation of gas by a storage bat-
gas that serves as a low-loss dielectric and mois- tery, especially while it is being charged. 2. The
ture barrier. generation of gas during electrolysis.
gas-filled counter tube A radiation counter tube gas sniffer See GAS DETECTOR.
containing a gas that ionizes when irradiated. See gaston A device intended for the purpose of modu-
GEIGER-MUELLER TUBE. lating an aircraft signal, making the signal diffi-
gas-filled lamp 1. An incandescent lamp filled cult to jam. The signal is randomly modulated by
with a gas, such as nitrogen, for improved perfor- noise from the device.
mance. 2. Discharge lamp. gas tube See GAS-FILLED TUBE.
gas-filled tube An enclosure filled with gas that is gas-tube lightning arrester A lightning arrester,
subjected to an electric potential, intended to consisting of a special gas diode. The tube has vir-
produce specific effects, such as light emission or tually infinite resistance at low voltages, but pro-
voltage regulation. vides a low-resistance path to ground when the
gas-flow alarm An electronic circuit that actuates high voltage of a lightning stroke ionizes the gas.
an alarm when the flow of gas through a pipe gas-tube oscillator A relaxation oscillator using a
changes from a predetermined rate. two-element gas tube, such as a neon lamp, as
gas-flow control A servo system for automatically the breakdown device.
maintaining or adjusting the flow of gas through
gas-flow gauge See GAS-FLOW METER.
gas-flow indicator See GAS-FLOW METER.
gas-flow meter An instrument that indicates the
rate of gas flow through a pipe, in terms of volume
per unit time (e.g., cubic feet per minute).
gas-flow switch In a gas-circulating system, a output
switch that actuates an alarm when the gas flow
rate changes.
gas focusing In a cathode-ray tube, a technique by
which a gas is used for the purpose of focusing an gas-tube oscillator
electron beam. The ionization of the gas causes
the electron beam to be made more narrow.
GASH Acronym for guanidine aluminum sulfate gas valve See ELECTROMECHANICAL VALVE.
hexahydrate, an organic crystalline material used gas X-ray tube An X-ray tube in which the positive
as the dielectric in certain ferroelectric capacitors ions of a gas bombard the cathode, which emits
and ferroelectric memory elements. electrons.
gas laser A LASER that uses a gas or mixture of gate 1. A device or circuit that has no output until
gases (instead of a solid rod) as the stimulated it is triggered into operation by one or more en-
medium. Some of the gases used are argon, car- abling signals, or until an input signal exceeds a
bon dioxide, helium, krypton, and neon. predetermined threshold amplitude. 2. The input
gas maser A MASER in which the stimulated ma- (control) electrode of a field-effect transistor or
terial is a gas, such as ammonia. thyristor device (e.g., silicon-controlled rectifier).
gas multiplication See GAS AMPLIFICATION. 3. A signal that triggers the passage of other sig-
gas noise Electrical noise resulting from the undi- nals through a circuit.
rected motion of gas molecules in a gas-filled tube. gate array Basic gates arranged in a pattern on a
gas-pressure alarm An electronic circuit that actu- chip; the gates can be interconnected during
ates an alarm when gas pressure rises or falls. manufacture to form a unit that performs what-
gas-pressure control A servo system for automati- ever function is needed.
cally maintaining or adjusting gas pressure in gate circuit 1. An electronic switching circuit (see
pipes or other channels. GATE, 1). 2. The circuit associated with the gate
gas-pressure gauge See GAS-PRESSURE METER. electrode of a field-effect transistor.
gas-pressure indicator See GAS-PRESSURE ME- gate-controlled switch A device similar to a silicon-
TER. controlled rectifier or thyristor. A negative current,
gas-pressure meter An instrument that indicates applied to the gate, switches the device off.
gas pressure in a pipe or container, but provides no gate current Symbol, IG. Current flowing in the
means for automatically correcting the pressure. gate (control) circuit of a semiconductor device.
gas ratio For a gas-filled tube, the ratio Ii/Ei, where Ii The current is finite in thyristors, but is almost
is the ion current and Ei is the ionization potential. zero in some types of field-effect transistors.
gas sensor Any element, such as the filament in a gated amplifier An amplifier whose input is effec-
hot-filament gas detector, that responds to the tively switched on and off by gating signals.
gated buffer • Gauss™ theorem

gated buffer A low-voltage, high-current driver, gate terminal 1. The terminal connected to the
used for differentiation in a multivibrator circuit. gate semiconductor in a field-effect transistor.
gated flip-flop A flip-flop in which it is impossible 2. The terminal, or terminals, connected to the
for both outputs to be low simultaneously. input or inputs of a digital-logic network.
gate-dip meter A dip meter using a field-effect- gate trigger current In a gate-controlled semicon-
transistor oscillator with the indicating microam- ductor switch, the current flowing in the gate cir-
meter in the gate circuit. cuit when the device is being switched on by a
gate-dip oscillator See GATE-DIP METER. gate trigger voltage.
gated multivibrator A rectangular-wave generator gate trigger voltage In a gate-controlled semicon-
that produces a gate voltage when triggered. ductor switch, the trigger voltage required to ac-
gate-drain voltage Symbol, VGD. In a field-effect tuate the device.
transistor, the maximum voltage permitted be- gate turn-off current In a gate-controlled semicon-
tween the gate and drain electrodes. ductor switch, the low value of gate current that
gated sweep 1. In radar, a sweep whose initiation flows when the device is being switched off. Turn-
and duration are closely controlled to eliminate off current varies with collector (anode) current.
echoes in the image. 2. A circuit providing the ac- gate turn-off voltage In a gate-controlled semi-
tion described in 1. conductor switch, the low value of gate voltage
gate electrode See GATE, 2. that causes the device to switch off.
gate impedance 1. The impedance of the gate elec- gate voltage 1. The voltage applied to the gate
trode of a field-effect transistor with respect to the electrode of a field-effect transistor. See GATE-
other electrode, which serves as the return. 2. SOURCE VOLTAGE. 2. The instantaneous gate-
The impedance of the gate winding of a magnetic cathode voltage in a silicon-controlled rectifier. 3.
amplifier. The voltage across the gate winding of a magnetic
gate leakage current See GATE REVERSE CUR- amplifier.
RENT. gate winding In a magnetic amplifier, a winding
gate nontrigger voltage Symbol, VGnt. For a thyris- that produces gating action.
tor, the direct-current (dc) voltage applied be- gating 1. The process of using one signal to switch
tween the gate and the cathode, above which the another (or part of another) on or off for a desired
device fails to maintain its rated blocking voltage. interval. 2. Selecting a part of a wave for observa-
gate power dissipation Symbol, PG. In a silicon tion or for control purposes.
controlled rectifier, the power consumed by the gauge 1. Any device, such as a METER, used for
gate-cathode path. the purpose of measuring the magnitude of a
gate-protected MOSFET A metal-oxide-semicon- quantity. 2. Wire data and measurements (see
ductor field-effect transistor in which the gate WIRE GAUGE, 1, 2, 3). 3. Sheet metal thickness
electrode is protected from accidental burnout via (e.g., 10 gauge).
built-in Zener diodes, connected back-to-back. Gauss (Karl F. Gauss, 1777“1855) Unit of magnetic
gate pulse 1. A pulse applied to the gate electrode flux density, equivalent to one line of flux per
to actuate a gate-controlled semiconductor de- square centimeter. The SI (preferred) unit of mag-
vice. 2. An actuating pulse in a gate circuit. netic flux density is the TESLA (webers per
square meter); 1 gauss equals 10“4 teslas (symbol,
gate recovery time Symbol, tGr. For a silicon-
controlled rectifier, an extension of the reverse T). Also see FLUX DENSITY.
recovery time: the interval following application of Gaussian curve See BELL-SHAPED CURVE.
the reverse voltage required before the forward Gaussian distribution In statistics, the symmetri-
blocking voltage can be reapplied and then cal distribution described by a bell-shaped curve.
blocked by the device. Also called NORMAL DISTRIBUTION.
gate reverse current Symbol, IGSS. In a field-effect Gaussian function A mathematical function used
transistor, reverse current in the gate-source cir- in the design of lowpass filters. The Gaussian re-
cuit. Also called gate leakage current. sponse is characterized by low band-edge selec-
gate signal 1. The input or control signal applied tivity, high transition bandwidth, negligible step
to the gate electrode of a semiconductor device. 2. response overshoot, and low step-response delay
An actuating signal in a gate circuit. time.
gate-source breakdown voltage Symbol, BVGSS. Gaussian noise Electrical noise whose amplitude-
The voltage at which the gate junction of a junc- versus-frequency characteristic is described by
tion field-effect transistor (JFET) enters the GAUSSIAN DISTRIBUTION.
avalanche. Gaussian waveform A waveform that results in min-
gate-source pinchoff voltage Symbol, VP. In a imal side lobes in a pulse-compression system.
field-effect transistor, the gate-source voltage at gaussmeter See FLUXMETER.
which the conduction channel just closes. Gauss™ theorem Across any closed surface within
gate-source voltage Symbol, VGS. In a field-effect an electric field, the total flux is approximately
transistor, the direct-current (dc) voltage between equal to 12.566 times the enclosed quantity of
the gate and source electrodes. electric charge.
312 gauze resistor • general class license

Geiger counter A radioactivity rate-counting in-
strument based on the GEIGER-MUELLER
TUBE. Pulses from the tube drive a transistor,
which, in turn, drives a meter or digital counter to
indicate the count.

Trigger 8 range

M tube
d Detector
i voltage
a supply

Gaussian distribution Geiger counter

gauze resistor See WOVEN RESISTOR. Geiger-Mueller counter See GEIGER COUNTER.
GAVRS Abbreviation of gyrocompass attitude verti- Geiger-Mueller region For a GEIGER-MUELLER
cal reference system. TUBE, the range of voltages within which the out-
GCA Abbreviation of GROUND-CONTROLLED put pulse amplitude is constant, regardless of
APPROACH. ionizing radiation intensity.
GCI Abbreviation of GROUND-CONTROLLED Geiger-Mueller threshold The lowest voltage in
INTERCEPTION. the Geiger-Mueller region.
GCM Abbreviation of gyrocompass module. See Geiger-Mueller tube A gas-filled radiation detec-
GYROCOMPASS. tor/counter tube consisting of a straight wire as
GCT Abbreviation of GREENWICH CIVIL TIME. an anode, surrounded by a cylindrical cathode.
Gd Symbol for GADOLINIUM. The tube is biased by high voltage. Radiation pen-
G display See G SCAN. etrating the tube ionizes the gas; each ionizing
GDO 1. Abbreviation of GRID-DIP OSCILLATOR. event causes an output pulse.
2. Abbreviation of GATE-DIP OSCILLATOR. Geiger point counter See POINT COUNTER.
Ge Symbol for GERMANIUM. Geiger region See GEIGER-MUELLER REGION.
gear 1. Collectively, electronic equipment. 2. A Geiger threshold See GEIGER-MUELLER THRES-
toothed wheel commonly used in mechanical de- HOLD.
vices. Geissler tube A simple gas-filled glow-discharge
gearmotor An electric motor with a gear train for tube with metal electrodes sealed in each end.
speed changing. When a sufficiently high voltage is applied be-
gear-wheel pattern A pattern produced on an os- tween the electrodes, the highly rarefied gas ion-
cilloscope by intensity-modulating a circular izes and glows with the color associated with the
trace. A signal of unknown frequency fx is applied particular gas used.
to the intensity-modulation (z-axis) input. The gel A substance equivalent to colloidal solution in
signal produces corrugations in the trace. If there the solid phase (e.g., silica gel).
are n corrugations around the trace, and if the gel battery A rechargeable electrochemical BAT-
trace itself completes fs revolutions per second, TERY designed for use with portable electronic
then the unknown frequency fx, in Hz, is equal to and computer equipment. Noted for its ability to
nfs. Compare SPOT-WHEEL PATTERN. deliver high current for short periods, when nec-
essary, and also to deliver moderate current con-
tinuously throughout its discharge cycle.
gen Abbreviation of GENERATOR.
genemotor Contraction of generator/motor, a
(usually battery-driven) dynamotor that has sep-
fx = nfs arate motor and generator windings on the same
armature core.
general class license An amateur-radio license
that conveys some privileges in the high-
frequency bands, and all operating privileges in
the very-high-frequency region and above. An ex-
amination of moderate difficulty is required.
gear-wheel pattern
General Packet Radio Service • geometric progression

General Packet Radio Service A form of packet varying capacitance; the ac is proportional to the
radio especially designed for mobile use. Sub- voltage.
scribers pay for the volume of data they send and generation 1. The production of a signal or carrier
receive, rather than for the time they spend ac- wave. 2. The conversion of some non-electrical
cessing the network. This optimizes the efficiency form of energy (usually mechanical) into electrical
of the network, both from an engineering stand- energy. 3. The number of recording steps be-
point and a financial standpoint. See PACKET tween a master recording and a copy. 4. A copy of
COMMUNICATIONS. data in any form (e.g., tape recording, disk file,
general-purpose bridge See UNIVERSAL BRIDGE. and photocopy).
general-purpose component A component de- generation number A number that identifies the
signed or used for a wide range of applications. age of a file; it is included in the file label on the
For example, a general-purpose germanium disk or tape containing the file.
diode is useful as a detector, mixer, limiter, clip- generator 1. Symbol, G. Any signal source. 2. A
per, meter rectifier, automatic-gain-control (AGC) rotating machine for producing electricity. 3. An
rectifier, and curve changer. electronic device for converting direct current into
general-purpose computer A computer that can alternating current of a specific frequency and
be used in a number of applications for which it waveshape. 4. In computer operation, a routine
was not specifically designed. (akin to a compiler) that will produce a program
general-purpose diode A small-signal semicon- to perform a specific version of some general op-
ductor diode that is useful for a variety of ap- eration by implementing skeletal coding, accord-
plications, such as detection, light-duty ing to specific parameters (e.g., sort generator).
rectification, limiting, logic switching, etc. generator efficiency The ratio of consumed power
general-purpose function generator A nonspe- to delivered power in a generator. It is usually ex-
cialized function generator that is capable of gen- pressed as a percentage.
erating a variety of different waveforms. generator noise Electrical noise caused by a rotat-
general-purpose program A program for the solu- ing generator. Also see GENERATED NOISE, 2.
tion of a class of problems or for a specific prob- generator-type microphone A microphone that
lem, according to certain parametric values. Also produces an output voltage without the need for
called general routine. a supply voltage. Examples: ceramic, crystal, dy-
general-purpose relay Any relay that can be used namic, electret, and velocity types.
in various situations, such as for switching alter- generator-type transducer A transducer that con-
nating or direct currents. verts mechanical motion into an electrical signal
general-purpose tester An instrument, such as a of a proportional voltage. In such a transducer, an
voltohm-milliammeter, that offers several test ca- armature or conductor moves in a magnetic field.
pabilities. generic A form of software collection. Several
general-purpose transistor A transistor that can specialized software packages can be derived
be used in several applications, such as audio from the generic collection, for use in different
amplification, detection, and oscillation. systems.
general service code See CONTINENTAL CODE. geodesic 1. On a surface, the shortest path between
generate 1. To produce a signal or carrier wave. two points. 2. The shortest path between two geo-
2. To convert some non-electrical form of energy graphical locations, measured over the surface of
(usually mechanical) into electrical energy. the earth. Also called geodetic and great circle.
3. To develop subroutines from parameters ap- geodesy The branch of applied mathematics con-
plied to skeletal coding. 4. To use a program cerned with the precise dimensions of the earth.
generator to produce a specialized version of a geodetic system The application of a computer to
general-purpose program. seismographic studies for the purpose of reduc-
generated address An address developed by pro- ing drilling and mining costs.
gram instructions for later use by that program. geomagnetic field See EARTH™S MAGNETIC
generated noise 1. Electrical noise caused by bat- FIELD.
tery action (i.e., between dissimilar metals) in a geomagnetism The earth™s magnetism. Also see
component, such as in a potentiometer. 2. Elec- EARTH™S MAGNETIC FIELD.
trical noise caused by small output variations of geometric capacitance The ratio of the free
generating devices (rotating machines, vibrators, charge of a capacitor to the voltage across its
etc.). Also called generator noise. terminals.
generating magnetometer See EARTH INDUC- geometric mean The nth root of the product of n
TOR. quantities.
generating station An electric power station. geometric progression A mathematical sequence
generating voltmeter An instrument based on a in which each term after the first is obtained by
rapidly spinning variable capacitor. A direct- multiplying the preceding one by a constant
current (dc) voltage applied to the capacitor is quantity (e.g., 1, 2, 4, 8, 16, 32, 64, . . .). Also
converted into an alternating current (ac) by the called geometric sequence.
314 geometric symmetry • GIGO

geometric symmetry In a bandpass or band- germanium dioxide Formula, GeO2. A gray or
rejection filter, a condition in which the response white powder obtainable from various sources; it
is identical on either side of the center frequency. is reduced in an atmosphere of hydrogen or he-
Also called mirror-image symmetry. lium to yield germanium, a semiconductor mate-
germanium junction diode A germanium diode
that contains a pn junction.

germanium photocell A photoconductive cell con-
sisting of a reverse-biased germanium point-
contact diode or germanium junction diode.
germanium point contact The contact between a

pointed metal wire and a germanium wafer, as in
a point-contact diode or point-contact transistor.
germanium rectifier A power rectifier that con-
tains a germanium pn junction.

germanium transistor A transistor in which
germanium is the semiconductor material. Such
a transistor has lower internal resistance and
greater temperature drift than a silicon transis-
German silver A copper-nickel-zinc alloy used in
some resistance wires. Also called NICKEL SIL-

GEV Abbreviation of ground effect vehicle.
gfi Abbreviation of GROUND-FAULT INTER-

g-force See GRAVITY, 2.
G/G Abbreviation of GROUND-TO-GROUND.

ghost In television reception, a slightly displaced
image appearing on the screen simultaneously
with its twin (the false member of a double im-
ghost signal Any signal (such as an undesired re-
flection) that produces a ghost.
geometric symmetry
GHz Abbreviation of GIGAHERTZ.
Gibson girl A portable radio transmitter, powered by
george box In an intermediate-frequency amplifier,
an integral crank-operated generator, introduced
a device used to reject jamming signals. Any jam-
during World War II for pilots forced down at sea.
ming signal with an amplitude lower than a cer-
giga- Abbreviation, G. 1. A prefix meaning billion
tain minimum is rejected.
(109). 2. In digital data applications, a prefix
geostationary orbit An orbit in which a satellite
meaning 230.
revolves around the earth exactly once a day, so it
gigabit A unit of digital data, equal to 230 bits or
remains over the same place on the earth all the
1024 megabits. Also see BIT and MEGABIT.
time. The altitude must be 22,300 miles, and the
gigabyte A unit of digital data, equal to 230 bytes or
orbit must lie in the plane of the earth™s equator.
1024 megabytes. Also see BYTE and MEGABYTE.
geostationary satellite A satellite in GEOSTA-
gigacycle See GIGAHERTZ.
TIONARY ORBIT. It is always in the same spot
gigaelectronvolt Abbreviation, GeV. A large unit of
in the sky from any given observing point. A
voltage; 1 GeV equals 109 eV. Also see BEV,
geostationary satellite provides coverage over
about 40 percent of the earth, and is commonly
used for communications and weather-observa-
gigahertz Abbreviation, GHz. A unit of ultra-high
tion purposes.
frequency; 1 GHz equals 1,000,000,000 Hz = 109
germanium Symbol, Ge. A metalloidal element.
Atomic number, 32. Atomic weight, 72.59. Used
gigaohm A unit of extremely high resistance, reac-
in semiconductor diodes, photocells, rectifiers,
tance, or impedance, equal to 1,000,000,000
and transistors.
ohms = 109 ohms.
germanium diode A diode in which the semicon-
GIGO Abbreviation of garbage in = garbage out, an
ductor material is specially processed germa-
expression signifying that incorrect or improper
GIGO • glucinium

input to a computer will produce meaningless Glide-path
output. beam
gilbert (William Gilbert, 1540“1603) A unit of mag-
netomotive force, equal to 1.26 times the number
of ampere-turns. The SI (preferred) unit of mag-
netomotive force is the ampere (symbol, A); 1
gilbert = 0.796 A. Runway
gilbert per centimeter See OERSTED.
gimbal A suspension device whose orientation can
be changed without affecting the attitude of the Transmitter
body being suspended.
gimmick 1. Colloquialism for any unnamed de- glide-path transmitter
vice. Also see GADGET. 2. Colloquialism for any
tricky manipulation or design. 3. A low-value ca-
pacitor made by twisting two short pieces of insu- glide-path transmitter A radio-frequency trans-
lated wire together. mitter that produces a guidance beam for aircraft
gimp Colloquialism for the tinsel and cloth con- landing purposes. The aircraft follows the beam
ductor used in some earphone cords. toward the runway.
Giorgi system The meter-kilogram-second (mks) glide slope See GLIDE PATH.
system of units. G line A microwave conductor consisting of a
GJD Abbreviation of GERMANIUM JUNCTION round wire coated with a dielectric.
DIODE. glitch 1. In a television image, a narrow, horizontal
glass A hard, brittle, amorphous, and usually interference bar that moves vertically. 2. A very
transparent substance that is largely silicon diox- short and unwanted high-amplitude transient
ide. Glass has a multitude of uses in electronics, that recurs irregularly in an electronic system.
and there are several kinds, each having different glitter 1. In radar, an echo or set of echoes that
electrical properties. The dielectric constant fluctuates rapidly in intensity because of motion
ranges from about 4 to 10; the dielectric strength in the target. 2. A system in which moving devices
ranges from about 20 to 300 kilovolts per mil- are used to confuse enemy radar systems.
limeter. gloss factor For a reflecting surface, the ratio of re-
glass arm A stiffness of the wrist or forearm, some- flected light in a selected direction to reflected
what resembling writer™s cramp, sometimes expe- light in all directions.
rienced by radiotelegraph operators or wire glossmeter An instrument for determining GLOSS
telegraph operators after prolonged use of a hand FACTOR.
key. glow discharge The luminous electrical discharge
glass bulb The glass enclosure of electron tubes resulting from the passage of current through
and incandescent lamps. ionized gas in a partially evacuated tube. The
glass capacitor A capacitor that uses thin glass as color of the glow is characteristic of the particular
the dielectric, and usually has plates consisting gas used.
of metal electroplated or electrodeposited on op- glow-discharge microphone A device that pro-
posite faces of the glass. Also see MOLDED duces audio-frequency currents from the action
GLASS CAPACITOR. of sound waves in a glow-discharge tube.
glass diode A semiconductor diode molded in glass. glow-discharge tube A partially evacuated tube
glass electrode A probe used with a pH meter; it that contains two or more electrodes. The rarefied
consists of a thin-walled glass tube containing gas in the tube glows when a sufficient voltage is
potassium chloride and mercurous chloride. Also applied to the electrodes. See DISCHARGE LAMP,
glass envelope See GLASS BULB. glow lamp See DISCHARGE LAMP.
glassivation A procedure for encapsulating semi- glow modulator tube A gas tube whose luminous
conductor devices in glass or other dielectric ma- output can be modulated by an audio input signal.
terial. glow potential The voltage at which glow dis-
glass-metal seal See GLASS-TO-METAL SEAL. charge just begins in a gas-filled tube.
glass plate capacitor See GLASS CAPACITOR. glow switch In fluorescent light circuits, an elec-
glass shell See GLASS BULB. tron tube containing two bimetal strips that make
glass-to-metal seal A bond between glass and mutual contact when heated by the glow dis-
metal in electronic devices, such as vacuum tubes, charge.
feedthrough terminals, and glass capacitors. glow tube See DISCHARGE LAMP, FLUORES-
glass tube A vacuum tube whose elements are CENT TUBE, GLOW MODULATOR TUBE, NEON
housed in an evacuated glass envelope. BULB, and STROBOTRON.
glide path The guidance beam used by aircraft glow voltage See BREAKDOWN VOLTAGE, 2.
making instrument landings. glucinium See BERYLLIUM.
316 gluon • Graffiti

gluon A subatomic particle that is believed to bind governor 1. A device that prevents a motor or en-
quarks together (coined by Prof. Murray Gell- gine from running faster than a certain speed.
Mann of California Institute of Technology). 2. Any device that limits a circuit parameter.
GM Abbreviation of Geiger-Mueller (see, for exam- g parameters Conductance parameters obtained
ple, GEIGER-MUELLER TUBE). for the equivalent-pi model of a transistor: gBE,
gm Abbreviation of gram. Also abbreviated g. gGC, gCE, and gm.
g-m Abbreviation of GRAM-METER. GPI Abbreviation of GROUND-POSITION INDICA-
gm-cal Abbreviation of GRAM-CALORIE. TOR.
gm-cm Abbreviation of GRAM-CENTIMETER. GPRS Abbreviation for GENERAL PACKET RADIO
GMT Abbreviation of GREENWICH MEAN TIME. gr Abbreviation of grain(s).
G/M tube See GEIGER-MUELLER TUBE. graceful degradation A computer programming
gnd Abbreviation of GROUND. technique used to prevent debilitating breakdown
go Symbol for OUTPUT CONDUCTANCE. by operating the system”even though several
gold Symbol, Au. A precious metallic element. subsystems have malfunctioned; also known as
Atomic number, 79. Atomic weight, 196.967. crippled mode.
Electrical contacts that must have low radio- grad A unit of angular measurement equal to 0.9

frequency resistance, and that must be degree.
relatively immune to corrosion, are often plated graded-base transistor See DIFFUSED-BASE

with gold. TRANSISTOR.
gold-bonded diode A germanium point-contact graded filter A power-supply filter that supplies
diode having a fine gold wire whose point is direct-current output at various points in the fil-
bonded to the germanium wafer. Its principal fea- ter sequence. Thus, the points in the powered
tures are high forward current and almost con- equipment that can tolerate the least ripple are
stant, low reverse current. connected to the filter output, and those that can
gold doping The diffusion of gold into the base and tolerate appreciable ripple are connected to the
collector regions of a diffused-mesa transistor; it filter input; fairly critical points are connected to
shortens carrier storage time. an intermediate position in the filter, such as at

golden ratio A set of proportions used in the de- the junction of two chokes.
sign of some speaker cabinets. The width (W) is 5„8
of the height (H); the depth (D) is 5„8 of the width. ’ ’
These correspond to a ratio H : W : D = 1.000 :
Out Out
0.625 : 0.391. These proportions are thought by
some acoustics engineers to result in the best + +
possible sound quality.
gold-leaf electroscope See ELECTROSCOPE.
Goldschmidt alternator An early dynamo for gen-
erating radio-frequency power. The high- C
frequency energy was not generated directly by ’ ’
the machine, but by resonant circuits and
frequency-multiplying interaction between
graded filter
Golf Standard phonetic alphabet code word for the
letter G.
goniometer 1. Generically, any radio direction graded-junction transistor A grown-junction
finder. 2. An inductive coupler having a sec- transistor in which the temperature of the melt
ondary coil rotated by a dial calibrated to read az- and the rate at which the crystal is pulled from it
imuth. The coupler, when used with a suitable are closely controlled as the n and p layers are
antenna system, comprises a direction finder. formed.
3. A device for electrically varying the directional gradient The rate at which a variable quantity in-
pattern of an antenna. creases or decreases. See, for example, VOLTAGE
go-no test A test that indicates only acceptance or GRADIENT.
rejection of a device. No diagnosis is made. gradient microphone A microphone whose output
GOTO In computers and programmable calcula- varies with sound pressure. Also see PRESSURE
tors, an instruction that, followed by a suitable MICROPHONE.
label, directs the program to that label. Graetz bridge A full bridge rectifier (i.e., one hav-
goto circuit In a digital-logic circuit, a device that ing a diode in each arm).
senses the direction of electric current. Graffiti 1. Trade name for a specialized written al-
goto pair A pair of diodes connected in reverse se- phabet used for entering data into a handheld
ries used in digital-logic circuits. computer using a stylus. 2. The entry of data into

Graffiti • graphic panel

a handheld computer using a stylus. See HAND- graph 1. A presentation of data, particularly a de-
HELD COMPUTER. piction of the manner in which one variable or set
grain boundary In a polycrystalline solid, a bound- of variables changes, with respect to another.
ary between single crystalline regions. Can be in the form of discrete points, curves,
gram 1. Abbreviation, g. A unit of mass and bars, columns, pie-shaped slices, etc. 2. A curve
weight, equal to 0.001 kilogram or 0.0353 ounce. or set of curves in a coordinate system.
2. A suffix meaning something drawn (written), or graphical analysis The solution of problems
recorded, as in radiogram or electrocardiogram. through the use of graphic devices, such as vec-
gram atom See GRAM ATOMIC WEIGHT. tor diagrams, load lines, Nyquist plots, topologi-
gram atomic weight Also called gram-equivalent. cal flow diagrams, etc.
The quantity of an element with a mass in grams graphical harmonic analysis See SCHEDULE
that is equal to the atomic weight of the element. METHOD.
For example, copper has an atomic weight of graphical user interface Acronym, GUI (pro-
63.546; therefore, one gram atomic weight of cop- nounced “gooey”). An operating system or soft-
per has a mass of 63.546 grams. ware that makes it easy for lay people to use a
gram-calorie Abbreviation, gm-cal. The amount of computer. Commands are given by making
heat required to raise the temperature of one choices from among items displayed on the
gram of water by one degree Celsius. screen. Popular versions use symbols, called
gram-centimeter Abbreviation, gm-cm. The work icons, along with a pointing device, such as a
done by a force of one gram exerted over a dis- mouse or trackball.
tance of one centimeter. Also see JOULE. graphic documentation Records of data in the
gram-equivalent See GRAM ATOMIC WEIGHT. form of graphs, charts, tables, diagrams, etc.
grammar 1. The sequence of words and/or abbre- graphic equalizer A device for tailoring the ampli-
viations in a communication or part of a commu- tude-versus-frequency response of a high-fidelity
nication. 2. The sequence of codes and/or audio system. Consists of a splitter, several audio
commands in a high-level computer program- filters, and a mixer. The gain of each filter is ad-
ming language. justable via a slide potentiometer. The poten-
gramme armature See GRAMME RING. tiometers are arranged on the front panel in such
Gramme ring A type of armature for a motor or a way that their relative positions show the ap-
generator, consisting of an iron ring onto which is proximate shape of the response curve.
wound a coil of wire, each turn being connected
to a commutator bar.
gram-meter Abbreviation, g-m. A unit of work
30-Hz filter
equal to a force of one gram exerted over a dis-
tance of one meter. Compare JOULE.
gram-molecular weight See MOL. 100-Hz filter
gram molecule See MOL.
gramophone Archaic term for phonograph.
300-Hz filter
grandfather cycle A backup scheme in a magnetic
reproduction system. The original records are re-
tained for a period of time so that new copies of 900-Hz filter
high precision can be made in case of loss.
grandfather file An original copy of a file on a mag-
2.5-kHz filter
netic disk or tape, retained as a source for recon-
struction as needed. Usually, three generations of
a file (grandfather, father, and son) are kept, each
7-kHz filter
identified by a generation number. Sometimes Input
the terms grandparent, parent, and child are used
18-kHz filter
grand synthesizer A hypothetical child with a
mind perfectly attuned to artificial intelligence
graphic equalizer
(AI), who grows up to revolutionize the whole in-
dustry; a “grand master of AI.”
granular carbon Carbon in the form of fine gran- graphic instrument See GRAPHIC RECORDER.
ules, used in the button of a carbon microphone. graphic-level recorder An instrument that makes
granularity 1. In a digital device, the smallest in- a permanent recording of signal amplitude as a
crement that can be differentiated. 2. The limit of function of some independent variable (such as
detail in a reproduction system. time, frequency, or direction).
granule One of many narrow frequency subbands, graphic panel In process control, a panel of illumi-
the combination of which composes a complete nated lights or dials that display the status of a
signal. Each subband carries its own specific data. process.
318 graphic recorder • gray tin

graphic recorder An instrument in which a signal- by the earth™s drawing of bodies toward its center,
driven pen or stylus makes a permanent record of causing them to have weight. 2. Abbreviation, g.
a quantity on graph paper. The paper passes at a The rate at which a free-falling mass accelerates
controlled speed beneath the pen. in a vacuum at the earth™s surface; equal to 9.802
meters per second per second (m/s2). 3. The rate
graphics 1. Diagrams, charts, photos, tables, or
similar, often symbolic, artwork used to convey at which a free-falling mass accelerates in a vac-
information. 2. The video display in a computer uum in the vicinity, or at the surface, of an astro-
system. 3. Computer software designed specifi- nomical object, such as a planet or star.
cally to create and edit illustrations. gravity cell An electrochemical cell in which the
graphic solution 1. A method of depicting the so- positive electrode is made of copper and the neg-
lution(s) to a problem or equation by means of ative electrode is made of zinc. The copper elec-
graphs. 2. The process of solving problems or trode is placed at the bottom of a jar, and the zinc
equations with the aid of graphs. electrode is placed at the top. The jar is half filled
graphic terminal A display or plotter that provides with copper sulfate solution, and then filled with
visual output of a computer run. zinc sulfate solution. The solutions remain sepa-
graphite A soft form of carbon used in resistors, rate because copper sulfate has a higher specific
attenuators, contacts, brushes, vacuum-tube gravity than zinc sulfate.
plates, cathode-ray tube coatings, etc. gravity wave A disturbance in a gravitational field,
graphite-line resistor An emergency, makeshift such as might be caused by a collapsing star.
resistor consisting of a pencil line drawn on a These waves might emanate from black holes or
piece of paper. The heavier the line for a given rapidly spinning neutron stars.
width and length, the lower its resistance. gray body A radiating body exhibiting constant
graphophone Archaic term for phonograph. spectral emissivity at all wavelengths. That is, the
grasping planning A scheme that a robot arm and emitted energy is the same at all wavelengths and
gripper use to get hold of a particular object. It all frequencies.
can use a vision system, a bar-code reader, tactile Gray code A computer code in which the expres-
sensing, and/or proximity sensing. The robot sions representing sequential numbers differ in
controller (computer) must be programmed to only one bit.
recognize the input from these devices, and to gray scale A reference scale for use in black-and-
seek out the object. white television and video display images, con-
grass The background noise (noise floor) on the sisting of several defined levels of brightness with
display of a spectrum analyzer; it also appears on neutral color.
certain types of radar displays.
grasshopper fuse A special type of spring-operated Gray scale:
fuse. When it burns out, it actuates an alarm that hypothetical 16-shade binary codes.
alerts personnel of a possible circuit or system
Code Relative shade brightness
graticule Calibrated gridwork, as on the face of an
oscilloscope or spectrum-analyzer screen. 0000 Black 0.00
grating A set of parallel, closely spaced, equidis- 0001 6.67
tant conductors or bars. When an electromag- 0010 Very dark gray 13.33
netic field that has a wavelength comparable to 0011 20.00
the conductor spacing passes through the plane
containing the conductors, diffraction occurs, 0100 Dark gray 26.67
producing an interference pattern. An adaptation 0101 33.33
of this device, called a DIFFRACTION GRATING, 0110 Medium-dark gray 40.00
is used to separate visible light into its con- 0111 46.67
stituent spectral colors.
1000 Medium gray 53.33
grating reflector A metal antenna reflector con-
1001 60.00
sisting of numerous parallel, straight, closely
1010 Medium-light gray 66.67
spaced conductors. When the conductor spacing
1011 73.33
is much smaller than the wavelength, the set be-
haves like a solid sheet of metal.
1100 Light gray 80.00
Gratz rectifier A form of full-wave rectifier circuit
1101 86.67
in a three-phase, alternating-current system.
1110 Off-white 93.33
gravitational constant Symbol, g. The accelera-
1111 White 100.00
tion produced by the attraction of a unit mass at
unit distance; g = 6.673 — 10“11 N•m2/kg2.
gravitational wave See GRAVITY WAVE. gray tin A form of tin that exhibits some properties
gravity 1. The universal force of attraction between of a semiconductor at temperatures below 18 de-
material bodies”especially that force evidenced grees Celsius.
greatest lower bound • grid resistor

greatest lower bound The largest value of a pa- grid-dip meter 1. A dip meter that contains a vac-
rameter that can be obtained without changing uum-tube oscillator; the indicating microammeter
some characteristic of a circuit, program, or sys- is in the grid circuit. 2. Loosely, any frequency-
tem. sensitive wavemeter that indicates resonance by a
Greek alphabet The 24-letter alphabet of the marked dip in input (base, grid, and gate) current.
Greek language. Virtually all of letters are used as grid-dip oscillator See GRID-DIP METER.
symbols in electronics and related sciences. grid dissipation 1. The amount of power given up
Green Book A specialized format for compact-disk as heat in the grid circuit of a vacuum-tube am-
read-only memory (CD-ROM) computer data stor- plifier. 2. The maximum amount of power that a
age media, developed by Sony and Philips. Re- tube can safely dissipate as heat in the grid.
quires the use of a Compact Disk-Interactive (CD-I) grid drive See GRID EXCITATION.
player for data retrieval. See also CD-ROM, OR- grid-driving power The signal power required by
ANGE BOOK, RED BOOK, and YELLOW BOOK. the control grid of a power tube.
green gun The electron gun in a color cathode-ray grid emission Electron or ion emission by the con-
tube whose correctly adjusted beam strikes only trol grid of a vacuum tube.
the green phosphors on the screen. grid excitation Signal voltage or power applied to
green video voltage In a three-gun color cathode- the control grid in a vacuum-tube amplifier cir-
ray-tube circuit, the green-signal voltage, which cuit.
actuates the green gun. grid impedance Symbol, ZG. The internal imped-
Greenwich Civil Time Abbreviation, GCT. Mean ance of the grid-cathode path in a vacuum tube.
time counted from mean midnight at Greenwich, grid input impedance The impedance of the grid
England, the location of zero meridian. input section of a vacuum-tube circuit. It is a
Greenwich Mean Time Abbreviation, GMT. Mean complex combination of grid impedance and the
solar time at zero degrees longitude, also called impedance of input-circuit components.
the Greenwich meridian because it passes gridistor A special form of field-effect transistor
through Greenwich, England. In recent years, with several channels.
GMT has been supplanted by COORDINATED grid-limiter resistor A resistor connected in series
UNIVERSAL TIME (UTC) as the basis of standard with the grid of a tube to limit grid current during
time throughout the world. the positive half-cycle of grid-signal voltage.
grid 1. The prime control electrode in a vacuum grid limiting The cutting off of plate current in a
tube. Usually, it is a coil or mesh, but it can have vacuum tube, with consequent limiting action, by
other forms. Also called control grid. 2. Any elec- means of a high, negative grid voltage developed
trode in a vacuum tube placed between the cath- by overdriving the grid.
ode and the anode (plate) (e.g., screen grid and grid loading effect The tendency of the internal
suppressor grid). 3. Two sets of straight, uni- grid-cathode path of a vacuum tube to load a
formly spaced, parallel conducting wires or rods, tuned circuit”especially when the grid draws
one set perpendicular to the other. The conduc- current.
tors are electrically connected at all crossing grid locking A vacuum-tube fault in which the grid
points. Used as an electrostatic or electromag- potential has become permanently positive be-
netic shield, or as a reflector of electromagnetic cause of excessive grid electron emission.
waves. 4. Two sets of uniformly spaced parallel grid mesh The mechanical structure of a grid (e.g.,
lines, one set perpendicular to the other, used as gauze or a metal screen).
a system of coordinates or as a basis for physical grid neutralization See GRID-NEUTRALIZED AM-
measurements. PLIFIER.
grid capacitor 1. A capacitor in series with the grid grid-neutralized amplifier A neutralized radio-
of a vacuum tube, used for blocking purposes. frequency power amplifier in which the neutraliz-
2. A bypass capacitor in a grounded-grid tube ing capacitor is connected from the plate of the
type amplifier. 3. The capacitor in the grid tank tube to the free end of a center-tapped grid-tank
circuit of a tube type oscillator or amplifier. coil.
grid-cathode capacitance Symbol, CGK. The in- grid north In the grid system of navigation, the di-
ternal capacitance between the control grid and rection most nearly corresponding to geographic
cathode of an electron tube. Also called INPUT north.
CAPACITANCE. grid-plate capacitance See PLATE-GRID CAPA-
grid characteristic The grid-current-versus-grid- CITANCE.
voltage performance curve for a vacuum tube. grid pool tube A gas-discharge tube in which the
grid circuit The external circuit associated with cathode is a pool of mercury.
the control grid of a vacuum tube. grid power loss Driving-power loss in the grid-
grid current Symbol, IG. Current flowing between input circuit of a power amplifier.
the control grid and cathode in a vacuum tube. grid resistor A high-value resistor connected be-
grid cylinder The metal cylinder that acts as a tween the control grid and ground in a vacuum-
control grid in a cathode-ray tube. tube amplifier circuit.
320 grid return • ground conduit

gross content The overall amount of data con-
grid return The circuit path through which the
tained in a message. It can be expressed in bits,
control grid of a vacuum tube is returned to
bytes, words, or other units.
ground or to the negative grid bias supply.
gross index One of a pair of indexes, used to give a
grid-separation circuit A vacuum-tube circuit
reference in the fine index, a supplement; both
in which the control grid is grounded. See
indexes are used to locate computer records in
grid swing The peak-to-peak variation of a grid
gross-motion planning The method(s) that a robot
excitation signal.
uses to navigate in a general area without run-
grid tank A resonant inductance-capacitance cir-
ning into objects, knocking things over, falling
cuit operating in the control-grid circuit of a vac-
down stairs, or losing its balance. It is often per-
uum tube. Compare PLATE TANK.
formed using a COMPUTER MAP of the work en-
grid tank capacitance The capacitance required
to tune a GRID TANK to resonance.
ground 1. The earth in relation to electricity and
grid tank inductance The inductance of the coil
magnetism. 2. An electrical connection to the
earth. 3. The return point in a circuit. 4. A short-
grid tank voltage The alternating-current (ac)
circuit to the earth or to a circuit return point.
voltage developed across the grid tank of a vac-
5. A short-circuit to the metal chassis, case, or
uum-tube circuit.
panel of a piece of equipment.
grid tuning Tuning of a vacuum-tube circuit by
ground absorption The absorption (and resulting
varying the capacitance, inductance, or both in
loss) of radio-frequency electromagnetic energy
by the earth.
grid voltage 1. Symbol, VG. The direct-current
ground bus A conductor connected to an earth
(dc) bias voltage applied to the control grid of a
ground, and to which devices in a system are in-
vacuum tube. 2. Symbol, VG(ac). The voltage of
dividually connected. The common ground points
the radio-frequency (RF) or audio-frequency (AF)
(e.g., chassis) of the individual devices are not di-
signal in the grid circuit.
rectly connected to each other, so ground loops
grille A covering for an acoustic speaker, used
are avoided. This scheme minimizes the probabil-
primarily to protect the speaker cone, but also
for esthetic appeal.
or from the system. Compare GROUND LOOP.
grille cloth A durable fabric often used for
speaker grilles in high-fidelity sound systems. It
transmits sound at all audio frequencies, but
protects the speaker(s) and provides an attrac-
tive physical appearance.
gripper See ROBOT GRIPPER.
grommet An elastic washer inserted through a
hole in a chassis to prevent accidental ground-
ing of a conductor or to reduce wear on a cord or
cable exiting the chassis. Bus
groove 1. See KEYWAY. 2. The fine, spiral line
cut into a phonograph disc when it is manufac- ground bus
groove angle On a phonograph disk, the angle
between the walls of the unmodulated groove. ground clamp A device that provides a mechanical
and electrical bond between a conductor and a
ground rod or pipe. It is generally capable of pass-
ing a large amount of current.
surface ground clutter 1. In a surface-based radar sys-
tem, echoes from nearby buildings, hills, and
other objects, producing blips or blobs near the
θ = Groove angle
Disk θ
center of the screen. 2. In radar operations, an in-
motion: (usually 90°)
terference pattern on the screen, caused by acci-
toward observer
dental grounding in the system.
ground conductivity The ease with which the
groove angle
earth will carry electrical current. Saltwater has
the best conductivity; dark, moist soil and fresh
groove speed In a phonograph recording or repro- water (because of the mineral content) rate from
ducing system, the speed of the cutter or needle, fair to good. Sandy soil has the poorest ground
with respect to the disc. The speed is greatest conductivity.
near the outer edge of the disk, and least near the ground conduit A pipe housing one or more
center. ground leads.
ground connection • ground-mounted vertical antenna

ground connection 1. A low-resistance connec- ground efficiency In an antenna system, the qual-
tion to the earth. 2. The common point, such as a ity of the ground circuit. For some antenna sys-
chassis, to which zero-potential terminals of cir- tems, such as a balanced dipole at great height,
cuit components are connected. this is not a consideration. Ideal ground efficiency
ground constants The conductivity and dielectric (100%) results in zero ground loss.
constant of the earth for a particular kind of ter- ground environment 1. See GROUND CON-
rain and soil at a given location. Affects the be- STANTS. 2. The ground characteristics in the
havior of radio antenna systems and electrical vicinity of an unbalanced antenna working
utility systems. Usually, high conductivity (low against ground. 3. In aviation, the set of ground-
resistance) and low dielectric constant are desir- based installations.
able characteristics. ground fault 1. Loss of a ground connection. 2. A
ground-controlled approach Abbreviation, GCA. short-circuit to ground.
In air navigation, a ground radar system that pro- ground-fault interrupter Abbreviation, GFI. A
vides information for radio-directed aircraft ap- fast-acting electronic circuit breaker that opens
proaches. the power-line circuit breaker to prevent electric
ground-controlled interception Abbreviation, shock or equipment damage when the path of
GCI. A ground radar system by which an aircraft current flow is through the earth.
can be directed to intercept enemy aircraft. grounding electrode A device, such as a ground
ground current 1. A direct electric current flowing plate or ground rod, that facilitates low-
into the earth from an electrical or electronic de- resistance connections to the earth.
vice, or into a device from the earth. 2. An alter- grounding plate A metal plate connected to the
nating current flowing between the earth and a earth, on which a person stands to discharge
device. 3. An electric current flowing through the static electricity from the body.
earth between two points. 4. A current flowing in grounding rod See GROUND ROD.
the normal ground (low-potential) line of a circuit. ground insulation Electrical insulation used be-
ground detector A device that indicates whether tween adjacent energized and grounded parts,
or not a given circuit point is at direct-current such as transformer windings and metal cores.
ground. ground level See GROUND STATE.
grounded antenna See MARCONI ANTENNA. ground loop A closed current path resulting from
grounded-base circuit See COMMON-BASE CIR- improper grounding of the components in a sys-
CUIT. tem. A loop is formed when two devices are con-
grounded-cathode circuit See COMMON- nected to each other, and also to separate earth
CATHODE CIRCUIT. grounds or to a single earth ground via conductors
grounded-collector circuit See COMMON- of appreciable length. The loops can act as anten-
COLLECTOR CIRCUIT. nas, increasing the likelihood of ELECTROMAG-
grounded-drain circuit See COMMON-DRAIN NETIC INTERFERENCE to or from the system. The
CIRCUIT. use of a single GROUND BUS is preferred.
grounded-emitter circuit See COMMON-
grounded-gate circuit See COMMON-GATE CIR-
grounded-grid circuit See COMMON-GRID CIR- A B C
grounded outlet An outlet with a receptacle hav-
ing a ground contact that can be connected to
equipment-grounding conductors.
Loop Loop
grounded-source circuit See COMMON-SOURCE
grounded system A set of electrical conductors or
a transmission line in which one conductor is de-
liberately grounded. ground loop
ground effect 1. Modification or distortion of the
ideal free-space directivity pattern of an antenna
by reflections from, and absorption by, the earth. ground mat A grid or network of conductors, con-
2. Effects of the earth on radio-wave propagation nected to earth ground, for the purpose of im-
(e.g., the production of a reflected wave and a sur- proving the earth conductivity.
face wave, neither of which can exist if the earth ground-mounted vertical antenna A vertical radi-
is not part of the signal path). 3. Effects on an- ator mounted at the earth™s surface or at the sur-
tenna behavior, such as modification of the face of a body of water, and fed with coaxial cable.
impedance and resonant frequency, caused by The radiator can be any physical length, but it is
the proximity of the earth. tuned to resonance at the operating frequency.
322 ground-mounted vertical antenna • groundtrack

The center conductor of the cable is connected to ground plate A metal plate buried in the earth to
the base of the radiator, and the shield is con- provide a low-resistance ground connection.
nected to a ground system. Radial wires, usually ground-position indicator Abbreviation, GPI. A
buried just below the surface, minimize losses. computer system that gives a continuous indica-
The antenna can be made resonant on several tion of an aircraft™s position in terms of heading,
frequencies by inserting multiple loading coils or elapsed time, and speed, with respect to the sur-
traps in the radiator. The chief advantages of this face. This provides a more useful indication of the
antenna are unobtrusiveness and ease of instal- aircraft position than an air-speed indicator be-
lation. The main problems are marginal efficiency cause it is not affected by high-altitude winds.
and susceptibility to human-made electro- ground potential See ZERO POTENTIAL, 3.
magnetic noise. See also RADIAL, 1. Compare ground protection The use of a GROUND-FAULT
ground noise 1. Electrical noise that results from ground-reflected wave A radio wave component
a faulty ground connection. 2. Background noise. that results from ground reflection.
3. In wire circuits, such as a telephone system, ground reflection The reflection of a radio wave by
electrical noise that results from fluctuations in the earth.
ground current. ground resistance The direct-current resistance of
ground plane 1. A metal plate or a system of hori- a connection to the earth, or the resistance be-
zontal rods or wires mounted high on a mast, at tween two points through the earth. The magni-
the base of a vertical antenna, to provide a radio- tude of the resistance depends on several factors:
frequency ground at a point several wavelengths composition of the soil, amount of moisture, soil
above the surface of the earth. Also see GROUND- electrolytic action, and the area of contact with
PLANE ANTENNA. 2. In noise and interference the earth.
tests, a sheet metal structure used to simulate ground return 1. The point or path used to return
the skin of an aircraft or missile. 3. On a circuit a circuit to ground for completion. 2. In radar,
board, a thin metallic sheet, usually bound to the echoes returned from the earth™s surface (includ-
underside, that serves as a common ground and ing reflections from objects on it).
RF shield. ground-return circuit A circuit, such as a single-
ground-plane antenna A vertical radiator oper- wire telephone line, in which earth ground forms
ated against a system of quarter-wave radials, one leg of the circuit. Compare METALLIC CIR-
elevated at least a quarter wavelength above the CUIT.
earth™s surface and fed with coaxial cable. ground rod A strong metal rod driven deep into the
The center conductor of the cable is connected earth as a point of ground connection.
to the base of the radiator, and the shield is con- ground speed The speed of an aircraft or missile,
nected to three or four quarter-wave radials that relative to the surface of the earth.
run outward from the base of the radiator. At ground state The least-energy level of all possible
shorter wavelengths, a disk or cone can replace states in a system.
the radials. The chief advantages of this an- ground support equipment Electronic surface-
tenna are simplicity and high efficiency. The based apparatus upon which the functioning of a
main problem is susceptibility to human-made weapons system is dependent.
electromagnetic noise. See also RADIAL, ground switch A switch for grounding an outside
1. Compare GROUND-MOUNTED VERTICAL antenna during idle periods. Also called lightning
ANTENNA. switch. Ideally, antennas should be disconnected
from equipment, as well as grounded, when not
in use.
ground-to-air communication Radio or radar
transmission from a land station to an aircraft in
ground-to-ground 1. Pertaining to communica-
tions between land-based stations. 2. Pertaining
to missiles intended for use between points on
the surface of the earth.
ground-to-ground communication Communica-
tions between land-based stations.
groundtrack For an earth-orbiting satellite, the
path followed by the point on the earth™s surface
from which the spacecraft appears directly over-
head. For most satellites, this path shifts toward
the west for each succeeding orbit, because the
earth rotates eastward underneath the satellite.
For geostationary satellites, the point never
groundtrack • G-string antenna

changes position on the surface. For satellites in Platinum
equatorial orbits, the track follows the equator. (+)
ground wave In wireless communications and
broadcasting, an electromagnetic (EM) wave that
consists of three distinct components: the direct Porous cup
wave (also called the line-of-sight wave), the re-
flected wave, and the surface wave. The direct
wave is significant only when the transmitting and Sulfuric
receiving antennas are connected by a line through
free space without obstructions. The reflected
wave, after returning from the earth™s surface or a Grove cell
human made structure, combines with the direct
wave (if any) at the receiving antenna. The surface
growler 1. An electromechanical troubleshooting
wave travels in electrical contact with the earth.
device that indicates the location of short circuits
This occurs only with vertically polarized EM fields
and grounds (especially in electric motors) by
at frequencies below about 15 MHz. Below about
emitting a growling or rumbling sound. 2. Any
300 kHz, the surface wave propagates for hun-
tester that provides an audible signal, which indi-
dreds or even thousands of miles. Sometimes the
cates electrical continuity.
surface wave is called the ground wave.
grown-diffused transistor A transistor that is
ground wire A conductor between an equipment
made by first growing the emitter and collector
and a ground connection, either for circuit com-
regions as a crystal, into which the base region is
pletion or for safety.
later diffused while the crystal is being pulled.
group 1. A series of computer storage locations
grown diode A semiconductor diode created by
containing a specific record or records. 2. The
growing a layer of p-type material into n-type ma-
data in these locations. 3. A record set having a
terial (or vice versa) as the single-crystal material
common key value in a sorted file.
is being pulled from the melt.
group busy In a telephone system, an audio signal
grown junction A pn junction produced by adding
indicating that all of the lines in a group are in
impurities in various amounts to a crystal while it
is being pulled from molten semiconductor mate-
group code In digital communications, an error-
detecting code used to verify a character group
grown-junction diode See GROWN DIODE.
transferred between terminals.
grown-junction photocell A grown-junction diode
group delay In a modulated signal, a delay in the
used as a photoconductive cell.
transmission of data.
grown-junction transistor A transistor made by
grouped-frequency operation In a two-wire com-
adding n-type and p-type impurities succes-
munications system, the grouping of directional
sively to a crystal in its molten state, then slicing
signals into certain frequency bands.
the resulting npn formations from the finished
grouped records A set of data records in which the
key of one record identifies the entire set.
G-scan A rectangular radar display consisting of a
grouping 1. The arrangement of data into blocks
laterally centered blip that “grows wings” as a tar-
or sets. 2. On a phonograph disc, the insertion of
get approaches. Horizontal and vertical displace-
gaps in the arrangement of grooves. 3. Any peri-
ment of the blip indicate horizontal and vertical
odic irregularity in the spacing of a data trans-
aiming errors.
mission. 4. The bunching of grooves on a disc
G scope See G SCAN.
recording. 5. In a facsimile system, occasional
spacing errors between recorded lines. 6. A mass
G-string antenna In microwave operations, a com-
of data arranged into groups, according to com-
munications path provided by a dielectric-coated
mon characteristics.
wire that behaves like an extremely low-loss
group mark 1. In telegraphy, an indicator that sig-
coaxial line with its outer conductor removed to
nals the end of a data unit. 2. A character indi-
infinity. A horn at each end matches the line to
cating the end of a character group; usually, it is
the transmitter and receiver. The term comes
a logical record that is addressed and processed
as a unit.
group velocity The velocity at which a group of
waves or a pulse is propagated. Transmitting Receiving
Grove cell A closed-circuit primary cell in which horn horn
the positive electrode, platinum, is immersed in
nitric acid; the negative electrode, zinc, is im- Coaxial Coaxial
mersed in sulfuric acid. The nitric acid is held in cable cable
a porous cup, surrounded by a larger jar of sulfu-
ric acid. G-string antenna
324 G-string antenna • Gunnplexer

from the first initial of Dr. George Groubau, in- control station or by sensing equipment aboard
ventor of the device, and the stringy appearance the missile.
of the wire. guided propagation A form of radio-wave propaga-
GTO Abbreviation of GOTO. tion in which air masses of different temperatures
guard band A narrow unoccupied band of frequen- or humidity levels cause refraction and/or reflec-
cies at the upper and lower limits of an assigned tion of electromagnetic waves, guiding signals
channel; its purpose is to prevent adjacent- over long distances with very little attenuation.
channel interference by ensuring adequate Commonly observed at very-high and ultra-high
separation between channels. frequencies.
guard circle On a phonograph disk, an inner guide elbow See WAVEGUIDE ELBOW.
groove that prevents collision of the pickup with guide flange See WAVEGUIDE FLANGE.
the spindle at the center of the disc. guide gasket See WAVEGUIDE GASKET.
guard circuit An auxiliary circuit added to an guide junction See WAVEGUIDE JUNCTION.
alternating-current bridge to compensate for the guide load See WAVEGUIDE LOAD.
effects of stray capacitance in the bridge arms. guide slot See KEYWAY.
One of its several forms is the WAGNER guide wavelength See WAVEGUIDE WAVE-
guarded input An input-terminal arrangement in Guillemin effect The tendency for a strip of ferro-
which one terminal, maintained at the proper po- magnetic material to become straight in a strong
tential, shields the entire input-terminal combi- magnetic field. This is a form of MAGNETO-
nation. STRICTION.
guarding A method of short-circuiting a leakage Guillemin line In radar operations, a special
current to ground. On a printed-circuit board, pulse-forming network for controlling modulation
guarding is usually accomplished by the use of a pulse duration.
large conducting foil surface near critical compo- guillotine capacitor A variable capacitor in which
nents. a sliding (instead of rotary) plate moves between
guard relay A relay that ensures that only one two stator plates. Its name results from its re-
linefinder will be connected to a line circuit when semblance to the infamous beheading apparatus.
other line relays are in operation. gulp Several bytes of digital information.
guard ring A metal ring (or other configuration) gun See ELECTRON GUN.
surrounding, but separate from, a charged body Gunn diode A semiconductor diode that can oper-
or terminal, for the purpose of evenly distributing ate as an oscillator in the ultra-high-frequency
the electric charge over the latter™s surface. (UHF) and microwave parts of the radio spec-
guard shield A shield that encloses the input cir- trum. Oscillation takes place as a result of a neg-
cuit of an amplifier or instrument. ative-resistance effect in which, within a certain
guard terminal In a GUARDED INPUT, the termi- range of applied voltages, the current decreases
nal that shields the combination. as the voltage increases. The device is not partic-
guard wire A grounded wire that is intended to ularly efficient. Only a small fraction of the input
catch and ground a broken high-voltage line. power results in useful signal output. The fre-
Gudden-Pohl effect The tendency of an ultraviolet quency and oscillation stability are sensitive to
irradiated phosphor to glow momentarily when changes in temperature and bias voltage. See
subjected to an electric field. GUNN EFFECT, NEGATIVE RESISTANCE.
GUI Acronym for GRAPHICAL USER INTERFACE. Gunn effect A semiconductor phenomenon named
Can be spelled out or pronounced “gooey.” after J. Gunn of International Business Machines
guidance Electronic control of the path or course (IBM) who first observed and studied it in the
of a robot, missile, or other vehicle. 1960s. In certain types of diodes having a nega-
guidance system The complete electromechanical tive-resistance characteristic, oscillation occurs
system for control of a robot, missile, or other ve- when the applied voltage is within a certain
hicle. It consists of hardware and software. The range. See GUNN DIODE, NEGATIVE RESIS-
hardware includes beacons, sensors, drive sys- TANCE.
tems, rockets, etc. The software interprets data Gunn-effect circuit Any circuit exploiting the
from, and transmits commands to, the hardware. Gunn effect, especially a GUNN OSCILLATOR.
The nature of the hardware and software depend Gunn oscillator A discrete semiconductor mi-
on the application. crowave oscillator using a GUNN DIODE.
guidance tape In a guided missile, a magnetic tape Gunnplexer A microwave transmitter consisting of
containing computer instructions for steering the a Gunn-diode oscillator connected to a horn an-
missile in a designated course. tenna. Usually, the entire device is a compact,
guide See WAVEGUIDE. self-contained unit. The output power is low.
guide connector See WAVEGUIDE CONNECTOR. When the device is placed at the focal point of a
guided missile A missile whose progress to a tar- large dish antenna with the horn pointing toward
get is controlled electronically by signals from a the dish reflector (conventional dish feed), consid-
Gunnplexer • G-Y signal

erable transmission range is possible. Used pri- guy wire A bracing wire for antenna masts or tow-
marily by experimenters, and in wireless commu- ers.
nications links. See GUNN DIODE. gyrator An active (usually cascaded-transistor) de-
gutta percha A hard, rubberlike, organic insulat- vice exhibiting nonreciprocal phase shift. It pro-
ing material. Dielectric constant, 3.3 to 4.9. Di- vides, among other functions, the simulation of
electric strength, 203 to 508 kV/in. inductance using capacitors.
guyed tower In radio communications or in mi- gyro Contraction of GYROSCOPE.
crowave links, a structure that is supported by gyro- A prefix meaning “pertaining to gyroscopes,”
one or more sets of guy wires to add strength and “containing a gyroscope,” or “behaving like a gy-
to prevent collapse. roscope.”
guying The support of a radio communications or gyrocompass A type of compass in which a spin-
microwave-link tower by the use of one or more ning gyroscope, acted upon by the earth™s rota-
sets of guy wires. tion, causes the device to point to true north.
guy insulator Also called egg insulator. An insula- Compare MAGNETIC COMPASS.
tor designed to electrically break a guy wire while gyrofrequency The natural frequency of rotation
maintaining its ability to support a structure. of charged particles around the earth™s magnetic
Such an insulator has two slots with holes placed lines of flux.
at right angles, in such a position that the wire gyromagnetic Pertaining to the magnetic proper-
will not separate even if the insulator breaks. The ties of rotating electric charges (e.g., the effect of
stress exerted on the insulator is compression, electrons spinning inside an atom).
and the insulating material is stronger under this gyromagnetic effect The tendency of a rotating
type of stress than under tension (pulling). body to become magnetized because of the mag-
netic field of the earth.
gyropilot See AUTOPILOT.
gyroscope A device that consists of a spinning
wheel mounted in a gimbal. The shaft of the
wheel will point in one direction, despite the
movement of the earth beneath it.
gyrostat See GYROSCOPE.
G-Y signal In a color-television circuit, the signal
representing primary green (G) minus luminance
(Y). A primary green signal is obtained when the
G-Y signal is combined with the luminance (Y)
guy insulator signal. Compare B-Y SIGNAL and R-Y SIGNAL.
hairline A fine line used as an index or a graticule
H 1. Symbol for magnetic field strength. 2. Symbol
marker in a precision instrument.
hairpin coil A quarter-turn coil, so called from its
GEN. 4. Symbol for UNIT FUNCTION. 5. Abbrevia-

resemblance to a hairpin.
tion of HORIZONTAL. (Also, hor and horiz.)
hairpin coupling coil A hairpin coil used as a low-
6. Symbol for HENRY. 7. Symbol for HARMONIC.
impedance primary or secondary coil for input or
h 1. Abbreviation of prefix HECTO-. 2. Symbol for
output coupling.
the PLANCK CONSTANT. 3. Abbreviation of HOUR.
hairpin match A form of impedance-matching net-
Haas effect See FUSION, 1.
work used at the feed point of a half-wave dipole
hack In computer networking, to access, and
antenna. A short length of open-wire transmis-
sometimes to change, sensitive data without au-
sion line, short-circuited at the far end, is con-
nected in parallel with the antenna at the feed
hacker A person knowledgeable in computer net-
working who uses his or her expertise to access,
hairpin pickup A short, doubled length of wire
and sometimes alter, sensitive data. This is illegal
that acts as a pickup coil at very-high and ultra-
and can sometimes be destructive. The intent, is
high frequencies.
rarely malicious, however, the activity is viewed
hairspring A fine, usually spiral spring”espe-
as a challenge. Compare CRACKER.
cially the one in a movable-coil meter or the one
HACKER program A computer program developed
connected to the balance wheel of a watch or
by Gerry Sussman as an early experiment with
artificial intelligence (AI), to see how the machine
hair-trigger Pertaining to extreme sensitivity of re-
would deal with complex decision-making prob-
sponse, such as the tendency of a switching de-
vice to change state when excited by a weak
hadron A subatomic particle consisting of quarks.
hafnium Symbol, Hf. A metallic element. Atomic
hair wire 1. An extremely thin wire filament in a
number, 72. Atomic weight, 178.49. Readily
lamp or bolometer. 2. Very small gauge wire (e.g.,
emits electrons.
hahnium See DUBNIUM.
hal Abbreviation of HALOGEN.
hailer 1. A marine microphone-amplifier-speaker
half-add The sum of two binary digits, in which the
system for calling to other boats or persons
carry operation is omitted. Thus 0 + 0 = 0, 0 + 1 =
ashore. 2. A comparable system for land vehicles,
1, 1 + 0 = 1, and 1 + 1 = 0.
such as police cars. Also see MEGAPHONE, 1.
half-adder In digital systems, an adder circuit that
hair See HAIRLINE.
can handle the two binary bits that are to be
hair hygrometer A device for measuring rela-
added, but that cannot accommodate a carry sig-
tive humidity, in which a stretched hair is the
nal. Compare FULL ADDER.
moisture-sensitive element.

Copyright © 2001 by The McGraw-Hill Companies, Inc.
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half-bridge • half-wavelength

half-power width In a directional antenna system,
an expression of beamwidth. It is usually listed as
the horizontal-plane angle, in degrees, between
Sum output the half-power points in the main lobe of the di-
rective pattern.
half-step 1. In audio engineering, the frequency
interval between two sounds, whose ratio is
1.06:1. 2. The difference in pitch between the
notes produced by two adjacent keys on a
half tap A bridging circuit or device that can shunt
another circuit with the least electrical distur-
Carry output
half-track recorder A magnetic tape recorder that
applies signals to both halves of a tape with a
half-adder head that covers only half the tape™s width in
each of two directions. Also called dual-track
half-track tape Magnetic tape recorded by a
half-wave Half of a complete wave (i.e., a complete
rise and fall in one direction). Its graphic repre-
ac + sentation is similar in appearance to that for a
half-wave antenna An antenna whose radiator
measures an electrical half wavelength from end
to end. Such a radiator is about 5 percent less

than a free-space half-wavelength long, because
of capacitive effects and the velocity factor of the
half-wave chopper A chopper that closes a circuit
during only half the switching signal cycle.
half-wave dipole A center-fed antenna whose radi-
half-bridge A bridge rectifier that has diodes in two
ator measures 0.5 electrical wavelength from end
arms and resistors in the other two.
to end. Also see DIPOLE ANTENNA.
half-cell A voltaic cell consisting of a single elec-
half-wave doubler See HALF-WAVE VOLTAGE
trode immersed in an electrolyte and having a
definite difference of potential; it is, in effect, half
half-wave feeder See HALF-WAVE TRANSMIS-
of a primary cell. Also see HELMHOLTZ DOUBLE
half-wavelength Symbol »/2. The distance that
half-cycle Half of a complete alternation (i.e., 180
corresponds to 180 degrees of phase as an elec-
degrees of phase).
tromagnetic (EM) field is propagated in free
half-cycle magnetizer A magnetizer using half-
space, it is related to the frequency by a simple
cycles of rectified alternating current as the mag-
netic-field source.
half-duplex channel A communications channel L ft = 492/f
where Lft represents »/2 in feet, and f represents
half-duplex system In data communications, a
the frequency in megahertz. If »/2 is expressed in
system that transmits data in both directions,
meters, then the formula is:
but not simultaneously. Compare FULL-DUPLEX
SYSTEM. L m = 150/f
half-lattice crystal filter A band-pass crystal-
where Lm represents the displacement in meters.
filter circuit using two piezoelectric crystals
In general, if ν is the velocity factor (expressed as
in a four-arm bridge. Also see CRYSTAL RES-
a ratio) in a given medium, then:
L ft = 492ν/f
half-nut In a facsimile receiver, a device that
guides the lead screw.
half-power point In a response curve or direc-
L m= 150ν/f
tional pattern, such as for a selective filter or a
unidirectional antenna, the points on each side of
maximum at which the power is 3 dB below the Compare FULL WAVELENGTH, QUARTER
peak value. WAVELENGTH.
328 half-wave loop antenna • Hall field

half-wave loop antenna A loop antenna having a half-wave vibrator A vibrator (see INTERRUPTER)
circumference of 0.5 wavelength with a break op- whose reed operates against only one stationary
posite the feed point. It is, in effect, a HALF-WAVE contact. Compare FULL-WAVE VIBRATOR.
DIPOLE bent into a circle or square (although any half-wave voltage doubler A voltage-doubler cir-
symmetrical configuration can be used). The cir- cuit whose direct-current (dc) output has a ripple
cle is the most efficient configuration. frequency equal to that of the alternating-current


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