. 19
( 42)


(ac) supply. Although its output is harder to filter
than that of a full-wave doubler, this circuit has
Gap the advantage of a common ground. Compare

»/4 »/4 100 V D2
’ +
200 Vdc
100 Vac C2

half-wave loop antenna

half-wave voltage doubler
half-wave radiator An antenna consisting of a sin-
gle, usually straight, active element that mea-
sures an electrical half wavelength from end to halide A compound of a HALOGEN. Examples:
end. It is therefore a resonant element. A simple sodium iodide, used as a scintillating crystal; am-
half-wavelength (»/2) conductor with a high monium chloride, used as the electrolyte in a dry
length-to-diameter ratio measures approximately cell.
95 percent of »/2 in free space. The element can be halide crystal A halogen-compound crystal, such
much shorter than free-space »/2 yet remain »/2- as mercuric iodide and sodium iodide, useful in
resonant if inductance is inserted in series with detecting radioactivity.
the radiator. The element can be much longer Hall coefficient For a current-carrying conductor,
than free-space »/2 yet remain »/2-resonant if dis- the constant relationship between the Hall
tributed capacitances are inserted in series with (transverse electric) field and the magnetic flux
the radiator. density.
half-wave rectification The conversion of alter- Hall constant For a current-carrying conductor,
nating current (ac) to direct current (dc) during the constant of proportionality k given by the
half of each ac cycle. Also see HALF-WAVE REC- equation k = e/(im), where e is the transverse
TIFIER. electric field (Hall field), i is the current density,
and m is the magnetic field strength.
Hall effect A phenomenon observed in thin strips
of metal and in some semiconductors. When a
strip carrying current longitudinally is placed in a
magnetic field that is perpendicular to the strip™s
plane, a voltage appears between opposite edges
of the strip that, although feeble, will force a cur-
rent through an external circuit. The voltage is
positive in some metals (such as zinc) and nega-
tive in others (such as gold). Also see ETTING-
half-wave rectifier A rectifier that delivers a half- HAUSEN EFFECT, NERNST EFFECT, and
cycle of direct-current (dc) output for every other RIGHT-LEDUC EFFECT.
half-cycle of applied alternating-current (ac) volt- Hall-effect modulator A device that uses the HALL
age. Because the successive dc half-cycles are EFFECT to modulate a signal, or to mix two sig-
180 degrees apart, they have the same polarity. nals.
Compare FULL-WAVE RECTIFIER. Hall-effect multiplier A device based upon the
half-wave transmission line A transmission line Hall generator and used in analog mathematical
measuring 0.5 electrical wavelength at the trans- operations, such as multiplication and the ex-
mission frequency. The physical length is some- traction of roots.
what less than a free-space half wavelength Hall field The transverse electric field of a conduc-
because of the VELOCITY FACTOR of the line. tor carrying current in a magnetic field.
Hall generator • handoff

Hall generator A semiconductor device exhibiting ends are capacitance loaded. Commonly used at
the HALL EFFECT. It is a thin wafer or film of in- very high frequencies (VHF).
dium antimonide or indium arsenide with leads halogen Abbreviation, hal. A group of five very ac-
on opposite edges. tive nonmetallic elements whose similar chemical
properties put them in group VIIA of the periodic
table; they are astatine, bromine, chlorine, fluo-
rine, and iodine.
Hall current
Halowax A chlorinated naphthalene wax used as
Magnetic field
an impregnant for paper capacitors. Dielectric
constant, 3.4 to 5.5. Resistivity, 1013 to 1014 ohm-
to ohmic
halt A stop during the execution of a computer
program run, often resulting from a HALT IN-
Control halt instruction An instruction in a computer pro-
gram that causes a break in the program™s execu-
tion, as by BASIC™s STOP command, for example.
Ohmic ham Colloquialism for AMATEUR RADIO operator.
ham radio See AMATEUR RADIO.
Hamilton™s principle Also called the principle of
least action. Motion tends to occur in such a
Control current
way that the integral of the product of kinetic en-
ergy and elapsed time is minimal.
Hall generator
hammer 1. The striking member in a WHEEL
PRINTER. 2. The clapper in an electric bell or
Hall mobility For a conductor or semiconductor, gong.
the product of conductivity and the HALL CON- hammer-and-wheel See WHEEL PRINTER.
STANT. Hamming code An error-correction code used in
Hall network A resistance-capacitance null circuit some digital communications circuits.
whose general configuration is two cascaded hand capacitance Also called body capacitance.
high-pass tee-sections bridged by a high resis- Capacitive coupling effects between a circuit and
tance. The circuit can be tuned with one poten- the human body (e.g., as evidenced between an
tiometer. operator™s hand and a device having extremely
high impedance and poor grounding and/or
R1 hand generator An electric generator operated by
turning a hand crank.
handheld computer Also called personal digital
C1 C2 C3 assistant (PDA) or palmtop computer. The names
PalmPilot and Palm are proprietary (Palm Com-
puting, Inc.) and refer to specific families of hand-
held computers, although they might someday
Input Output become generic and refer to handheld computers
R2 R3 in general. A battery-powered portable computer,
smaller than a notebook computer, and used
for simple tasks such as note-taking and
record keeping. Some units incorporate wireless
modems for connection to the Internet. Others in-
Hall network
clude paging, wireless fax, videoconferencing ca-
pability, remote-control capability, and other
features. Many units can recognize a specialized
Hallwacks effect The phenomenon (observed by
form of handwriting so users can enter data with
Hallwacks in 1888) in which ultraviolet light
a penlike device called a stylus.
falling on a polished zinc plate causes a nega-
Handie-Talkie Abbreviation, HT. Tradename for a
tively charged electroscope to which it is con-
portable transceiver small enough to be held in
nected to discharge.
the hand during operation.
hallucination In complex computers and artifi-
hand key Also called brass pounder. An old-
cially intelligent systems, the generation or ap-
fashioned, hand-operated telegraph key, oper-
pearance of data for no apparent reason.
ated by manual downward pressure.
handoff In cellular communications networks, the
halo antenna A horizontally polarized antenna,
changeover of reception from, and transmission
consisting of a circular half-wave dipole whose
330 handoff • hard-wire telemetry

hard dump See HARDWARE DUMP.
to, a mobile or portable set from one repeater to
hard magnetic material High-retentivity magnetic
another as the subscriber moves from one cell
material. Also see RETENTIVITY.
into another. When the subscriber is moving
hardness 1. The property that causes a material to
rapidly”for example, driving along a freeway,
resist penetration, deformation, scratches, etc. 2.
such transfers occur relatively often. When a
The penetrative ability of ultraviolet rays, X rays,
subscriber is moving slowly, for example, walking
or other ionizing radiation. Generally, the radia-
along a trail, such transfers occur rarely. When a
tion hardness increases as the wavelength de-
subscriber is in a fixed location, such transfers
creases, and as the photon or particle energy
do not normally occur.
hand-operated device A device manipulated di-
hardness tester A device for measuring the hard-
rectly and manually by the operator™s hand(s).
ness of a solid in terms of the force required to
Also called manual device.
penetrate its surface. Also see HARDNESS, 1.
hand receiver 1. A single earphone that must be
hard radiation In general, any radiation with high
held against the ear. 2. A telephone receiver.
penetrating power. Usually, this term is used in
reference to short-wavelength (high-energy) ultra-
violet rays or X rays.
hard solder Solder that melts at a comparatively
handset See CRADLEPHONE.
high temperature. Compare SOFT SOLDER.
handshaking 1. A controlled, periodic exchange of
hard vacuum A nearly perfect vacuum, that is, a
synchronizing pulses between a digital transmit-
medium essentially devoid of atomic or sub-
ter and receiver. 2. In a digital communications
atomic particles.
system, a method of error correction. The receiver
hardware 1. Collectively, electronic circuit compo-
detects nonstandard or improbable character se-
nents and associated fittings and attachments. 2.
quences, and instructs the transmitter to repeat
In a computer system, the electronic and elec-
them for double-checking.
tromechanical components (e.g., integrated cir-
hand-type pointer In an electric meter, a spear-
cuits, keyboards, and disk drives) associated with
like pointer (resembling the hand of a clock), as
operation. Compare SOFTWARE.
opposed to a knife-edged pointer.
hardware availability ratio A figure depicting the
hand-wired Pertaining to electronic equipment
availability of a computer system to do productive
wired by hand, rather than being assembled on
work; as a percentage, it is given by the formula:
printed-circuit boards. This form of construction
is rarely seen nowadays, except in some radio-
A = 100(ta “ td)/ta,
frequency power amplifiers.
where A is the availability ratio, ta is the opera-
hang AGC An automatic-gain-control (AGC) circuit
tional time, and td is the downtime over a speci-
whose action is sustained for a brief interval after
fied time period.
an actuating signal has passed, an advantage in
hardware check A check on data being transferred
some applications. Also called fast-attack/slow-
within a computer, as done by hardware (e.g., a
release AGC.
parity check).
hangover In sound operations, the blurring or
hardware cloth A finely woven wire screen some-
smearing of low-frequency (bass) notes by a
times used in place of a metal plate for an an-
poorly damped or poorly mounted loudspeaker.
tenna element, an antenna reflector, or a shielded
hangup 1. In phonograph operation, the state in
enclosure. Especially useful when free-air circu-
which the same material is played repetitiously
lation is required.
(i.e., the stylus does not move toward the spin-
hardware dump During a computer program run,
dle). 2. In digital-computer operations, an unex-
data sent to a storage device for later evaluation;
pected break during a program run as a result of
it occurs at the time of a failure. Also called AU-
software or hardware failure. Sometimes called
hardware engineer A person who designs and per-
H antenna See LAZY-H ANTENNA.
fects the actual electronic circuitry in a system.
hard copy 1. In digital computer operations, a
The hardware engineer is not involved with the
readable document (printout) of material being
programming of the system.
translated to a form understood by a computer.
hardware recovery A computer system™s ability
2. Generally, written or typed documents, as op-
(through software or hardware) to recover from a
posed to data on other media, such as diskettes,
failure (i.e., to proceed from the point of failure).
tapes, CD-ROM, etc.
hardware serviceability ratio See HARDWARE
hard disk An electromechanical data storage me-
dium commonly used in personal computers.
hardwire 1. To construct a circuit for direct-current
Consists of several rigid disks, called platters,
conductivity. 2. A circuit exhibiting direct-current
coated with ferromagnetic material.
conductivity over a complete, closed path.
hard-drawn wire High-tensile-strength unan-
hard-wire telemetry See WIRE-LINK TELEMETRY.
nealed wire.
hard wiring • harmonic-distortion percentage

hard wiring 1. In computer systems, functions or harmonically related bands In communications,
programs built directly into the machine hard- frequency bands arranged so that the frequencies
ware. In order to alter such functions or pro- in one band are harmonics of the frequencies in
grams, the system wiring and/or components another band. An example of bands that are pre-
must be physically changed. 2. A system inter- cisely related in this way are 4.1 to 4.3 MHz and
connected entirely by wires and cables, and using 8.2 to 8.6 MHz. Various amateur radio bands are
no free-space links, such as radio or infrared. harmonically related to some extent, such as 40
hard X rays High-frequency (shortwave) X rays. meters (7.0 to 7.3 MHz) and 20 meters (14.0 to
Such radiation has high penetrating power. Com- 14.35 MHz).
pare SOFT X RAYS. harmonic amplifier An amplifier, such as one
harmonic 1. Symbol, H. In a complex sound or sig- used with a frequency standard, used to increase
nal wave, a component whose frequency is a mul- the amplitude of weak harmonics. Also see HAR-
whole-number factor of 2 or more. 2. Pertaining harmonic analysis 1. The evaluation of the har-
to whole-number multiples of the FUNDAMEN- monic content of a complex wave. See, for exam-
TAL FREQUENCY of a sound or signal, as defined ple, HARMONIC WAVE ANALYZER; SCHEDULE
harmonic analyzer See HARMONIC WAVE ANA-
Second harmonic wave LYZER, SPECTRUM ANALYZER, and WAVE ANA-
harmonic Fourth
harmonic antenna An antenna operated at a har-
wave harmonic
monic of the lowest frequency at which it is reso-

nant. For example, a half-wave dipole cut for 7.0
MHz, but used for transmitting and receiving at
21.0 MHz, is functioning at the third harmonic.
harmonic attenuation Reduction of the amplitude
of harmonic components in a complex wave using
filters, tuned amplifiers, or special modes of oper-
Fundamental wave
harmonic attenuator A circuit, device, or method
of operation (such as a filter, tuned amplifier,
special biasing, or special bypassing) for reducing
the amplitude of harmonics.
harmonic component See HARMONIC.
harmonic composition See HARMONIC DISTRI-
Fundamental pip
harmonic content The amount of harmonic
energy present in a complex wave. Also see

pip Third harmonic-cut crystal Also called overtone crystal.
harmonic Fourth A quartz crystal that, when operated in the
pip harmonic proper circuit, oscillates at a harmonic of the
(fundamental) frequency dictated by its thick-
harmonic detector A detector tuned to respond to
a harmonic of a signal.
Frequency harmonic distortion 1. The generation of har-
monics by the circuit or device by which the sig-
B nal is processed. 2. The deformation of the
original signal that results from the action de-
harmonic: waves (A) scribed in 1. 3. The disproportionate reproduc-
and spectrum-analyzer display (B) tion of a signal™s harmonic components.
harmonic distortion meter See DISTORTION ME-
harmonic accentuation Increasing the amplitude
harmonic-distortion percentage In a signal con-
of harmonic components in a complex wave using
taining harmonics, the harmonic energy as a per-
filters, amplifiers, or special modes of operation.
centage of the total signal energy (fundamental
harmonic accentuator A circuit or device, such as
plus all harmonics). Also called total harmonic
a harmonic amplifier or bandpass filter, for em-
distortion (THD).
phasizing signal harmonics.
332 harmonic distribution • hassium

harmonic distribution For a given signal, the vari- harmonic suppression See HARMONIC ELIMINA-
ous frequencies and amplitudes of its harmonics, TION.
specified within a certain range of frequencies. harmonic suppressor See HARMONIC ELIMINA-
harmonic elimination The complete removal of TOR.
one or more harmonics from a complex wave us- harmonic tolerance The harmonic content per-
ing a filter or special mode of operation. missible in a given system.
harmonic eliminator A circuit or device, such as a harmonic totalizer An instrument for measuring
band-suppression filter, for removing harmonics. total harmonic distortion. See, for example, DIS-
harmonic filter 1. A bandpass filter for transmit- TORTION METER.
ting one or more harmonics of a complex input harmonizer A circuit that changes the frequency
wave. 2. A band-suppression filter for removing of an audio signal, or produces an output at sev-
one or more harmonics of a complex input wave. eral audio frequencies from an input having only
harmonic frequency 1. In a complex wave, the one audio frequency. Used in sound recording for
frequency of a component that is a multiple of special effects.
the FUNDAMENTAL FREQUENCY by a whole- harness A tied bundle of wires or cables for wiring
number factor of two or more. 2. A frequency that electronic equipment.
is a whole-number (two or more) multiple of an- harp antenna A vertical antenna consisting of a
other frequency to which it is referred. Compare number of wires that fan out from point to point
NONHARMONIC FREQUENCY. along a horizontal supporting wire.
harmonic generator 1. An oscillator operated so hartley A unit of digital information equivalent to
that it generates strong harmonics of the funda- 3.32 bits. Used in certain computer applications.
mental frequency. 2. See FREQUENCY MULTI- Hartley oscillator A radio-frequency (RF) oscilla-
PLIER. 3. See HARMONIC AMPLIFIER. tor that uses a single inductor with a tap on the
harmonic intensification See HARMONIC AC- windings to provide the feedback. The amount of
CENTUATION. feedback is controlled by the position of the coil
harmonic intensifier See HARMONIC ACCENTU- tap. A variable capacitor in parallel with the in-
ATOR. ductor determines the oscillating frequency and
harmonic interference Interference resulting allows for frequency adjustment. The circuit uses
from the harmonics of radio or test signals. about 25 percent of its output power to produce
harmonic motion Periodic motion typified by a feedback. The other 75 percent of the power can
swinging pendulum and illustrated by the plot of be delivered to external circuits or devices. Com-
a sine wave. pare COLPITTS OSCILLATOR.
harmonic oscillator A crystal oscillator whose
output frequency is a harmonic of the crystal fre-
harmonic percentage See HARMONIC-DISTOR-
harmonic producer 1. An oscillator that uses a
tuning fork to establish the fundamental fre-
quency. The output can be an odd or even har-
monic of this frequency. 2. See FREQUENCY
MULTIPLIER. 3. A nonlinear circuit used in a cal-
ibrator to generate markers at integral multiples
of the fundamental frequency.
harmonic ratio 1. In a complex wave, the ratio of
harmonic energy to total signal energy (funda-
mental plus all harmonics). 2. In a complex wave,
the ratio of harmonic energy to fundamental- Hartley oscillator
frequency energy.
harmonic reducer See HARMONIC ATTENUATOR.
harmonic reduction See HARMONIC ATTENUA- hash 1. Electrical noise, especially wideband noise
TION. with a characteristic hissing sound in a radio re-
harmonic resonance Resonance of an antenna or ceiver. 2. Undesirable or purposefully meaningless
a circuit at a whole multiple of the applied signal information, as used in a hash total (checksum).
frequency. hash filter A radio-frequency filter for eliminating
harmonic ringing In wire telephony, the use of HASH noise in a radio receiver.
alternating-current signal harmonics for selective hassium Symbol, Hs. Also called unniloctium
ringing. (Uno). Atomic number, 108. The most common
harmonic series of tones A set of audio-frequency isotope has atomic weight 265. Classified as a
tones in which the frequencies can be specified by transition metal. It is human-made and not
f, 2f, 3f, 4f, and so on. known to occur in nature.
hat • head room

hat 1. Also called capacitance hat. A small disk or disk or diskette drive, a transducer that delivers
set of wires attached to the end(s) of an antenna and picks up recorded data.
radiator, lowering the resonant frequency and in- head alignment 1. Positioning the cone of a dy-
creasing the usable bandwidth. 2. A procedure namic speaker so that the voice coil moves freely
for randomizing data. (i.e., without rubbing against the core). 2. Posi-
hash total See CHECKSUM. tioning a magnetic-recorder head so that a proper
hatchdot pattern A television test pattern consist- relationship to the moving tape is maintained.
ing of a crosshatch pattern with dots around its head amplifier A self-contained amplifier or pre-
outer edges and one dot at its center. amplifier in the head of a microphone or sound-
hatted code A form of code in which randomiza- on-film pickup.
tion is used to maximize the difficulty of breaking head degausser A device used for the purpose of
the code. demagnetizing the head of a tape recorder. Un-
Hay bridge An alternating-current bridge for mea- wanted magnetization can build up because of
suring the inductance and Q of an inductor in direct-current components in the driving signal.
terms of resistance, frequency, and a standard head demagnetizer See HEAD DEGAUSSER.
capacitance. head end In a television network or system, the lo-
cation from which signals are sent to subscribers.
header 1. A (usually glass) disk or wafer through
which one or more leads pass and to which they
Rx are fully sealed. Can be used as the terminal base
Lx of an enclosed plug-in unit, such as a miniature
coil, filter, or similar components. Also see
GLASS-TO-METAL SEAL. 2. A data set placed be-
det fore other sets as a means of identifying them
and, possibly, including control data pertinent to
R2 the sets so identified.
R3 header capacitance Capacitance between or
Inductance among the leads in a header (see HEADER, 1).
Q Balance
balance header label A header recorded on a magnetic tape
file (see HEADER, 2).
head gap 1. In computer disk or tape drives, the
distance between the head and the magnetic
medium. 2. In audio operations, the spacing be-
tween tape-unit head electrodes; also called gap
Hay bridge
heading The direction taken by a vehicle with ref-
erence to some point (such as a radio beacon,
haywire Loose, disorderly, or apparently careless
true north, or magnetic north).
headlight In radar operations, a small rotating an-
haz Abbreviation of HAZARD.
hazard Abbreviation, haz. A dangerous or poten-
headphone A small acoustic transducer worn
tially dangerous circuit, device, material, method,
against the ear for listening to music without dis-
situation, or system (e.g., electric-shock hazard).
turbing others, or for monitoring live or recorded
H beacon A form of homing beacon with an omni-
material without being disturbed by noise in the
directional radiation pattern and a radio-
environment. Also see RECEIVER, 2.
frequency output of between 50 W and 2 kW.
headphone amplifier An audio-frequency ampli-
H bend See H-PLANE BEND.
fier designed and operated primarily to supply a
HCD Abbreviation of hard-copy device.
signal to headphones.
headphone receiver A portable radio receiver,
HDB-3 code Abbreviation of HIGH-DENSITY
usually for AM and/or FM broadcast, consisting
of a pair of headphones or a headset with the ra-
dio built into it.
head room 1. In a high-fidelity sound system, the
extent, measured in decibels, to which an ampli-
fier can be operated beyond the zero point on its
H-display See H-SCAN.
volume-unit (VU) meter without causing objec-
He Symbol for HELIUM.
tionable distortion on sound peaks. 2. In tape
head 1. The top or operating portion of a device
recording, the region between the maximum
(e.g., microphone head or dynamic-speaker
recording level specified by the manufacturer of
head). 2. In magnetic recording and reproduc-
the equipment, and the amplitude at which tape
tion, the magnetic device (transducer) that deliv-
overload occurs. It is specified in decibels.
ers or picks up recorded impulses. 3. In a hard
334 headset • heat therapy

headset An assembly consisting of one or two ear- heater 1. The filament of an indirectly heated vac-
phones, a headband, and a flexible cord. Also see uum tube. 2. The filament in an indirectly heated
HEADPHONE and RECEIVER, 2. thermistor.
head stack In magnetic recording, an assembly of heater-voltage coefficient The amount of fre-
two or more heads for multitrack service. Also see quency change per volt of fluctuation in the fila-
HEAD, 2. ment voltage of a Klystron.
head station See BASE STATION. heat exchanger A device or system that removes
head-to-tape contact In magnetic-tape recording heat from a hot body and transfers it to another
or playback, physical contact between the tape body or to the surrounding air.
and the head. heat-eye tube An infrared-sensitive device used
hearing aid A miniature audio-frequency device for the purpose of locating objects in visible dark-
that amplifies sound for people with impaired ness. The tube consists of a cathode-ray device
hearing. It consists of a microphone, a high-gain that is sensitive to infrared radiation.
amplifier, and an earphone or bone-conduction heat gradient The temperature difference between
transducer. two points on a body, divided by the distance be-
hearing-aid battery A physically small battery de- tween the two points.
signed for use with hearing aids. Such a battery heating depth See DEPTH OF HEATING.
is usually of the lithium type, or some other type heating effect The production of heat (power loss)
that has long life under conditions of low current by electric current flowing in a conductor.
drain. heating element 1. See HEATER. 2. The resis-
hearing loss A measure of hearing impairment. tance element (such as a strip or coil) that gener-
Generally expressed as the ratio, in decibels, of ates heat in an electric-heating device.
an individual™s threshold of hearing to the normal heat loss 1. Heat emitted by conduction, convec-
threshold of hearing. Also see AUDIOLOGIST, tion, or radiation from a body at a relatively high
AUDIOMETER, and AUDIOMETRIST. temperature. 2. Power loss as a result of the heat-
heart fibrillation A condition in which the heart ing effect of an electric current.
muscle twitches at random, rather than pumping heat of fusion The amount of heat required to melt
blood normally. This can be caused by an electric a unit mass of a solid that has reached its melt-
shock through the heart of 100 mA to 300 mA. If ing point.
normal heart function is not restored, death will heat of radioactivity Heat generated during the
follow. process of radioactive disintegration.
heart pattern See CARDIOID PATTERN. heat of reaction In a chemical or electrochemical
heart telemetry See ECG TELEMETRY. reaction, the heat (in calories) absorbed or re-
heat A form of energy transferred by conduction, leased.
convection, or radiation between two bodies hav- heat of vaporization The amount of heat required
ing different temperatures. The amount of heat is to convert 1 gram of a liquid to a vapor without
expressed in degrees, British thermal units, calo- raising its temperature.
ries, joules, or kelvins. heat radiator See HEATSINK.
heat aging 1. The degeneration of a substance, ag- heat rays See INFRARED RAYS.
gravated by high temperatures. 2. A test that heat remover 1. See HEATSINK. 2. A forced-air or
indicates the immunity of a substance to forced-liquid cooling system.
degeneration because of high temperatures. heat-resistant glass See PYREX.
heat coil A device that disconnects a circuit when heat-sensitive resistor See THERMISTOR.
the temperature reaches a certain minimum heat-sensitive switch A make-and-break device,
level. such as a thermostat, that is actuated by a
heat detector A sensor of heat. See, for example, change in temperature.
BOLOMETER, INFRARED DETECTOR, MICRO- heat-shrink tubing An insulated flexible sleeving
RADIOMETER, RADIOMETER, THERMISTOR, made from a plastic that shrinks permanently for
THERMOCOUPLE, and THERMOPILE. a tight fit when heated; it is commonly used at the
heated-pen recorder See THERMAL RECORDER. joint between a cable and connector.
heated-stylus recorder See THERMAL RE- heatsink A heat exchanger in the form of a heavy,
CORDER. metallic mounting base or a set of radiating fins.
heated-wire flowmeter See HOT-WIRE FLOWME- It conducts heat away from such devices as
TER. power transistors, heavy-duty resistors, or power
heated-wire sensor A hot wire used to discrimi- tubes, and dissipates the heat into the surround-
nate between substances, according to how they ing environment via convection and radiation.
affect its heating. See, for example, GAS DETEC- heatsink resistance The opposition offered by a
TOR (also usable as a vacuum gauge), HOT-WIRE heatsink to the flow of heat.
ANEMOMETER, and HOT-WIRE MICROPHONE. heat therapy 1. The use of radio-frequency heating
heat engine A machine that converts heat energy for therapeutic purposes. Also see DIATHERMY. 2.
into mechanical energy. The use of infrared rays for therapeutic purposes.
heat transfer • helical antenna

hectowatt Abbreviation, hW. A unit of power equal
to 100 watts. Seldom used; power in this range is
usually expressed in terms of the WATT or the
heelpiece A part of an electronic relay that pro-
vides mechanical support for the armature.
Hefner candle A unit of luminous intensity equal
to 0.9 candela; the standard (German) is the
Hefner lamp A standard light source whose lumi-
nous intensity is 0.9 candela. It burns amyl ac-
etate (banana oil) and its flame has been the
standard of the HEFNER CANDLE, a unit of lu-
minous intensity devised in Germany. Also see
height control In a television receiver circuit, the
Heatsink potentiometer or rheostat that controls the verti-
cal dimension of the picture by varying the ampli-
tude of vertical scanning pulses.
height finder An altitude-measuring radar sys-
height-position indicator Abbreviation, HPI. A
radar displaying the height of a target, its angular
elevation, and the slant range.
Heil oscillator An oscillator based on a special
tube consisting of a heated cathode, first anode,
metal cylinder, and second anode. Electrons
emitted by the cathode pass through a hole in the
first anode and become a beam, which passes
heat transfer The movement of heat from one
through the cylinder and strikes the second an-
point to another by absorption, conduction, con-
ode (collector). Electron bunching in the cylinder
vection, or radiation.
causes energy to be transferred to a tank circuit
heatronic Pertaining to the heating of a dielectric
between the cylinder and anodes.
material subjected to a high voltage.
heat unit 1. See BRITISH THERMAL UNIT. 2. See
heat waves See INFRARED RAYS.
Anode 1 beam
heat writer See THERMAL RECORDER. Anode 2
Heaviside-Campbell bridge A form of mutual-
inductance bridge. Mutual inductance is deter- Cathode
mined without regard to the operating frequency.
Heaviside layer See KENNELLY-HEAVISIDE
heavy hydrogen An isotope of hydrogen. The term ’
is applied to deuterium, whose nucleus consists dc Input
of one proton and one neutron, and also to tri-
RF output
tium, whose nucleus consists of one proton and
two neutrons.
heavy metal A metal having a specific gravity of
5.0 or higher. Examples: iron (7.85 to 7.88), lead
(11.3), nickel (8.6 to 8.9), mercury (13.6), plat- Heil oscillator
inum (21.4).
heavy water Formula, D2O. Water in which deu-
Heisenberg uncertainty principle See UNCER-
terium (HEAVY HYDROGEN), rather than ordi-
nary hydrogen has combined with oxygen.
hekto- See HECTO-.
hecto- Abbreviation, h. A prefix meaning hun-
dred(s), (i.e., 102). heliacal cycle See SUNSPOT CYCLE.
helical antenna A spring-shaped antenna mounted
hectometric wave An electromagnetic field whose
perpendicular to a flat metal-plate reflector, an ar-
wavelength is on the order of hundreds of meters
rangement that produces circularly polarized
(i.e., at least 100 meters, but less than 1000 me-
waves in a narrow beam. It is used primarily at
ters). The frequency ranges from 300 kHz to 3
ultra-high and microwave radio frequencies.
336 helical-beam antenna • Herschel-Quincke tube

helical-beam antenna See HELICAL ANTENNA. helix recorder An information recorder using a
helical line The helix in a backward-wave oscilla- spiral method of scanning. The recording
tor or traveling-wave tube. medium is usually drum-shaped.
helical potentiometer A potentiometer whose re- Helmholtz coil A device consisting of two crossed-
sistance element is a wire wound into a coil of field primary windings in which an inductively
several turns. The slider moves over the wire (or coupled secondary winding rotates. The primary
the larger coil) from one end to the other as the windings carry currents that differ in phase by 90
slider or coil is turned through several complete degrees. Rotating the secondary coil provides 360
revolutions. Also called MULTITURN POTEN- degrees of continuously variable phase shift.
helical scanning Radar scanning by an antenna
that moves vertically as it moves horizontally,
producing a spiral motion to the radiated beam. Output
helical sweep See SPIRAL SWEEP, 1, 2.
helical transmission line See HELICAL LINE.
2 H
helicone An antenna used at ultra-high and mi- Input 2
crowave frequencies, consisting of a helical radia-
tor within a cone-shaped reflector.

Feed point
Helmholtz coil

Helmholtz double layer An intermolecular layer
between a metal and an electrolyte in which it is
immersed. It is formed when the adhesive force be-
tween the metal and electrolyte decreases the sur-
face tension of the metal, causing positive ions to
migrate from the metal into the liquid. The metal,

charged negatively, and the electrolyte, charged
positively, form a capacitor whose dielectric is the
Helmholtz layer.
Helmholtz resonator An acoustic (sound) cham-
ber whose geometry, in combination with the size
of a small opening, results in resonance at a spe-
cific frequency.
HEM Abbreviation of hybrid electromagnetic (see, for
helionics The science of converting solar heat into
hemimorphic Pertaining to an object with ends
electrical energy. The term is an acronym from
that have unlike faces.
helio- (pertaining to the sun) and electronics.
heliostat 1. A servo-controlled motor-driven de-
henry Symbol, H. The standard unit of inductance.
vice that drives a mirror to keep sunlight
It is the inductance exhibited by a closed circuit
trained upon a specific target. 2. By extension,
in which one volt is produced by a current chang-
any similar device to keep a solar cell pointed to
ing uniformly at one ampere per second. This is a
the sun.
large unit of inductance; more common units are
helitron A form of oscillator used at ultra-high and
microwave frequencies. The output frequency is
hermaphroditic plug A plug that has the prongs of
variable over a wide range.
a male plug and the recessed contacts of a female
helium Symbol, He. A gaseous element. Atomic
plug. Compare FEMALE PLUG and MALE PLUG.
number, 2. Atomic weight, 4.0026.
hermetically sealed Constructed in manufacture
helium group The six inert gases in group 0 of the
so as to be permanently closed against the entry
periodic table: argon, helium, krypton, neon,
of air or other gases, dust, and moisture.
xenon, and radon.
hermetic seal A permanent, air-tight seal that ef-
helium-neon laser A laser in which the lasing sub-
fectively prevents corrosion from elements in the
stance is a mixture of helium and neon. Produces
outside environment.
a characteristic brilliant red visible output. Also
herringbone pattern A pattern of interference in a
see HELIUM and NEON.
television picture, so named because of its resem-
helix 1. A single-layer coil. 2. That which is coil-
blance to the skeleton of a fish.
shaped (i.e., spiral in configuration). 3. See HELI-
Herschel-Quincke tube An acoustic device that
demonstrates sound interference. The device has
helix line See HELICAL LINE.

Herschel-Quincke tube • heterodyne wave analyzer

two hollow cylinders, one of which can be ad- heterodyne 1. To beat one alternating-current sig-
justed in length. At the far end of the apparatus, nal against another to produce one or more beat-
the cylinders are joined together. The resultant frequency signals. Also see BEAT FREQUENCY
amplitude depends on the difference in length be- and BEAT NOTE. 2. The whistle produced when
tween the cylinders. Sound wavelengths can be two signals very close in frequency are mixed in a
measured using this apparatus. radio receiver. 3. To combine radio signals in a
hertz Abbreviation, Hz. The standard unit of fre- mixer, the purpose of which is to produce a sum
quency (of periodic phenomena, such as alternat- or difference signal for further processing.
ing or pulsating currents); 1 Hz = 1 cycle per heterodyne detection 1. Signal detection by beat-
second. One Hz is an extremely small unit of fre- ing the incoming signal against one produced by
quency; more common units are the KILOHERTZ, a local oscillator. In this way, an unmodulated
the MEGAHERTZ, and the GIGAHERTZ. signal is made audible (the beat note is an audio
Hertz antenna An ungrounded halfwave antenna frequency). 2. Signal detection by a superhetero-
fed by a transmission line attached to one end or dyne circuit.
to the center of the radiator. See, for example, heterodyne detector 1. A detector that makes a
CENTER-FED ANTENNA and END-FED AN- radio-frequency (RF) signal audible by beating it
TENNA. Compare MARCONI ANTENNA. against the RF signal of a local oscillator, the
Hertz effect Ionization of a gas, produced by in- product being an audio-frequency (AF) beat note.
tense ultraviolet radiation. 2. The FIRST DETECTOR or SECOND DETEC-
Hertzian oscillator See HERTZ OSCILLATOR. combination linear detector and local RF oscilla-
Hertzian radiation Radiation of electromagnetic tor used to detect and measure the frequency
(radio) waves. of test signals. Also see HETERODYNE FRE-
Hertzian waves Electromagnetic waves in the ra- QUENCY METER.
dio spectrum, with wavelengths longer than those heterodyne eliminator See WHISTLE FILTER.
of infrared, visible light, ultraviolet, X rays, or heterodyne filter See WHISTLE FILTER.
gamma rays. heterodyne frequency The frequency of the signal
Hertz oscillator A damped-wave generator of os- obtained by beating one signal against another.
cillations, used by Hertz in his demonstration of heterodyne frequency meter A frequency-
radio waves in 1888 (verifying the earlier predic- measuring device that contains a variable-
tion by James Clerk Maxwell). The oscillator con- frequency oscillator (VFO), a mixer, and an
tains a spark gap supplied by an induction coil, indicator such as an analog meter. The oscillator
attendant coils, capacitors (in the prototype, Ley- frequency is adjusted until zero beat is reached
den jars), and two large metal plates. with the signal source. This condition is shown by
a dip in the meter indication. An audio amplifier
can be coupled to the output of the device instead
of a meter; in this case the heterodyne appears as
Spark gap
Metal Metal an audible tone whose frequency drops to zero
plate plate when the oscillator frequency is equal to the
signal frequency being measured.
heterodyne method See HETERODYNE, 1.
heterodyne oscillator A signal generator whose
output is the beat product of outputs from two in-
ternal oscillators. The output frequency can be ei-
ther the sum or the difference of the oscillator
frequencies, as selected by output filtering or
From secondary
of induction coil
heterodyne reception Radio reception (especially
in telegraphy) by means of the beat-note process.
Hertz oscillator
heterodyne repeater A REPEATER in which the
Hertz vector A single vector that specifies the elec-
received signals are converted to another fre-
tromagnetic field (electric and magnetic compo-
quency before transmission.
nents) of a radio wave.
heterodyne-type frequency meter See HETERO-
hesitation As distinct from a halt, a brief break in
a computer program run during which internal
heterodyne wave analyzer A type of audio-
operations are occurring, such as data transfer to
frequency (AF) wave analyzer. The input signal is
a peripheral.
heterodyned in a balanced modulator with the
heterochromatic Consisting of different frequen-
signal from an internal tunable oscillator. One of
cies, wavelengths, or colors. Compare MONO-
the resulting sidebands is passed through a
338 heterodyne wave analyzer • high-efficiency linear amplifier

sharp bandpass filter, whose output actuates an that prevents unauthorized use of a computer,
alternating-current (ac) voltmeter. The internal network, or database. The password levels allow
oscillator is tuned slowly so that different compo- users various degrees of control over the host ma-
nents of the balanced-modulator output side- chine.
band pass successively through the filter. The hi-fi 1. Contraction of HIGH-FIDELITY. 2. In video
amplitude-versus-frequency function of the input recording, the addition of sound having high fi-
signal is determined by noting the meter readings delity.
as the internal oscillator is tuned. high 1. Pertaining to a circuit point or condition at
heterodyne wavemeter See HETERODYNE FRE- some potential above ground. 2. The logical digit
QUENCY METER. 1. 3. The condition of having relatively large mag-
heterodyne whistle See HETERODYNE, 2. nitude (e.g., HIGH FREQUENCY and HIGH VOLT-
heterogeneous Pertaining to a group of objects or AGE). 4. Pertaining to the upper portion of a
devices that have differing characteristics. range, as in HIGH BAND or HIGH FREQUENCY.
heterogeneous radiation Any broadband form of 5. Characterized by greater-than-normal re-
radiation. In particular, broadbanded radio sponse or performance, as in HIGH Q or HIGH FI-
waves, infrared radiation, visible light, ultraviolet, DELITY.
X rays, or gamma rays. high band 1. The higher or highest frequency band
heterolysis The HYDROLYSIS of a compound into used in communications, testing, or processing,
two oppositely charged ions. when several bands are available. 2. The very-
heteropolar generator An electric generator in high-frequency (VHF) television channels 7
which the active conductors move through mag- through 13. 3. The communications frequency
netic fields, first in one direction, then in the range from about 144 MHz to about 170 MHz.
other direction. This is done by means of rotation high boost In sound recording and reproduction,
in a nonuniform magnetic field. Most generators the emphasis of high frequencies in an operating
in common use are of this kind. spectrum. Also called HIGH-FREQUENCY COM-
heuristic knowledge In artificial intelligence (AI), a PENSATION.
form of machine knowledge in which a computer high-C circuit A tuned circuit having high capaci-
learns from its mistakes. As a complex program is tance and low inductance at a given frequency.
repeatedly run over a period of time, the number Such a circuit is characterized by high selectivity
of errors per run approaches zero. and low voltage. Compare HIGH-L CIRCUIT. Also
heuristic program In artificial intelligence (AI), a see LC RATIO.
program with which the computer solves a prob- high contrast In an image, a limited range of gray
lem by trial and error, often learning in the pro- values between black and white, or a similar con-
cess so that mistakes will not be repeated on dition in a color image (overbright whites, little
subsequent runs. shadow detail). Also see CONTRAST.
Heusler™s alloys Ferromagnetic alloys that contain high definition In facsimile or television, a condi-
one or more non-magnetic metals (such as alu- tion of minute detail so that the original scene is
minum, copper, or manganese). faithfully reproduced.
hexadecimal number system An alphanumeric, high-definition television Abbreviation, HDTV. A
base-16 system of number notation used in some method of getting enhanced detail into a televi-
computers. The system uses the usual digits plus sion (TV) picture and for obtaining better audio
the letters A through F to represent the numbers quality, compared with standard analog TV.
10 through 15 (each place can only hold one sym- There are several different schemes. The most no-
bol). ticeable feature is the crispness of the picture.
hex inverter A collection of six digital inverters, or This is vividly apparent in big-screen installa-
NOT gates, contained within one package, usu- tions, which have traditionally suffered from im-
ally an integrated circuit. age blurring. A standard TV picture has 525 lines
Hf Symbol for HAFNIUM. per frame, but HDTV systems can have more
HF Abbreviation of HIGH FREQUENCY. than twice that number. Another important dif-
Hg Symbol for MERCURY. ference is that HDTV is digital; this minimizes
HH beacon In radionavigation, a nondirectional susceptibility to interference. Interlacing is used
homing beacon. in some systems.
hi 1. Contraction of HIGH. 2. Radiotelegraph sym- high-density bipolar-3 code A communications or
bol for a laugh, often verbalized by radio ama- digital code in which two logic highs (ones) can
teurs. occur in sequence, without the need for an inter-
HIC Abbreviation of HYBRID INTEGRATED CIR- vening logic low (zero) to separate them.
CUIT. high-efficiency linear amplifier A LINEAR AM-
HIDM Abbreviation of HIGH-INFORMATION PLIFIER with higher operating efficiency than is
DELTA MODULATION. obtainable with conventional class-B linear am-
hierarchical password protection Also called plifiers. Efficiencies on the order of 60% at 100%
multilevel password protection. A security feature modulation are possible.
high-energy materials • high order

high-energy materials See HARD MAGNETIC MA- Such a circuit is characterized by low selectivity
TERIALS. and high voltage. Compare HIGH-C CIRCUIT.
high-energy particle 1. A SUBATOMIC PARTICLE Also see LC RATIO.
that has been given high velocity by a particle ac- high-level audio signal An audio-frequency signal
celerator. 2. High-speed subatomic particles that has been preamplified (e.g., the output of a
emitted by the sun during a solar flare, or arriv- compact-disc player). Compare LOW-LEVEL AU-
ing from outer space. DIO SIGNAL.
high-energy physics The discipline dealing with high-level input current 1. Pertaining to the test-
the characteristics, properties, and applications ing of intertransistor leakage in an integrated cir-
of HIGH-ENERGY PARTICLES. cuit (IC) having multiple emitter inputs. 2. The
higher-order language See HIGH-LEVEL LAN- current into an IC input at minimum high-level
GUAGE. voltage.
high fidelity Abbreviation, hi-fi. Pertaining to an high-level language Also called higher-order lan-
audio-frequency system that is very faithful to guage. A computer programming language in
the signal it is processing (i.e., one characterized which the operator is easily able to communicate
by extremely low distortion and wide frequency with the machine. It generally serves as an inter-
response). face between a human programmer and the MA-
high frequency Abbreviation, HF. Pertaining to CHINE LANGUAGE. Examples are BASIC, C,
frequencies in the 3- to 30-MHz band (wave- C++, COBOL, and FORTRAN.
lengths from 10 to 100 meters). Also see RADIO high-level modulation In an amplitude-modula-
SPECTRUM. ted transmitter, introduction of the audio at the
high-frequency alternator A dynamo for generat- final stage of radio-frequency amplification, per-
ing radio-frequency energy. mitting 100% modulation of the full-power signal.
high-frequency bias In a tape recorder, a high-
frequency sinusoidal signal superimposed on the
signal being recorded, for improving linearity and
dynamic range.
high-frequency compensation See HIGH BOOST.
high-frequency converter See SHORTWAVE
Osc Amp
high-frequency crystal See HARMONIC CRYS-
high-frequency direction finder Abbreviation,
HDF. A direction finder operated at high radio fre-
quencies (i.e., between about 3 MHz and 30 MHz).
high-frequency heating Electronic heating of ma- Audio
terials by high-frequency energy. See, for exam- Audio power
high-frequency resistance See RADIO-FRE-
QUENCY RESISTANCE. high-level modulation
high-frequency speaker See TWEETER.
high-frequency trimmer 1. In older high-
frequency communications receivers, a low-value high-level output current 1. Pertaining to the
variable capacitor operated in parallel with a usu- testing of drive capability and fanout of an inte-
ally front-panel tuning capacitor to set the high- grated circuit (IC). 2. The current flowing from an
frequency end of the tuning range. See, for IC output when in the high state.
example, OSCILLATOR TRIMMER. 2. A small high-level recovery Hardware recovery using data
variable capacitor used in conjunction with a not involved in the failure, such as that on a mag-
larger tuning capacitor, the function of which is netic storage medium. Also see HARDWARE RE-
to permit precision tuning of the larger device. COVERY.
high-impedance-state output current Pertaining highlight 1. A bright area in a television picture. 2.
to tests that ensure that an integrated circuit will In computer data processing, the defining or set-
not overload a bus line. ting-off of a block of data (such as text), with the
high-impedance voltmeter A voltmeter having an intention of relocating, editing, or deleting it.
input impedance of at least several megohms. high-noise-immunity logic Abbreviation, HNIL. A
high-information delta modulation A com- form of bipolar digital logic designed for minimal
panded form of delta modulation, operating at sensitivity to noise. Also known as high-threshold
comparatively low sample rate. logic (HTL).
high-L circuit A tuned circuit having high induc- high order Descriptive of the relationship between
tance and low capacitance at a given frequency. bits or digits in a word or number. Of two digits,
340 high order • hiss

the one holding the higher place value is the high- high-resistance voltmeter A voltmeter having an
order digit (e.g., 2 is the high-order digit in 25). input resistance of at least several megohms.
high-pass filter A combination of capacitance, in- high-speed carry In computer operation, a carry
ductance, and/or resistance, intended to produce into a column causing a carry out, circumventing
large amounts of attenuation below a certain fre- the usual intermediate adding circuit.
quency and little or no attenuation above that fre- high-speed diode See COMPUTER DIODE.
quency. The frequency at which the transition high-speed flip-flop A flip-flop having short
occurs is called cutoff. At cutoff, the power atten- switch-on and switch-off time.
uation is 3 dB with respect to the minimum at- high-speed oscilloscope An oscilloscope with excel-
tenuation. At frequencies above cutoff, the power lent high-frequency and unit-function response. It
attenuation is less than 3 dB. At frequencies be- can reproduce high-speed pulses faithfully.
low cutoff, the power attenuation is more than high-speed relay A relay with a short make or
3 dB. The simplest circuit consists of a parallel short break interval.
inductor or a series capacitor. The inductance- high-speed transistor See SWITCHING TRANSIS-
capacitance (LC) circuit has a combination of par- TOR.
allel inductors and series capacitors. In the high tension Pertaining to utility power-transmis-
resistance-capacitance (RC) circuit, resistors are sion lines on which there are very high voltages,
substituted for the inductors. Compare BAND- typically 100 kilovolts (100 kV) or more.
PASS FILTER, BAND-REJECTION FILTER, LOW- high-tension line A power-transmission line car-
PASS FILTER. rying a very high voltage. It is generally used for
the transfer of electric power over long distances.
high-threshold logic See HIGH-NOISE-IMMUNITY
high voltage 1. A voltage considerably higher than
those ordinarily encountered in a particular ap-
In Out
plication. The term is comparative; a few hundred
L L L volts might be considered high in one situation,
but low in another. 2. In a cathode-ray tube, the
voltage that accelerates the beam electrons. 3. In
a television receiver, the picture-tube anode volt-
age. 4. In a vacuum-tube power amplifier, the
plate supply voltage.
high-pass filter high-voltage probe A very-high-resistance probe
for measuring high voltages with a low-range
high-pass-filter method A method of measuring
highway A path over which multiple signals are
the total harmonic distortion (THD) percentage
propagated using time-division multiplexing.
using a high-pass filter to separate the harmonics
HILAC Acronym for heavy-ion linear accelerator.
from the fundamental. The output voltage Vo of
hill-and-dale recording See VERTICAL RECORD-
the filter is compared with the input voltage Vi;
then THD = 100Vo/Vi.
hinged-iron instrument An alternating-current
high-performance Pertaining to apparatus designed
meter whose input transformer core is hinged in
for continuous operation with maximum reliability.
two parts. By means of a thumb trigger, the core
high-performance navigation system Acronym
can be opened, then closed around the current-
HIPERNAS. An electromechanical guidance sys-
carrying conductor that induces magnetism in the
tem that is purely inertial and self-compensating.
core; a secondary coil delivers current to the me-
high-potential test A high-voltage test of insula-
ter. Also called clamp ammeter or clamp voltmeter.
tion, in which the applied voltage is continuously
increased until the breakdown point of the dielec-
tric is reached.
hipernick A high-permeability alloy of iron and
high-power rectifier A rectifier designed for high-
voltage, high-current operation.
hipot Contraction of high potential. See HIGH-
high Q For a component or circuit, a high value for
the ratio X/R (reactance to resistance). This is a
hiss 1. A high-pitched sound rich in sibilants (s,
relative term because a particular numerical
sh, and z sounds) produced by random high-
value of Q, considered high in one situation,
frequency fluctuations in current. 2. The character-
might be regarded as low under other circum-
istic, high-pitched background noise (as in 1)
stances. Also see FIGURE OF MERIT.
accompanying super-regeneration. 3. Internally
high-resistance joint In the wiring of electronic
generated noise in a communications receiver,
equipment, a joint or connection between con-
amplified by the audio-frequency stages and ap-
ductors that is poorly made, thereby introducing
pearing at the speaker or headphones.
a high resistance between the parts.
hiss filter • hole injector

hold current Symbol, Ih. The minimum current
hiss filter See HASH FILTER.
that will keep a normally open relay closed or a
hit 1. The occurrence of a lightning stroke at a spe-
normally closed relay open.
cific point on the ground. Also called direct hit. 2.
hold electrode In a mercury switch, the electrode
The coincidence of two pulses.
that is in permanent contact with the mercury.
H lines Magnetic lines of flux.
holding beam In an electrostatic cathode-ray stor-
age tube, the electron beam that generates re-
H network A network of five impedances: two con-
placement charges for those that were stored on
nected in series between the upper input and
the dielectric surface and then lost.
output terminals, two between the lower input
holding circuit In an electromechanical relay, a
and output terminals, and one shunted between
separate circuit that, when energized, keeps the
the junctions of the series-connected im-
relay actuated.
pedances. Also called H pad, balanced tee net-
holding coil In an electromechanical relay, the ex-
work, and balanced tee pad.
tra coil that is associated with the holding circuit.
holding current 1. Current in the holding coil of a
relay. 2. In a gas tube, the minimum current re-
quired to maintain ionization.
holding gun In an electrostatic cathode-ray stor-
age tube, the electron gun that generates the
holding beam.
In Out hold mode A condition in which the output state of
a digital-logic circuit remains unchanged while
the input signals are removed.
hold-off voltage The highest voltage that can be
applied to a flashtube without causing it to fire.
holdover The flow of current through the ionized
path created by an electric arc.
hold time 1. The time permitted for a weld to
H network
harden in resistance welding. 2. In digital com-
munications, the time for which a signal is main-
tained at a certain input after changing state at
Ho Symbol for HOLMIUM.
another specified input.
hobby robot A robot intended for amusement and,
hole 1. In a semiconductor atom, the vacancy re-
sometimes, for education. Such robots often take
sulting from the loss of an electron. When an
humanoid form. Some are programmable, and
electron is lost, so is its negative charge, leaving
can give demonstrations, play musical instru-
an equivalent net positive charge. This charge,
ments, and do other complex routines.
like that of an electron, can move as a current
hockey-stick lead On a capacitor, resistor, or
carrier. 2. The punched-out portion of a chassis
other component, a pigtail lead that is given a
or panel, through which wires can be passed or
single crimp for easy insertion into a printed-
components mounted.
circuit board.
hole conduction In a semiconductor material,
hodoscope An instrument consisting essentially of
electrical conduction as a result of HOLE CUR-
closely spaced ion counters, for studying the path
of an ionizing particle.
hole current In a semiconductor material, the
Hoffmann electrometer See BINANT ELECTRO-
electrical current resulting from the movement
of positive charge carriers (holes). Also see
hog horn A form of horn antenna used in mi-
crowave applications. It is generally used in the
hole density The degree of concentration of holes
feed system of a dish antenna. The horn opening
in a semiconductor. Also see HOLE.
points in the direction of the feed waveguide.
hole-electron pair In a semiconductor, a hole and
hold 1. To retain data in a storage device after the
a related electron. Each electron in the conduc-
data has been duplicated in another location or
tion band has a counterpart in the valence band,
device. 2. A momentary halt of an operation or
a vacancy (HOLE) left by the movement of the
process. 3. In a television receiver, a control that
electron to the conduction band.
stabilizes the vertical or horizontal synchroniza-
hole injection The creation of mobile holes in a
semiconductor by applying an electric charge.
hold circuit 1. See HOLDING CIRCUIT. 2. In a
Also see HOLE.
television receiver, the circuit associated with the
hole injector 1. The emitter electrode of a bipolar
hold control(s). Also see HORIZONTAL-HOLD
pnp transistor. 2. The metal whisker of a point-
contact diode having an n-type wafer. 3. The
player of a forward-biased junction diode.
342 hole mobility • horizon

hole mobility The ease with which a hole moves homogous field A field whose lines of flux in one
within a semiconductor. Also see CARRIER MO- plane pass through a single point.
BILITY. homolysis The decomposition of a compound into
hole storage See CARRIER STORAGE. a pair of neutral atoms or radicals.
hole storage factor In a bipolar transistor biased homomorphism A one-to-one correspondence be-
to saturation, the amount of storage charge tween the elements of two sets.
caused by excess base current. homopolar Pertaining to the union of atoms of the
hole trap In a semiconductor, an impurity that can same polarity; nonionic.
cancel holes by releasing electrons to fill them. homopolar generator A direct-current (dc) genera-
hollow coil A coreless inductor. tor whose poles have the same polarity, with re-
hollow conductor Tubing used as a low-loss con- spect to the armature. Thus, no commutator is
ductor at radio frequencies. necessary.
hollow core A core that is not solid throughout” homopolar magnet A magnet whose pole pieces
especially one that has a central mounting hole. are concentric.
holmium Symbol, Ho. A metallic element of the homunculus In artificial intelligence (AI), a com-
rare-earth group. Atomic number, 67. Atomic puter or robot that exhibits characteristics of a
weight, 164.93. Forms highly magnetic com- living being; especially, an ANDROID.
pounds. honeycomb coil A multilayer coil having a UNI-
holocamera A camera for making holograms. Also VERSAL WINDING.
see HOLOGRAM, 1 and HOLOGRAPHY. honeycomb winding See UNIVERSAL WINDING.
hologram 1. A wavefront recording made on pho- honker Also called midrange speaker. A loud-
tographic film by the process of HOLOGRAPHY. speaker that favors the middle audio frequencies.
By changing the frequency of the light transmit- Compare TWEETER and WOOFER.
ted, various magnifications of the image can be hood A light shield for a cathode-ray tube; it allows
obtained. Produces a true three-dimensional im- the screen to be viewed with a minimum of inter-
age. 2. A visible, three-dimensional display pro- ference from room light.
jected in the air or underwater by means of Hooke™s law Strain is proportional to the stress
lasers. They are often used at outdoor music con- that produces it, as long as the ELASTIC LIMIT is
certs and other events. not exceeded.
holography A method of producing a wavefront hook switch A switch that closes a circuit when a
recording of an object illuminated by laser light. headset or handset is lifted from the resting posi-
The result, an interference pattern, appears tion. The common telephone receiver uses such a
meaningless when viewed in ordinary diffuse switch.
light. But when a point source of illumination is hook transistor A four-layer pnpn semiconduc-
used, especially a laser, an image appears that is tor device, in which the outer p and n layers
convincingly three-dimensional. serve as emitter and collector, the inner n layer
homeostasis The condition of being in static equi- being the base. This places a p layer between
librium. the base and collector, resulting in a transistor
home station See BASE STATION. that provides high alpha as a result of carrier
homing 1. Guidance by means of an electronic multiplication by the additional junction in the
beacon. The vehicle maintains a course toward collector layer.
the beacon. 2. Guidance by means of some form hookup See SCHEMATIC DIAGRAM.
of emission from a target object. The emission hookup wire Flexible, insulated wire used in the
can be acoustic or electromagnetic energy. wiring of some electrical and electronic devices.
homing antenna A direction-finding antenna” hoop antenna See CAGE ANTENNA.
especially one on a mobile vehicle. hoot stop During a computer program run, a loop
homing beacon A station radiating a beam for use made evident by a sound signal.
in direction finding by mobile vehicles. hop In long-distance radio communications, the
homing device A receiving device mounted on a transmission of a wave and its subsequent return
mobile vehicle, and that continuously indicates to the earth from the ionosphere; it is of impor-
the direction of a selected transmitting station tance mainly at low, medium, and high frequen-
that is the vehicle™s destination. cies.
homing relay A stepping relay that returns to its hor Abbreviation of HORIZONTAL. (Also, H and
starting position after each switching sequence. horiz.)
Also see STEPPING SWITCH. horiz Occasional abbreviation of HORIZONTAL.
homing station See HOMING BEACON. The usual form is hor; another alternate is H.
homodyne reception See ZERO-BEAT RECEP- horizon 1. For a specific location, the circle on the
TION. celestial sphere midway between the zenith (the
homogeneous 1. Uniform in structure; similar at point directly overhead) and the nadir (the point
all points or locations. 2. Consisting of many directly underfoot). 2. Also called visual horizon.
identical elements. The set of points, as viewed from a particular
horizon • horizontal flowcharting

location, where the sky and the earth appear to Beamwidth
meet (i.e., the last visible part of the earth™s sur- 0°
face from a given observation point). 3. Also
called radio horizon. The set of points, from a par-
ticular location at a given radio frequency, repre-
senting the maximum communications range via
the ground wave under normal conditions. Also
horizontal 1. Pertaining to objects or effects in a
270° 90°
plane perpendicular to a line connecting the
zenith (the point directly overhead) and the nadir
(the point directly underfoot). 2. Pertaining to
that which is parallel to an assumed flat surface.
3. Pertaining to width deflection on a cathode-ray
horizontal AFC In a television receiver circuit, au-
tomatic frequency control (AFC) of the horizontal
sweep. It keeps the receiver™s horizontal scanning 180°
in step with that of the camera at the transmit-
ting station. horizontal beamwidth
horizontal amplification Gain provided by the
horizontal channel of a device, such as an oscil-
loscope, cathode-ray electrocardiograph, or horizontal-convergence control In a color televi-
television receiver. Compare VERTICAL sion receiver, the variable component for adjust-
AMPLIFICATION. ing the horizontal dynamic convergence voltage.
horizontal amplifier A circuit or device that pro- horizontal coordinates See CARTESIAN COORDI-
VERTICAL AMPLIFIER. horizontal deflection In a cathode-ray tube, the
horizontal angle of radiation For an antenna, the lateral movement of the electron beam on the
direction of maximum radiation in the horizontal screen. Compare VERTICAL DEFLECTION.
plane (see HORIZONTAL, 1), provided as an az- horizontal deflection coils The pair of coils that
imuth angle measured clockwise from geographic produces the magnetic field to horizontally deflect
north. the electron beam in an electromagnetic cathode-
horizontal angle of deviation In a communica- ray tube. Also see DEFLECTION COIL.
tions circuit, the angular difference, in degrees, horizontal-deflection electrodes See HORIZON-
between the compass direction from which a re- TAL DEFLECTION COILS and HORIZONTAL DE-
ceived signal arrives, and the great-circle path FLECTION PLATES.
connecting the receiving station with the trans- horizontal deflection plates In an electrostatic
mitting station. cathode-ray tube (typical of laboratory oscillo-
horizontal axis The axis that is parallel to an as- scopes and some early television picture tubes), a
sumed horizontal surface (of the earth, for exam- pair of plates that produces an electric field to
ple) or the one so represented in a diagram. Also horizontally deflect the electron beam. Compare
horizontal beamwidth In a directional antenna horizontal directivity The radiation or reception
system, the angle, measured in the horizontal pattern of a directional antenna in the horizontal
plane, between the half-power points in the major plane.
lobe. horizontal-drive control See DRIVE CONTROL.
horizontal blanking See HORIZONTAL RETRACE horizontal dynamic convergence During the
BLANKING. scanning of a horizontal line in a color picture
horizontal-blanking pulse In a television signal, tube, convergence of the electron beams at the
the rectangular pedestal-shaped pulse that oc- aperture mask. Compare VERTICAL DYNAMIC
curs between the active horizontal lines to CONVERGENCE.
achieve horizontal retrace blanking. Compare horizontal field strength The field strength of sig-
VERTICAL-BLANKING PULSE. nals passing through an antenna in a horizontal
horizontal centering control See CENTERING plane. Compare VERTICAL FIELD STRENGTH.
CONTROL. horizontal-field-strength diagram A plot of hori-
horizontal channel The system of amplifiers, con- zontal field strength, usually in polar form. Com-
trols, and terminations that constitute the path of pare VERTICAL-FIELD-STRENGTH DIAGRAM.
the horizontal signal in an equipment, such as an horizontal flowcharting Flowcharting the move-
oscilloscope or graphic recorder. Compare VER- ment of documents or files, rather than the data
TICAL CHANNEL. bits themselves, through a digital system.
344 horizontal frequency • horizontal synchronization

horizontal frequency In television circuits, the coming signals whose electric lines of flux are
horizontal scanning frequency [i.e., the frequency horizontal. Compare VERTICAL POLARIZA-
at which the horizontal lines are traced (generally TION.
15.750 kHz)]. horizontal positioning control See CENTERING
horizontal frequency response The gain-vs- CONTROL.
frequency characteristic of the horizontal channel horizontal quantity The quantity measured along
of an oscilloscope or graphic recorder. Compare the X-axis of a graph represented by the horizon-
VERTICAL FREQUENCY RESPONSE. tal deflection of an oscilloscope beam. Compare
horizontal gain At a specified frequency, the over- VERTICAL QUANTITY.
all amplification of the horizontal channel of an horizontal recording See LATERAL RECORDING.
oscilloscope or graphic recorder. Compare VER- horizontal repetition rate See HORIZONTAL
horizontal-gain control A control, such as a po- horizontal resolution In a television picture, the
tentiometer, for adjusting horizontal gain. Com- number of picture elements (pixels) that can be
pare VERTICAL-GAIN CONTROL. discerned in a horizontal scanning line. Compare
horizontal-hold control In a television receiver, VERTICAL RESOLUTION.
the control for adjusting the horizontal oscilla- horizontal retrace In a cathode-ray device, such
tor frequency to prevent horizontal tearing of as an oscilloscope or television receiver, the rapid
the picture. Compare VERTICAL-HOLD CON- return of the electron beam to its starting point
TROL. after completing a horizontal sweep of the screen.
horizontal hum bars Dark, horizontal interferen- Compare VERTICAL RETRACE.
tial bars in a television picture, caused by HUM horizontal retrace blanking In oscilloscopes and
interference. television receivers, the automatic cutoff of the
horizontal linearity The precision of gain and de- electron beam during a horizontal retrace period,
flection in the horizontal channel of an oscillo- preventing an extraneous line on the screen dur-
scope, graphic recorder, or television receiver. A ing the period. Compare VERTICAL RETRACE
linear picture is a faithful (undistorted) reproduc- BLANKING.
tion of the original image. Compare VERTICAL horizontal scanning 1. The lateral sweeping of the
LINEARITY. electron beam in a cathode-ray tube. 2. The sam-
horizontal-linearity control In an oscilloscope or pling of x-axis values in a repetitive or nonrepeti-
television receiver, the control with which hori- tive sweep of that axis.
zontal linearity is adjusted. Compare VERTICAL- horizontal scanning frequency See HORIZONTAL
horizontal line frequency See HORIZONTAL FRE- horizontal sensitivity The signal voltage required
QUENCY. at the input of a horizontal channel for full hori-
horizontal lock See HORIZONTAL-HOLD CON- zontal deflection. Also see HORIZONTAL GAIN.
horizontally polarized wave An electromagnetic horizontal signal A signal serving as a horizontal
wave whose electric lines of flux are parallel to the quantity. Compare VERTICAL SIGNAL.
plane of the horizon. Compare VERTICALLY PO- horizontal sweep 1. In a cathode-ray tube, the
LARIZED WAVE. horizontal movement of the spot on the screen; in
horizontal multivibrator In a television receiver, a particular, the movement from left to right, dur-
15.750-kHz multivibrator that generates the hor- ing which a line of the image is formed on the
izontal sweep signal. screen. 2. The circuit that produces horizontal
horizontal oscillator In a TV receiver, the oscilla- sweep.
tor (usually a multivibrator) that generates the horizontal sweep frequency The frequency at
horizontal sweep signal. Compare VERTICAL OS- which horizontal sweep occurs; in a television re-
CILLATOR. ceiver, it is generally 15.750 kHz. Also called hor-
horizontal output stage In a television receiver, izontal sweep rate. Compare VERTICAL SWEEP
an output amplifier following the horizontal oscil- FREQUENCY.
lator. Compare VERTICAL OUTPUT STAGE. horizontal sweep rate See HORIZONTAL SWEEP
horizontal output transformer In a television re- FREQUENCY.
ceiver, the output transformer in the horizontal- horizontal-sync discriminator In a television re-
oscillator-output amplifier section. Also called ceiver, a circuit that compares horizontal sync-
FLYBACK TRANSFORMER. pulse phase with the phase of the signal from the
horizontal polarization Pertaining to an electro- horizontal sweep oscillator.
magnetic wave whose electric lines of flux are horizontal synchronization In a television re-
horizontal. In general, when the radiating ele- ceiver, synchronization of the horizontal compo-
ment of an antenna is horizontal, the electric nent of scanning with that of the transmitting
lines of flux in the transmitted waves are hori- camera. Also see HORIZONTAL SYNC PULSE.
zontal, and the antenna is most sensitive to in- Compare VERTICAL SYNCHRONIZATION.
horizontal sync pulse • hot line

horizontal sync pulse In a video signal, the pulse horn loading In a sound-transmission system, a
that synchronizes the horizontal scanning com- form of propagation that makes use of a horn-
ponent in a television receiver with that of the shaped speaker.
camera; it also triggers horizontal retrace and horn mouth The wider (radiating) end of a horn
blanking. Also see BACK PORCH. Compare VER- antenna or speaker. Compare HORN THROAT.


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