HALF-POWER POINT - A point on a waveform or radar beam that corresponds to half the
power of the maximum power point .
HALF-WAVE DIPOLE ANTENNA - An antenna, consisting of two rods (1/4 wavelength each) in
a single line, that radiates electromagnetic energy .
HALF-WAVE RECTIFIER - A rectifier using only one-half of each cycle to change ac to
pulsating dc [61 .
HALF-WAVE VOLTAGE DOUBLER - Two half-wave voltage rectifiers connected to double the
input voltage .
HAND OVER - The operation where one earth terminal yields control to another as a
satellite moves out of its area of coverage .
HARD COPY - The term given to humanly readable printed output from a computer.
HARD DISK - (See disk.)
HARD FERRITE - A ferrite with a very low wear rate when compared with the soft metal
laminations.
HARD METAL LAMINATIONS - (See core material, hard.)
HARD SOLID METAL - (see core material, hard.)
HARD-TUBE MODULATOR - A high-vacuum electron tube modulator that uses a driver for
pulse forming .
HARDWARE - The visible, physical equipment of a system, including the computer (cpu)
and related peripheral equipment; as distinguished from software.
HARMONIC - A frequency that is a whole-number multiple of a smaller base frequency .
HARMONIC DISTORTION - A signal non-linearity with harmonics of the fundamental in the
output when the input signal is sinusoidal.
HEAD CONTAMINATION - (See tape-to-head separation.)
HEAD CONTOUR - (1) The complex shape of the contacting surface of a head as a result of
manufacture, head lapping, or wear. (2) The contour of a head is always changing
throughout the head's life and, in many cases, is responsible for retiring the head.
HEAD CRASH - A term used for the damage to a hard disk caused by the physical contact
made between the magnetic read/write heads and the surface of the hard-disk platter.
HEAD POSITIONING - Placing a read/write head over a specified track on a disk or drum.
HEAD STICK - (1) A common word for a large increase in head-to-tape friction caused by
(a) a stick by-product exuded by conditions due to tape age, temperature/humidity, and
head-to-tape pressure, and (b) very smooth tapes coupled with large area heads. (2) See
also sticktion and stick-slip.
HEAD-TO-TAPE CONTACT - The degree that a tape's magnetic coating approaches the surface
of the record or reproduce head during normal operation.
HEATER - Same as a FILAMENT .
HEAT SHUNT - A device (preferably a clip-on type) used to absorb heat and protect
heat-sensitive components during soldering .
HEIGHT-FINDING RADAR - A radar that provides target altitude, range, and bearing data .
HELIX - (1) A spirally wound transmission line used in a traveling-wave tube to delay
the forward progress of the input traveling wave . (2) A large coil of wire. It acts as a
coil and is used with variable inductors for impedance matching of high-power transmitters
.
HELIX HOUSE - A building at a transmitter site that contains antenna loading, coupling,
and tuning circuits .
HENRY (H) - The electromagnetic unit of inductance or mutual inductance. The inductance
of a circuit is 1 henry when a current variation of 1 ampere per second induces 1 volt. In
electronics, smaller units are used, such as the millihenry (mH), which is one-thousandth
of a henry (H), and the microhenry (mH) which is one-millionth of a henry .
HERTZ (Hz) - A unit of frequency equal to one cycle per second .
HERTZ ANTENNA - A half-wave antenna that is installed some distance above ground and
positioned either vertically or horizontally .
HETERODYNE DETECTION - The use of an af voltage to distinguish between available
signals. The incoming cw signal is mixed with locally generated oscillations to give an af
output .
HETERODYNING - (1) The process of mixing two frequencies across a nonlinear impedance .
(2) The process of mixing the incoming signal with the local oscillator frequency. This
produces the two fundamentals and the sum and difference frequencies .
HEXADECIMAL - (1)Same as SEXADECIMAL. A number system with a base of sixteen; also
pertains to conditions, choices, or selections that have sixteen possible values or states
.(2)The number system with base 16 (0-9 and A-F). A represents 10; B represents 11; C
represents 12; D represents 13; E represents 14; and F represents 15. Used in some
computer systems.
HEXADECIMAL SYSTEM - Pertaining to the number system with a radix of sixteen. It uses
the ten digits of the decimal system and the first six letters of the English alphabet .
H-FIELD - Any space or region in which a magnetic force is exerted. The magnetic field
may be produced by a current-carrying coil or conductor, by a permanent magnet, or by the
earth itself .
HIGH FREQUENCY - The band of frequencies from 3 megahertz to 30 megahertz .
HIGH-FREQUENCY COMPENSATION - See PEAKING COIL .
HIGH-LEVEL LANGUAGES - Programming languages that allow the programmer to write
programs in English-like terms and symbols and mathematical notation, rather than the 0's
and 1's used by the computer. These high-level programs must be translated into machine
language before the computer can execute them. FORTRAN, Ada, COBOL, and BASIC are
examples.
HIGH-LEVEL MODULATION - Modulation produced in the plate circuit of the last radio
stage of the system .
HIGH-PASS FILTER - A filter that passes a majority of the high frequencies on to the
next circuit and rejects, or attenuates, the lower frequencies. Also called a
LOW-FREQUENCY DISCRIMINATOR .
HITS PER SCAN - The number of times an rf beam strikes a target per antenna revolution
.
HOLE FLOW - In the valence band, a process of conduction in which electrons move into
holes, thereby creating other holes that appear to move toward a negative potential. (The
movement of holes is opposite the movement of electrons.)
HORIZONTAL AXIS - On a graph, the straight line axis that is plotted from left to right
.
HORIZONTAL-DEFLECTION PLATES - A pair of parallel electrodes that moves the electron
beam from side to side in a CRT .
HORIZONTALLY POLARIZED - Waves radiated with their E field component parallel to the
earth's surface .
HORIZONTAL PATTERN - The part of a radiation pattern that is radiated in all directions
along the horizontal plane .
HORIZONTAL PLANE - An imaginary plane that is tangent (or parallel) to the earth's
surface at a given location .
HORN - A funnel-shaped section of waveguide used as a termination device and as a
radiating antenna .
HORN ANTENNA - See HORN RADIATOR .
HORN RADIATOR - A tapered, tubular or rectangular microwave antenna that is widest at
the open end .
HORSEPOWER - The English unit of power equal to work done at the rate of 550
foot-pounds per second; equal to 746 watts of electrical power .
HORSESHOE MAGNET - A permanent magnet or electromagnet bent into the shape of a
horseshoe or having a U-shape to bring the two poles near each other .
HOST COMPUTER - The main or controlling computer in a distributed data processing
network (ddp).
HOT CARRIER - A carrier, which may be either a hole or an electron, that has relatively
high energy with respect to the carriers normally found in majority-carrier devices .
HOT-CARRIER DIODE - A semiconductor diode in which hot carriers are emitted from a
semiconductor layer into the metal base. Also called HOT-ELECTRON DIODE. An example is the
Schottky barrier diode .
HOT-WIRE METER MOVEMENT - A meter movement that uses the expansion of a heated wire to
move the pointer of a meter; measures dc or ac .
H-TYPE T-JUNCTION - A waveguide junction in which the junction arm is parallel to the
magnetic lines of force in the main waveguide .
HYBRID CIRCUIT - A circuit where passive components (resistors, capacitors) are
deposited onto a substrate made of glass, ceramic, or other insulating material. Then the
active components (diodes, transistors) are attached to the substrate and connected to the
passive components on the substrate with a very fine wire .
HYBRID COMPUTER - A computer that combines the functions of both analog and digital
computers.
HYBRID ICs - Two or more integrated circuit types, or one or more integrated circuit
types and discrete components on a single substrate .
HYBRID JUNCTION - A waveguide junction that combines two or more basic T-junctions .
HYBRID MIXER - See BALANCED MIXER .
HYBRID RING - A hybrid-waveguide junction that combines a series of E-type T-junctions
in a ring configuration. When properly terminated, energy is transferred from any one
branch into any two of the remaining three branches .
HYDROMETER - An instrument used to measure specific gravity. In batteries hydrometers
are used to indicate the state of charge by the specific gravity of the electrolyte .
HYSTERESIS - The time lag of the magnetic flux in a magnetic material behind the
magnetizing force producing it. Caused by the molecular friction of the molecules trying
to align themselves with the magnetic force applied to the material .
HYSTERESIS LOSS - The power loss in an iron-core transformer or other
alternating-current device as a result of magnetic hysteresis .
