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HELIX—(1) A spirally wound transmission line used in a traveling-wave tube to delay the forward progress
of the input traveling wave [11]. (2) A large coil of wire. It acts as a coil and is used with variable
inductors for impedance matching of high-power transmitters [17].
HELIX HOUSE—A building at a transmitter site that contains antenna loading, coupling, and tuning
circuits [17].
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 (
m
H)
which is one-millionth of a henry [2].
HERTZ (Hz)—A unit of frequency equal to one cycle per second [2].
HERTZ ANTENNA—A half-wave antenna that is installed some distance above ground and positioned
either vertically or horizontally [10].
HETERODYNE DETECTION—The use of an a.f. voltage to distinguish between available signals. The
incoming cw signal is mixed with locally generated oscillations to give an a.f. output [12].
HETERODYNING—(1) The process of mixing two frequencies across a nonlinear impedance [12]. (2)
The process of mixing the incoming signal with the local oscillator frequency. This produces the two
fundamentals and the sum and difference frequencies [17].
HEXADECIMAL—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 [13].
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 [13].
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 [11].
HIGH FREQUENCY—The band of frequencies from 3 megahertz to 30 megahertz [17].
HIGH-FREQUENCY COMPENSATION—See PEAKING COIL [8].
HIGH-LEVEL MODULATION—Modulation produced in the plate circuit of the last radio stage of the
system [12].
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
[9].
HITS PER SCAN—The number of times an RF beam strikes a target per antenna revolution [18].
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.) [7]
HORIZONTAL AXIS—On a graph, the straight line axis that is plotted from left to right [10].
HORIZONTAL-DEFLECTION PLATES—A pair of parallel electrodes that moves the electron beam
from side to side in a CRT [6].
