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H

HEATER

Same as a FILAMENT [6].

HEIGHT-FINDING RADAR

A radar that provides target altitude, range, and bearing data [18].

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

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 (μH) which is one-millionth of a henry [2].


HERTZ

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].



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