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H

Harmonic : Integer multiples of the fundamental frequency being generated, harmonics are present if a signal is not perfectly sinusoidal or is undergoing intermodulation distortion. Harmonics located outside the desired band for transmission are normally removed with low-pass filters to avoid interference to other radio services.

Harmonic (of a ham)  : Slang term for the child of a ham.

Hellschreiber (Hell) : A digital mode for sending and receiving text using facsimile (fax) technology.

Henry :(H) The unit for inductance

Hertz : Hz - The unit of measure for frequency.

HF : High Frequency. Frequencies in the range 3MHz to 30MHz.

High Pass Filter : A filter designed to pass high frequency signals.

Horizontal Polarization : An antenna or radio signal in which the electric field is propagated parallel to the surface of the Earth.

HT : Handheld Transceiver or HandiTalkie. Usually refers to transceivers that operate in the 2m and 70cm amateur bands; these are self-contained hand-held radios which include an antenna and battery and transmit at low power.