Glossary Terms Beginning H

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H.221: Framing protocol used as part of H.320 (ITU-T standard).
H.230: Control and indication protocol used as part of H.320 (ITU-T standard).
H.242: Communications procedure protocol used as part of H.320 (ITU-T standard).
H.261: Audio compression algorithm standard (ITU-T standard).
H.263+: Further refinement of H.320 to improve performance (ITU-T standard).
H.320: Specification for video-conferencing over ISDN (ITU-T standard).
HDTV: High definition television: television system with approximately twice the horizontal and twice the vertical resolution of current 525-line and 625-line systems, with component colour coding, picture aspect ratio of 16:9 and a frame rate of at least 24 Hz.
Hertz: Hz: term for the basic measure of an electromagnetic wave completing a full oscillation from its positive to its negative pole and back again in what is known as a cycle; thus 1 Hertz is equal to one cycle per second.
Hop: A single Earth-satellite-Earth path.
Horn: See Feedhorn.
HPA: High-power amplifier.
HSD: High-speed data.
Hz: Unit of frequency, where 1 Hz describes one cycle per second; 1 kHz = 1000 Hz (1 × 103 Hz); 1 MHz = 1000 000 Hz (1 × 106 Hz); 1 GHz = 1000 000 000 Hz (1 × 109Hz).