Satellite Glossary
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Scrambler to Wavelength
Scrambler - A device used to electronically alter a signal so that it can only be viewed on a receiver equipped with a special decoder.
Signal to Noise Ratio (S/N) - The ratio of the signal power and noise power. A video S/N of 54 to 56 dB is considered to be an excellent S/N, that is, of broadcast quality. A video S/N of 48 to 52 dB is considered to be a good S/N at the headend for Cable TV.
Single-Channel-Per-Carrier (SCPC - A method used to transmit a large number of signals over a single satellite transponder.
Snow - A form of noise picked up by a television receiver caused by a weak signal. Snow is characterized by alternate dark and light dots appearing randomly on the picture tube. To eliminate snow, a more sensitive receive antenna must be used, or better amplification must be provided in the receiver (or both). Satellite TV service doesn't have any snow.
Solar Outage - An outage that occurs when the sun passes near or behind the satellite and within the field of view of the antenna. This field of view is usually wider than the beamwidth.
Spectrum - The range of electromagnetic radio frequencies used in transmission of voice, data and television.
Spillover - Satellite signal that falls on locations outside the beam pattern's defined edge of coverage.
Telemetry, Tracking and Control - The facility which monitors and controls the proper functioning of a satellite in space. Abbreviated TT&C.
Transceiver - A combination transmitter and receiver.
Transmitter - An electronic device containing an oscillator and modulator that produces electromagnetic wave signal for transmission by an antenna.
Transponder - A part contained in a satellite that is a combination receiver, frequency converter, and transmitter package. Communications satellites typically have between 12 and 24 onboard transponders.
TVRO - Abbreviation for Television Receive Only. The satellite receiving antenna used in small home systems.
Ultra High Frequency (UHF) - The band in the 500 to 900 MHz range, including TV channels 14 through 83.
Unicast - Transmission of a copy of every packet to every receiver.
Uplink - Transmission from earth to a satellite. See also Downlink.
Very High Frequency - Abbreviated VHF. The band in the 30 to 300 MHz range, including TV channels 2 through 13.
VSAT - Abbreviation for Very Small Aperture Terminal. Refers to small earth stations, usually in the 1.2 to 2.4 meter range.
Wavelength - The distance while traveling at the speed of light that a radio wave will travel during a single cycle.
