32 Glossary: G-S
Description
This article is from the TeleVision Receive Only Satellite-TV FAQ, by TVRO Hobbyists drlev@hotmail.com with numerous contributions by others.
32 Glossary: G-S
Geostationary (Geosynchronous): Refers to a satellite's orbit which is
synchronized to the rotation of the earth, thereby causing the
satellite to appear to remain stationary. Communications satellites
are parked in geosynchronous orbit 22,300 miles above the equator.
HDTV (High Definition Television): A developing technology for
producing and distributing television of greater clarity and scope by
increasing the number of lines used to comprise the television
picture.
Headend: Generally, a cable television system's master control
operation where signals are received (sometimes from a variety of
sources: satellite, land-lines, microwave, even taped or live
origination) and delivered on various cable system channels.
IRD (Integrated Receiver and Decoder): A small box housing the
electronics enabling the user to downlink and decode satellite
signals.
Ku-Band: Frequency range from approximately 11 to 14 GHz (billion
cycles per second) used by communications satellites.
LNB (Low noise block downconverter): A special amplifier that boosts
the satellite signal while contributing a negligible amount of
noise. It also converts a signal to a more suitable block of
frequencies for use by an earth station receiver.
Polarization: A satellite transmission signal has either a vertical,
horizontal, or circular orientation; a satellite can be all vertical
or all horizontal; if a satellite is cross-polarized, it can transmit
both ways and therefore has twice the usable delivery capacity.
Rain Fade: (communications usage) Signal weakening due to the presence
of severe precipitation somewhere along the signal path.
SCPC (Single-Channel-Per-Carrier): A type of FDM transmission where
each carrier contains only one communications channel. Many VSAT
networks utilize SCPC transmission.
Scrambling: (TV usage) Altering a TV signal transmission so it cannot
be received without an operating decoder.
Split-Transponder: A method of transmitting two conventional digital
or analog television signals through a satellite transponder
simultaneously. Each of the two signals is transmitted at half the
power normally available to a full transponder.
Subcarrier: A smaller bandwidth channel modulated on to the main
channel to add information (like audio), perform a function (burst) or
act as a reference.
Sun Transit: A time when the sun appears to transit or pass directly
behind the satellite thereby briefly "blinding" the earth station's
ability to see the satellite. This alignment occurs twice a year at
predictable times prior to the vernal equinox and after the autumnal
equinox.
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