ComStream CM601, Installation And Operation Manual

Page: 145 / 228

Glossary 7
Rx or RX receive
SCC satellite control channel – main application is monitoring and controlling remote
units from a central hub facility
SCPC
single channel per carrier
SD
send data – also referred to as transmit data
SIU
software interface unit
SMS
Satellite Multiservice System – a Eutelsat service for general satellite data
communications
spectral inversion Condition typically caused by RF equipment that uses the image of the earth
station’s output spectrum instead of the true spectrum. (Note: There is nothing
wrong with systems that do this; simply compensate for the condition.) Example:
A 70 MHz modem IF output contains a mirror-like image at -70 MHz. If the RF
equipment is designed to use the -70 MHz image and the receive RF does not
similarly invert the signal (that is, undo the inversion), then there is a spectral
inversion and the signal cannot be recognized by the receiver.
sps symbols per second
SQ signal quality
ST station timing clock
sync synchronization
TCXO temperature-compensated crystal oscillator
TDM time division multiplexing – technique for combining several channels into one
transmission path in which each channel is allotted a specific position in the signal
stream based upon time
TDMA time division multiple access – satellite transmission technique in which many
distant earth stations systematically share the same carrier frequency on a time-
division basis—all earth stations operate on the same carrier frequency but only in
short bursts and only one at a time
TR
terminal ready
TT
transmit timing clock – provided by DTE
Tx or TX
transmit