Glossary of Terms and acronyms

Satellite:
Short hand for artificial satellite (the moon is a natural satellite). Usually refers to an electronic radio communications repeater orbiting above the earth. However, other applications are involved such as earth observation systems, signals intelligence gathering spacecraft and so on.

Set Top Box:
Term originally used to describe a channel selector allowing households to watch broadband cable channels. Subsequently also used to describe the in-door element of a satellite receiver. Usually the STB contains some form of decoder to allow access to encrypted and scrambled pay-TV channels. The digital STB also has the function of converting the digital TV channels to the analogue form needed to view on a standard TV set.

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.

Solar Outage:
Solar outages occur when an antenna is looking at a satellite, and the sun passes behind or nearly behind the satellite and within the field of view of the antenna. This field of view is usually wider than the beamwidth. Solar outages can be exactly predicted as to the timing for each site.

Spectrum:
The range of electromagnetic radio frequencies used in transmission of voice, data and television.

Spectrum Auction:
Method by which some governments sell certain frequency bands to potential users using an auctioning process. Normally governments hand out spectrum to users on an administrative basis (i.e. they get it free of charge) but this is increasingly seen as an economically inefficient method of allocating a scarce resource where there is more demand than supply. Auctioning has been used by the FCC for spectrum for DBS and PCN services.

Spot Beam:
A focused antenna pattern sent to a limited geographical area. Spot beams are used by domestic satellites to deliver certain transponder signals to geographically well defined areas. Spot beams offer the potential of spectrum re-use; the same bands of frequency can be used with different spotbeams. This is particularly useful in the multimedia satellite environment.

Spread Spectrum:
The transmission of a signal using a much wider bandwidth and power than would normally be required. Spread spectrum also involves the use of narrower signals that are frequency hopped through various parts of the transponder. Both techniques produce low levels of interference between the users. They also provide security in that the signals appear as though they were random noise to unauthorised earth stations. Both military and civil satellite applications have developed for spread spectrum transmissions.

STS-1:
Sonet based transmission rate of 5184 MBit/s.

SSPA:
Solid state power amplifier. A VSLI solid-state device that is used in some satellites where only low power output is required.

Subscriber Management Services (SMS):
General term to describe the management of the subscription side of pay-TV services including authorisation of smart cards, billing of customers, customer enquiries and support.

Stationkeeping:
Minor orbital adjustments that are conducted to maintain the satellite's orbital assignment within the allocated "box" within the geostationary arc.

Switch-Board in the Sky:
Also known as an "Intelligent Bird" this is a short hand term to describe a communications satellite that also carries a switching payload rather like a telephone exchange in the sky. Such switching systems go beyond switching the complete uplink signal to a transponder to another transponder; the various messages within each uplink can be switched. Concept is used in advanced mobile communications satellites and is intended for use in Ka-band ATM or multimedia satellites.