The process associated with analog-digital conversion in which the continuous analog waveform is divided into discrete moments in time.


Any object in orbit around another object.

Satellites circle our globe in several types of orbits.

Geosynchronous satellites are those that are sophisticated electronic communications relay stations orbiting 22,237 miles above the equator moving in a fixed orbit at the same speed and direction of the earth (about 7,000 mph east to west). These satellites are referred to as geostationary as they always appear to be motionless from a point on earth.

Polar orbit satellites orbit along the polar axis of the earth and never appear to be stationary.

SCPC - Single Channel Per Carrier

A method used to transmit a large number of signals over a single satellite transponder.

Scalar Feed

A type of horn antenna feed which uses a series of concentric rings to capture signals that have been reflected toward the focal point of a parabolic antenna.


An encryption designation indicating that the channel is encrypted. Only decoders belonging to the same network can receive the programming.


A device used to electronically alter a signal so that it can only be viewed or heard on a receiver equipped with a special decoder.


Sequentiel Coleur A Memoire. European video standard with image format 4:3, 625 lines, 50 Hz and 6MHz video bandwidth with a total 8 MHz of video channel width. The major difference between PAL and SECAM is that the chrominance is FM modulated in SECAM.


A grouping of 20 virtual channels specified in a single message in a Virtual Channel Map.

Service Component

An element of a service that is of a single type, such as a video data stream, or an audio data stream, or an ECM stream, or subtitles, or control data, or any other data stream that is a meaningful portion of a service. In general, each service component is carried in packets labeled with a single reference number (PID).

Service Control Channel

The message stream that conveys the servicing map message and other service related information messages relating solely to a single service.


Off-axis response of an antenna.

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.


An adjustment that compensates for slight variance in angle between identical senses of polarity generated by two or more satellites.

Slant Range

The length of the path between a communications satellite and an associated earth station.


That longitudinal position in the geosynchronous orbit into which a communications satellite is "parked". Above the United States, communications satellites are typically positioned in slots which are based at two degree intervals.


Satellite master antenna television. A satellite broadcast service available to hotels, motels, apartment complexes, etc.


Society of Motion Picture and Television standards, advancing the theory and application of film, television, video, computer imaging, telecommunications, and the related arts and sciences. The SMPTE time code standard (hr:min:sec:frame) is used to identify video frames.


An optional interface used to synchronize the UCS time with the studio time.


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).

Solar Outage

Solar outages occur when an antenna is looking at a satellite, and the sun passes behind or near 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. They occur twice yearly in the spring and in the fall.


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


Satellite signal that falls on locations outside the beam pattern's defined edge of coverage.

Spin Stabilization

A form of satellite stabilization and attitude control which is achieved through spinning the exterior of the spacecraft about its axis at a fixed rate.


A passive device (one with no active electronic components) which distributes a television signal carried on a cable in two or more paths and sends it to a number of receivers simultaneously.

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 such as Hawaii, Alaska and Puerto Rico.

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 unauthorized earth stations. Both military and civil satellite applications have developed for spread spectrum transmissions.


Solid state power amplifier. A VSLI solid state device that is gradually replacing Traveling Wave Tubes in satellite communications systemsbecause they are lighter weight and are more reliable.


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


A continuous receipt of packets that have an identical packet ID.


A second signal "piggybacked" onto a main signal to carry additional information. In satellite television transmission, the video picture is transmitted over the main carrier. The corresponding audio is sent via an FM subcarrier. Some satellite transponders carry as many as four special audio or data subcarriers whose signals may or may not be related to the main programming.

Synchronization (Sync)

The process of orienting the transmitter and receiver circuits in the proper manner in order that they can be synchronized . Home television sets are synchronized by an incoming sync signal with the television cameras in the studios 60 times per second. The horizontal and vertical hold controls on the television set are used to set the receiver circuits to the approximate sync frequencies of incoming television picture and the sync pulses in the signal then fine tune the circuits to the exact frequency and phase.


The instantaneous alignment of two or more events in time. Events may occur at irregular intervals, though at the same instant and still be synchronous.


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