A method of transmitting and scrambling television signals. In such transmissions MAC (Multiplexed Analog Component) signals are time-multiplexed with a digital burst containing digitized sound, video synchronizing, authorization, and information.
A terrestrial communications channel linking an earth station to a local switching network or population center.
The process of reducing the input and output power levels of a traveling wave tube to obtain more linear operation.
Band Pass Filter
An active or passive circuit which allows signals within the desired frequency band to pass through but impedes signals outside this pass band from getting through.
A measure of spectrum (frequency) use or capacity. For instance, a voice transmission by telephone requires a bandwidth of about 3000 cycles per second (3KHz). A TV channel occupies a bandwidth of 6 million cycles per second (6 MHz) in terrestrial Systems. In satellite based systems a larger bandwidth of 17.5 to 72 MHz is used to spread or "dither" the television signal in order to prevent interference.
The basic direct output signal in an intermediate frequency based obtained directly from a television camera, satellite television receiver, or video tape recorder. Baseband signals can be viewed only on studio monitors. To display the baseband signal on a conventional television set a "modulator" is required to convert the baseband signal to one of the VHF or UHF television channels which the television set can be tuned to receive.
The rate of data transmission based on the number of signal elements or symbols transmitted per second. Today most digital signals are characterized in bits per second.
Low-power carrier transmitted by a satellite which supplies the controlling engineers on the ground with a means of monitoring telemetry data, tracking the satellite, or conducting propagation experiments. This tracking beacon is usually a horn or omni antenna.
The angle or conical shape of the beam the antenna projects. Large antennas have narrower beamwidths and can pinpoint satellites in space or dense traffic areas on the earth more precisely. Tighter beamwidths thus deliver higher levels of power and thus greater communications performance.
Slang for a communications satellite located in geosynchronous orbit.
A single digital unit of information
Bit Error Rate
The fraction of a sequence of message bits that are in error. A bit error rate of 10-6 means that there is an average of one error per million bits.
The speed of a digital transmission, measured in bits per second.
An ordinary television signal consists of 30 separate still pictures or frames sent every second. They occur so rapidly, the human eye blurs them together to form an illusion of moving pictures. This is the basis for television and motion picture systems. The blanking interval is that portion of the television signal which occurs after one picture frame is sent and before the next one is transmitted. During this period of time special data signals can be sent which will not be picked up on an ordinary television receiver.
Block Down Converter
A device used to convert the 3.7 to 4.2 KHz signal down to UHF or lower frequencies (1 GHz and lower).
BPSK (Binary Phase Shift Keying)
A digital modulation technique in which the carrier phase can have one of two possible values, namely 0 degrees or 180 degrees.
A single large circular beam that covers a large geographic area
The sending of one transmission to multiple users in a defined group (compare to unicast).
BSS (Broadcast Satellite Service)
This is the ITU designation but DBS or Direct Broadcast Service is more commonly used term in the satellite industry.
Corporate communications tool involving video transmission of information via satellite.
Common uses of business television are for meetings, product introductions and training.
A shaped piece of waveguide directing signal from the feed to the LNA behind the antenna.
Use of satellite, local area network, wide area network or metropolitan area network as an alternative transmission facility.