Also referred to as B-Picture. Bi-directional predictive-coded picture. A picture that is coded using motion compensated prediction from past pictures (I-pictures) and/or future reference pictures (P-pictures). In this process background and/or other information is stored for re-use in future frames so that the transfer speed of a digital video stream is increased because it does not have to repeatedly send redundant information.
A form of transmission encryption developed by Scientific-Atlanta. In such transmissions MAC (Multiplexed Analog Component) signals are time-multiplexed with a digital burst containing digitized audio components, video synchronizing, customer authorization and other 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 levels of a traveling wave tube (TWT) in order to obtain more linear operation.
Band Pass Filter
An active or passive circuit which allows signals with the desired frequency range to pass through but impedes signals outside of this frequency range from getting through. This type of filter is used mainly when adjacent frequencies are causing interference with the desired frequencies.
A measure of spectrum (frequency) use or capacity. For instance, a voice tranmission by telephone requires a bandwidth of about 3000 cycles per second (3 KHz). 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 from a television camera, satellite television receiver, or video tape recorder in an intermediate frequency (IF) range. Baseband signals can be viewed only on studio monitors. To display the baseband signals on a standard television the signal must be modulated to a VHF or UHF frequency which the television set has a capability of receiving.
Baud (Bits at unit density)
The rate of data tranmission based on the number of signal elements or symbols transmitted per second. Today most digital signals are characterized in bits per second.
A low power carrier transmitted by a satellite which supplies the controlling engineers on the ground with a means of monitoring telemetry data, tracking information or conducting propagation experiments. This beacon is usually a horn or omni transmission antenna.
The angle or conical shape of the tranmission beam the antenna projects. Large antennas have narrower beamwidths and can pinpoint satellites in space or dense traffic areas in terrestrial situations more precisely. Tighter beamwidths thus deliver higher levels of power with increased performance characteristics and less chance of causing interference on adjacent satellites or terrestrial services.
Slang term for almost any satellite in orbit around the earth.
A single digital unit of information composed of a 0 or a 1. The bit rate is used to measure transmission capacity.
Bit Error Rate (BER)
The fraction of a sequence of digital 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. A general rule of thumb is that the lower the number on the left and the higher the number on right the better the signal. 0.0-6 is a near perfect signal, while a reading of 3.0-2 is a very weak signal.
The speed of a digital transmission measured in bits per second.
Also referred to as a circular blackout. A blackout circle is a program parameter that defines a geographical area based on x,y,z coordinates that will be denied authorization for a particular signal or service. This means that each IRT/IRD within the blackout region will be deauthorized for signals containing the blackout information. Each IRT/IRD is defined by an x,y,z coordinate which expresses it's geographical location.
An ordinary television signal consists of 30 separate still pictures or frames sent every second. These frames occur so rapidly that 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 blanking interval special data packets may be sent which will not be picked up by standard television receivers. VITS (Vertical Interval Timing Signals) are one type of signal that is sent to your television during this blanking segment. This tells your television when to display the next frame sequence.
Block Down Converter
A device used to convert the standard C-Band downlink signals of 3.7 to 4.2 GHz signal down to the L-Band, UHF or lower frequencies (1.5 GHz and lower).
Corporate communications tool utilizing video transmission of information via satellite. Common uses of business television include teleconferencing, training seminars and product information profiles.
One byte of digital video information contains a packet of bits, which is usually, but not always, composed of eight bits. In the digital video domain a byte is used to represent the luminance or chrominance level. 1000 bytes = one kilobyte (1 kb). 1,000,000 bytes = one megabyte (1 MB)
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