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C...

C-Band

This is the designation for the frequency band between 4 and 8 GHz.  Satellite uplink transmissions typically use a range from 5.925 GHz to 6.425 GHz.  Satellite downlink transmissions typically use a range from 3.7 GHz to 4.2 GHz.

Carrier to Noise Ratio (C/N)

The ratio of the received carrier power and the noise power in a given bandwidth, expressed in decibels (dB).  This figure is directly related to the G/T (antenna gain/noise temperature) and S/N (signal/noise).  In a video signal the higher the carrier/noise ratio, the higher the level of picture quality.

Carrier

The center frequency of the basic radio, television, or telephony transmit signal.   The carrier in an analog signal is modulated by manipulating it's amplitude (strength in dB) or frequency (width in MHz) in relation to the incoming signal.   Satellite carriers operating in the analog mode are usually frequency modulated.

Carrier Frequency

An assigned frequency value for audio, data or video signal transmission.   Microwave and satellite communication transmitters operate in the band spanning 1GHz to 14GHz. (A GHz is one billion cycles per second.)

Cassegrain Antenna

A specific type of antenna assembly that uses a subreflector at the dish focal point to redirect a signal to the main reflector or surface of the dish.

Category Epoch

A variable unit of time during which an authorization message received by decoders is valid.  An example of it's use is when a subscriber is receiving a free promotional authorization for a set period of time.  The category epoch will have the duration of the promotional period as it's time limit for the subscriber's decoder.

Category Epoch Number

A number that the UCS (Uplink Control System) assigns to each category epoch is defined in it's encryption protocols.

CDMA

Code Division Multiple Access.  This refers to a multiple-access scheme whereby stations use spread-spectrum modulations and orthogonal codes to avoid interference with one another's signals.

Channel

A frequency band designation in which specific bandwidth parameters are established.   Satellites channels are referred to as transponders.  Channel frequencies in the United States are specified by the Federal Communications Commision.  Television signals require a minimum of 6 MHz to carry all necessary picture details and information.

Chrominance

The color information contained in a video signal.  This information is usually defined in terms of hue and saturation.  The video signal is made up of chrominance (color) and luminance (brightness) information.  The symbols are Cr (chrominance) and Cb (luminance).

Circular Polarization

Used mainly on international satellites, circular polarization uses right-hand and left-hand rotation to distinguish between signals of opposite polarity.  U.S. domestic satellites generally use vertical and horizontal polarization to distinguish separate signals.  On some satellites both right-hand and left-hand signals may be transmitted simultaneously at the same frequency.  This capability may effectively double the channel carrying capacity of a given satellite. Instead of positioning the microwave energy in a plane, whether vertical or horizontal, circular polarization is transmitted in a circular pattern, that rotates in either a clockwise or a counter-clockwise direction. Although your regular feedhorn can still pick up circularly polarized signals, you end up losing half of the available signal. This can make the difference between a noise-free picture and one that is not tolerably viewable.

Clamp

A video processing circuit that removes the energy dispersal signal component from the video waveform.

Clarke Orbit

Named for noted science fiction writer Arthur C. Clarke, who postulated in the 1945 issue of "Wireless Magazine" that satellites placed in orbit 22, 237 miles above the earth with a matching rotational speed would remain in what we refer to as a geosynchronous orbit.  Satellites placed in this orbital plane above the equator would appear to be motionless from a given point on the earth even though they are traveling through space at thousands of miles per hour.

C/No

The carrier to noise ratio when measured at Radio Frequency (RF) or at Intermediate Frequency (IF).

Codec

Encoder/Decoder system for digital transmissions.

Coding

The third step in the analog-to-digital conversion process in which the information is written in binary form.

Co-Location

The ability of multiple satellites to share the same approximate geostationary orbital position due to the use of different frequency bands.

Color Subcarrier

A subcarrier that is added to the main video carrier to convey color information.   In NTSC systems the color subcarrier is centered on a frequency located at 3.79545 MHz when referenced to the main video carrier center frequency.

Common Carrier

Any organization which operates communication circuits used by other people.   Common carriers include the telephone companies as well as the owners of the communication satellites.  RCA, Comsat, Direct Net Telecommunications, AT&T among others are listed as common carriers.  Common carriers are required to file fixed tariffs for specific services.

Companding

A noise-reduction technique that applies single compression at the transmitter and complementary expansion at the receiver.

Component Video

A video signal in which luminance and chrominance information is kept separate rather than being combined as in composite video signals.  Component processing and routing requires three wires to route the signal  and component recording requires three separate tracks on a magnetic tape.  These three component values are usually designated as Y, R-Y, B-Y or Y, U, V.

Composite Baseband

The unclamped and unfiltered output of the satellite receiver's demodulator circuit.   This contains the video information as well as all transmitted subcarriers.

Composite Video

Composite video combines the chrominance and luminance information of a video signal by encoding the output of the red, green and blue channels into the Y, I and Q signals.   A composite video signal includes blanking and sync informaion.  Composite video is the standard for broadcast transmissions of video signals.

Compression

Reduction of dynamic range.  Used in broadcasting to achieve greater or more uniform loudness.  This is one of the reasons your commercials have louder audio levels than your programs.  The audio segment of the commercials signal has been compressed.

Conus

Contiguous United States.  All the states except for Hawaii and Alaska.

Cross Modulation

A form of signal distortion in which modulation from one or more RF carriers is imposed on another carrier.  Generally referred to as an interference case.

C/T

Carrier to noise temperature ratio.  Generally rated in degrees Kelvin.  This is a measurement of noise picked up by electronic equipment at given values of temperature.

 

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