C-Band
This is the band between 4 and 8 GHz with the 6 and 4 GHz band being used for satellite communications. Specifically, the 3.7 to 4.2 GHz satellite communication band is used as the down link frequencies in tandem with the 5.925 to 6,425 GHz band that serves as the uplink.

C/No
Carrier-to-noise ratio measured either at the Radio Frequency (RF) or Intermediate Frequency (IF).

C/T
Carrier-to-noise-temperature ratio.

Carrier
The basic radio, television, or telephony center of frequency transmit signal. The carrier in an analog signal. is modulated by manipulating its amplitude (making it louder or softer) or its frequency (shifting it up or down) in relation to the incoming signal. Satellite carriers operating in the analog mode are usually frequency modulated.

Carrier Frequency
The main frequency on which a voice, data, or video signal is sent. Microwave and satellite communications transmitters operate in the band from 1 to 14 GHz (a GHz is one billion cycles per second).

Carrier to Noise Ratio (C/N)
The ratio of the received carrier power and the noise power in a given bandwidth, expressed in dB. This figure is directly related to G/T and S/N; and in a video signal the higher the C/N, the better the received picture.

Cassegrain Antenna
The antenna principle that utilizes a subreflector at the focal point which reflects energy to or from a feed located at the apex of the main reflector.

CDMA
Code division multiple access. Refers to a multiple-access scheme where stations use spread-spectrum modulations and orthogonal codes to avoid interfering with one another.

Channel
A frequency band in which a specific broadcast signal is transmitted. Channel frequencies are specified in the United States by the Federal Communications Commission. Television signals require a 6 MHz frequency band to carry all the necessary picture detail.

Circular Polarization
Unlike many domestic satellites which utilize vertical or horizontal polarization, the international Intelsat satellites transmit their signals in a rotating corkscrew-like pattern as they are down-linked to earth. On some satellites, both right-hand rotating and left-hand rotating signals can be transmitted simultaneously on the same frequency; thereby doubling the capacity of the satellite to carry communications channels.

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

Clarke Orbit
That circular orbit in space 22,237 miles from the surface of the earth at which geosynchronous satellites are placed. This orbit was first postulated by the science fiction writer Arthur C. Clarke in Wireless World magazine in 1945. Satellites placed in these orbits, although traveling around the earth at thousands of miles an hour, appear to be stationary when viewed from a point on the earth, since the earth is rotating upon its axis at the same angular rate that the satellite is traveling around the earth.

Co-Location
Ability of multiple satellites to share the same approximate geostationary orbital assignment frequently due to the fact that different frequency bands are used.

Codec
Coder/decoder system for digital transmission.

Color Subcarrler
A subcarrier that is added to the main video signal to convey the color information. In NTSC systems, the color subcarrier is centered on a frequency of 3.579545 MHz, referenced to the main video carrier.

Common Carrier
Any organization which operates communications circuits used by other people. Common carriers include the telephone companies as well as the owners of the communications satellites, RCA, Comsat, Direct Net Telecommunications, AT&T and others. 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.

Composite Baseband
The unclamped and unfiltered output of the satellite receiver's demodulator circuit, containg the video information as well as all transmitted subcarriers.

Conus
Contiguous United States. In short, all the states in the U.S. except Hawaii and Alaska.

Cross Modulation
A form of signal distortion in which modulation from one or more RF carrier(s) is imposed on another carrier.

CSU
Channel service unit. A digital interface device that connects end-user equipment to the local digital telephone loop. CSU is frequently coupled with DSU (see below) as CSU/DSU.

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