T1
The transmission bit rate of 1.544 millions bits per second. This is also equivalent to the ISDN Primary Rate Interface for the U.S. The European T1 or E1 transmission rate is 2.048 million bits per second.

T3 Channel (DS-3)
In North America, a digital channel which communicates at 45.304 Mbps.

TDMA
Time division multiple access. Refers to a form of multiple access where a single carrier is the shared by many users. Signals from earth stations reaching the satellite consecutively are processed in time segments without overlapping.

TI - Terrestrial Interference
Interference to satellite reception caused by ground based microwave transmitting stations.

Transmitter
An electronic device consisting of oscillator, modulator and other circuits which produce a radio or television electromagnetic wave signal for radiation into the atmosphere by an antenna.

Transponder
A combination receiver, frequency converter, and transmitter package, physically part of a communications satellite. Transponders have a typical output of five to ten watts, operate over a frequency band with a 36 to 72 megahertz bandwidth in the L, C, Ku, and sometimes Ka Bands or in effect typically in the microwave spectrum, except for mobile satellite communications. Communications satellites typically have between 12 and 24 onboard transponders although the INTELSAT VI at the extreme end has 50.

TVRO
Television Receive Only terminals that use antenna reflectors and associated electronic equipment to receive and process television and audio communications via satellite. Typically small home systems.

Tweeking
The process of adjusting an electronic receiver circuit to optimize its performance.

TWT (Traveling-wave tube)
A microwave tube of special design using a broadband circuit in which a beam of electrons interacts continuously with a guided electromagnetic field to amplify microwave frequencies.

TWTA (Traveling-wave-tube amplifier)
A combination of a power supply, a modulator (for pulsed systems), and a traveling-wave tube, often packaged in a common enclosure.

Unicast
A unicast application transmits a copy of every packet to every receiver.

Uplink
The earth station used to transmit signals to a satellite.

V.35
ITU-T standard describing a synchronous, physical layer protocol used for communications between a network access device and a packet network. V.35 is most commonly used in the United States and in Europe, and is recommended for speeds up to 48 Kbit/s.

VSAT
Very small aperture terminal. Refers to small earth stations, usually in the 1.2 to 2.4 meter range. Small aperture terminals under 0.5 meters are sometimes referred to Ultra Small Aperture Terminals (USAT's).

VSWR
Voltage Standing Wave Ratio. A measurement of mismatch in a cable, waveguide, or antenna system.

Waveguide
A metallic microwave conductor, typically rectangular in shape, used to carry microwave signals into and out of microwave antennas

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