communication satellite

Communication Satellite

communication satellite are microwave relay stations in outer space. A space shuttle launches a satellite and place it in outer space precisely 36,000 km above the equator with an orbit speed that matches earth's rotation speed exactly. Being in geosynchronous orbit, a satellite is stationary relative to the earth and always stay over the same point on the ground.This allows a ground station to aim its antenna at a fixed point in the sky.Each satellite can receive and re transmit signals to slightly less than half the earth's surface because the earth is round.
In satellite communication, microwave signals at 6 GHz or 14 GHz (1 GHz = 10 to power 9 Hz) is transmitted from a transmitter on earth to a satellite positioned in space .By this time this signal reaches the satellite, it becomes due to 36,000 km travel.A transponder mounted on the satellite, amplifies the weak signal and transmit it back to earth at a frequency of  4 GHz or 11 GHz. A receiving station on the earth receives this signal. Re transmission  frequency is different from transmission frequency to avoid interface of powerful transmission  signal with weak incoming signal.
A transponder can support typically 1200 voice channels each of 4800 bps, or 400 digital channels each of 64 Kbps(kilo bit per second). A satellite has many transponders.Therefore, a single satellite has enormous data communication capability.
Use of 4 GHz to 6 GHz band of frequencies for transmission and re transmission of microwave signals in a satellite communication system is called C-band transmission, and use of 11 GHz to 14 GHz band of frequencies is called Ku-band transmission.