The basic difference is that optical fibers transmit

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Unformatted text preview: unted on the satellite amplifies the weak signal and transmits it back to the earth at a frequency of 4 GHz or 1 lGHz. This signal is received at receiving station on the earth. It may be noted that the retransmission frequency is different from the transmission frequency in order to avoid the interference of the powerful retransmission signal with the weak incoming signal. A transponder can typically support 1200 voice channels each of 4800 bps or 400 digital channels each of 64Kbps data transmission rate. A satellite has many transponders. Therefore, a single satellite has enormous data communication capability. The use of 4 GHz band of frequencies for transmission and retransmission of microwave signals in a satellite communication system is called the C-band transmission. On the other hand, the use of 11 GHz to 14 GHz band of frequencies is called the Ku-band transmission. In order that a large number of users can benefit from satellite communication, it was realized that the size and cost of the receive-transmit earth stations has to be considerably reduced so that one can easily install a private earth station. To meet this requirement, smaller dish antennas having lower power transmitters and receivers have been built for installation at users' sites. These dish antenna systems are popularly known as VSATs (Very Small Aperture Terminals). The aperture refers to the diameter of the dish antenna, which is about 1 to 2 meters. Satellite communication systems have the following advantages: 1. A satellite, which is essentially a microwave relay station visible from any point of a very large area, can be used for transmission and reception of data between any two randomly chosen points in that area. 2. Data transmission costs are independent of the distance between two points as long as the two points are within the area covered by the satellite. 3. A satellite having many transponders has enormous data communication capability. 4. Error detection is trivial in a satellite...
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