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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
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.
A satellite having many transponders has enormous data communication
4. Error detection is trivial in a satellite...
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- Spring '14