Advertisements
Introduction To Satellite Communication
"The process of sending information around the world has been revolutionized by the advent of satellites. The Telestar, Syncom and Early bird satellites have demonstrated the feasibility of wideband communication over large distances. A good quality service can be continuously obtained by a global operational satellite system".
High frequency radio and submarine cable systems are widely used for long distance overseas telecommunications. The H.F. band from 3 MHz to 30 MHz, has provided worldwide telephone and telegraph circuits, but is subject to - drawbacks of high noise levels and limited bandwidth.
Since ionospheric reflection is not possible for frequencies in the V.H.F. and microwave bands, line of sight links are required with an array of repeaters. The advent of artificial earth satellites provides a microwave repeater at almost any desired altitude so that distances of thousands of kilometers can be covered by a single earth-satellite-earth link.
Satellites presently in use are active satellites, i.e. the signal received by the satellite is retransmitted rather than being simply reflected back to the earth. This means that satellite has on-board, highly directional transmitting and receiving antennas, and complex interconnecting circuits. Accurate positioning and control mechanisms are required for the satellite. The power requirements for the on-board equipment are obtained from arrays of solar cells, with back- up nickel-cadmium batteries for periods of solar eclipse.
With the establishment of INTEL SAT (International Telecommunication Satellite Consortium) on 20th August 1964, the communications by means of satellites was stressed. The use of geo-stationary satellites for domestic communications was found attractive to large, countries. The India's first multipurpose domestic communication satel1ite INSAT (Indian National Satellite) was operational in 1981.
The satellites were placed in geo-stationary orbit at 74-degree east longitude employing 6GHz frequency band. Thereafter INSATIA, INSATIB, INSAT IC & INSAT 2A were operational. Arianespace from French Guyana launched the INBAT 2B on July 23, 1993. The INSAT 2C was launched in 1995. This is purely a communication satellite. These satellites normally measure about 2.2 metres in height, and between 4 to 6 metres between its solar panel, weighing around 900kg. These are used for tele-communication meteorology and nationwide T.V look-tip.
