JEE Main & Advanced Physics Communication System / संचार तंत्र Satellite Communication

(1) Satellite communication is like the line-of-sight microwave transmission. In this case, a beam of modulated microwave is projected towards the satellite.

(2) Satellite communication is mainly done through geostationary satellites (for steady reliable transmission and reception)

(3) A geostationary satellite has the same time period of revolution of earth (i.e. 24 hrs.). It appears stationary w.r.t. earth. It locates at the height of 36000 km above the earth's surface (well above the ionosphere).

(4) A communication satellite is a spacecraft placed in an orbit around the earth which carriers a transmitting and receiving equipment called radio transponder. It amplifies the microwave signals emitted by the transmitter from the surface of earth and send then to the receiving station on earth.

(5) The transmitted signal is UP-LINKED and received by the satellite station which DOWN-LINKS it with the ground station through it's transmitter.

The up-link and down-link frequencies are kept different (both frequencies being in the regions of UHF/microwave).

(6) A single satellite cannot cover the entire surface of the earth. At least three geo-stationary satellites are required which are 120° apart from each other to have the communication link over the entire globe of earth.

(7) Satellite technology is very useful in collecting information about various factors of the atmosphere which governs the weather and climatic conditions.

The satellite communication can be used for establishing mobile communication with great use the communication satellites are now being used in Global Positioning System (GPS). The ordinary users can find their positions within an accuracy of 100m.

There are two types of satellites used for long distance transmission.

(i) Passive satellite : It act as reflector only for the signals transmitted from earth. Moon the natural satellite of earth is a passive satellite.

(ii) Active satellite : It carries all the equipment used for receiving signals sent from the earth, processing them and then re-transmitting them to the earth. Now a days active satellites are in use.

(8) The Indian communication satellites INSAT-2B and INSAT-2C are positioned in such away in the outer space that they are accessible from any place in India.