A wireless communication that uses a satellite placed in an Orbit around the earth for a long distance communication of signals to different parts of the world is known as ‘communication satellite’.
Just as various planets revolve around the sun, in the same way few celestial bodies revolve around these planets. These bodies are called satellites. For example, moon revolves around the earth in a nearly circular orbit. What is a planet and moon is a satellite on the earth. When a satellite revolves around the earth in an Orbit near the Earth's surface then its orbital velocity is about 8 km per second. Therefore if we send a body a few hundred km above the Earth's surface and give it a horizontal velocity of 8 km per second by means of a multistage rocket, then the body is placed in an Orbit around the earth. Such a body is called an artificial satellite.
If an artificial satellite be placed in and Earth's Orbit in the equatorial plane at a height of 35830 KM above the surface of the Earth, then its period of revolution around the earth would be exactly equal to the period of axial rotation of earth, that is, 24 hours. The satellite would then appear stationery over a point on Earth's equator. Search a satellite is known as “geostationary satellite”, and its orbit is known as ‘synchronous satellite’. If this satellite carries receiver and transmitter, then it can be used to receive TV and telephonic signals from one part of the world and transport them to different parts of cross the group. This is satellite communication.
There are two types of satellites used for long distance communication :
The satellite which carries all the equipments used for receiving wireless signals sent from earth, processing them, and then retransmitting them to the earth is called active satellite.
The satellite which is used only as a reflector of the signals transmitted from earth is called passive satellite.
Applications/Uses of Satellite
Navigation satellites can be used for a number of purposes. Some of them Are the following :
- Television Distribution : programs are transmitted to the satellite and then broadcast down to a number of stations which distribute the programs to individual viewers.
- Long distance telephone transmission : satellite transmission is also used for point-to-point trunks between Public Telephone Exchange offices.
- Business networks : the satellite divides the total business data of a network into a number of channels and lease these channels to individual businessmen.