satellite

Satellites are transponders unit that receive on one Frequency and retransmit on another that are set in  geostationery orbits directly over equator. This stationery orbits are 36,000 km away from the earth's surface.At this point,the gravitational pull of the Earth and the centrifugal force of Earth's rotation are balanced and cancel each other out.Centrifugal force is the rotational force placed on the satellite that wants to fling it out into space.The uplink is the transmitter of data to the satellite.The downlink is the receiver of data.Uplinks and down links are also called Earth stations because they are located on the Earth.The footprint is the "shadow" that the satellite can transmit to,the shadow being the area that can receive the satellite's transmitted signal.Communications Satellite rotates at almost exactly the same rate as the earth rotate.Compared to the radio link,the satellite has a considerable large range.They are used for both in the national network and in the international network.There are only a few problems in the transmission characteristics of the satellite link.