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A radio wave transmitted from an earth station (ground-based station) is attenuated (weakened) as it travels farther from the station before reaching a communications satellite. The communications satellite amplifies the attenuated radio wave and retransmits it to another earth station.To prevent radio interference, the uplink (transmission to the satellite) and the downlink (transmission to the ground) use different frequencies.
The communications satellite appear stationary in the sky as it orbits the earth 36,000 km above the equator in the same cycle as the rotation of the earth. It is therefore called a geostationary satellite.
