Communication satellites work by sending signals and transmissions down to Earth stronger than the signals received by the satellites. These Earth-orbiting devices convert transmissions from one frequency to another, so signals are not confused between transmission and reception. Communications satellites contain antennas, transponders, power sources and propulsion systems.
Communications between ground stations and orbiting satellites operate between 1 gigahertz, or GHz, up to 50 GHz. Frequency bands are identified by various letters, including L-, S-, C-, X-, Ku-, Ka-, and V-bands, in ascending order of frequency. Lower-frequency satellites require larger equipment to locate transmissions in orbit and higher-transmission communications satellites have smaller antennae. Ku- and Ka-band satellites send signals to Earth for digital communications, broadband applications, and direct-to-home transmissions.
Communications satellites decrease in size as technology improves. As of August 2014, the smallest versions of these devices are less than 2.2 pounds, while the largest communications satellites are more than 14,000 pounds. Early forms transmitted just one signal at a time with one transponder. The largest satellites contain hundreds of transponders with 16 channels each, for 1,600 television channels transmitted through a single satellite.
A transmission completes in three steps: a communication station on Earth transmits, or uplinks, a signal to a satellite; the satellite then increases the strength of the signal and sends the transmission, or downlinks, to Earth; finally, the signal arrives at the receiving station at a far-away location on the surface.