r to explore, we realize that although fiber may be the best solution on the planet, when we want to advance in space, satellite communication is extremely important. Frequency Allocations of Satellite The frequency spectrum in which most satellites operate is the microwave fre- quency spectrum. (GPS runs at VHF frequencies and is a very important applica- tion.) Therefore, microwave and satellite signals are really the same thing. The difference is that with satellite, the repeaters for augmenting the signals are placed on platforms that reside in high orbit rather than on terrestrial towers. Of course, this means that the power levels associated with satellite communications are greater than those of terrestrial microwave networks. The actual power required depends on the orbit the satellite operates in (geosynchronous-orbit satellites Chapter 2 Traditional Transmission Media require the most power, and low-earth-orbit satellites require the least), as well as the size of the dish on the ground. If the satellite has a lot of power, you don't need as big a dish on the ground. This is particularly important for satellite TV, where the dish size should be 2 feet (0.6 m) or smaller. A number of factors are involved in the bandwidth availability of satellite: what spectrum the regulatory agencies have allocated for use within the nation, the portion of the frequency spectrum in which you're actually operating, and the number of transponders you have on the satellite. The transponder is the key communications component in satellite. It accepts the signal coming from the earth station and then shifts that signal to another frequency. When the signal is on the new frequency, it is amplified and rebroadcast downlink. In satellite communications, the frequency allocations always specify two dif- ferent bands: One is used for the uplink from earth station to satellite and one for the downlink from satellite to earth station. Many different bands are specified in the various satellite standards, but the most dominant frequ