Lab 5

Explain in brief the Citizens’ Band Radio (CB)? It is Cellular Radiotelephone system using of half-duplex (push-to-talk) operation for CB radio. It needs only one channel per conversation, and using AM (including its narrower bandwidth variant, SSB).

What are the main disadvantages of the CB radio? Lack of privacy and co-channel interference are major problems The low frequency, which requires antennas to be large if they are to be efficient, is also a problem for portable transceivers

Under what circumstances would you use GEO, LEO, and MEO satellites, respectively? You would use GEOs when the earth stations are not near the poles, when there is a premium on not having to steer the earth station antennas, and when broad earth coverage is important, for television broadcasting for instance. HEOs are primarily of use when coverage of areas near one of the poles is essential, such as the use of the Molniya satellites to cover the northern parts of the former Soviet Union. LEOs are useful for point-to-point communication, and for extensive frequency reuse. Since LEOs have much less propagation delay, they are useful for interactive data services. They also can cover Polar Regions. Finally, while you need many more LEOs for broad coverage, each satellite is much less expensive than a GEO.

What are three key factors related to satellite communications performance? (1) Distance between earth station antenna and satellite antenna. (2) In the case of the downlink, terrestrial distance between earth station antenna and the "aim point" of the satellite. (3) Atmospheric attenuation.

What are three factors that limit the number of subchannels that can be provided within a satellite channel via FDMA? Thermal noise, intermodulation noise, and crosstalk