Archive | November 13, 2017

Satellite Communications Is It All That It Is Cracked Up To Be Here Are The Limitations That The E

The limitations of satellite communication systems are determined by satellite’s technical characteristics and its orbital parameters. Active communication satellite systems are limited by satellite transmitter power on the downlink frequencies and, to a lesser extent, by the satellite receiver sensitivity on the uplink frequencies.
The amount of power available in an active satellite is limited by the weight restrictions imposed on the satellite. Early communications satellites are limited to a few hundred pounds because of launch vehicle payload restraints, but now a day the weight limit is increased very much. Additionally early in efficient power cells were the only feasible power source consistent with these weight limitations. Thus the radio frequency power output was severely limited and a relatively weak signal was transmitted on the down link frequencies. Continued progresses in the development of more efficient power sources and relaxations have largely overcome these limitations.
Although powerful transmitter and highly directional antennas can be used at an earth station, the wave front of the radiated signal spreads out as it travels through space. The satellite antenna intercepts only a small amount of transmitted signal energy and because of antenna’s low gain, a relatively weak signal is received at the satellite receiver. Although the strength of the signal received on the up link frequency is not as critical as that of the signal received on the down link frequency, careful design of the radio frequency stage of satellite receivers is necessary to achieve satisfactory results.The continued development of stabilized high gain antennas and improved radio frequency input stages in the receiver will make this problem less critical.
The availability of a satellite to act as a relay between two earth terminals depends on the location of the earth terminals and on the orbital pattern of the satellite. All satellites, except those in synchronous circular orbits, will be in the mutual visibility window of any pair of earth stations only part of the time. The length of time that a non synchronous satellite in circular orbit will be in the mutual visibility window depends on the height at which the satellite is orbiting. Elliptical orbit causes the satellite zone of mutual visibility to vary from orbit to orbit, but the times of mutual visibility are predictable. Initial cost of the equipment is higher so it can be issue for some. One more thing is that for local news and announcements tuning is needed.