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Africa satellite internet service providers |
Example link budget Europe to Africa |
Eutelsat W3A satellite Africa beam coverages.
Downlink beam contours EIRP, in units of dBW.
Downlink beam contours are in dBW and refer to the full transponder power when used with a single carrier. If you are operating a small carrier in a transponder carrying many carriers then note that the total composite power will be several dB lower due to the transponder being operated backed off to achieve an appropriate level of intermodulation interference. Your satellite EIRP power will approximate to your fair share of the total, according to your bandwidth.
The downlink contours help to determine your receive dish size.
Uplink beam contours G/T in units of dB/K
The uplink beam contours show the input quality of the satellite in dB/K. The sensitivity of the satellite is expressed in units of power flux density at the satellite to cause the transponder output to saturate. PFDsat in units of dBw/M^2. The sensitivity may be adjusted using an adjustable attenuator on the satellite and you need to find this value for your particular transponder before doing your link budget. The higher the sensitivity setting the less uplink power you will need from your earth station, but the lower power will reduce you uplink C/N ratio, you will also make your uplink signals suffer more from interference. A low gain setting will require more uplink power and enable you to achieve a high uplink C/N and less susceptibility to interference. A large uplink dish is preferred to minimise interference caused by your high spectral density carrier to the opposite polarisation transponder and nearby satellites.
The uplink contours help you determine your uplink dish size and transmitter BUC power. A
-3dB reduction means a dish of twice the area or 1.4 times the diameter or BUC of twice the power rating (watts).
G/T is gain to noise temperature ratio. Gain refers to the satellite receive beam gain. A small spot beam will have a high gain, a broad continental beam, like that above, will have a low gain. A global coverage beam has the lowest gain since it is approx 17 degrees diameter in order to view all of the visible earth, as seen from geostationary height. See these satellite views. Noise temperature refers to the system noise temperature at the input to the satellite receiver. It comprises the noise of the satellite receive LNA plus a major contribution from the warm earth (270K) towards which the satellite antenna is pointed. The sea looks cooler since it reflects cold space.
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Page started 11 Feb 2010, amended 10 July 2020. ECJ |