Case study 2
It is desired to use Optus satellites at 156 and 160 degrees to transmit different services to an earth station in Canberra . Does a 0.7 m antenna have enough discrimination to receive the signals without interference? Perform the calculations for 1.5 GHz, 12.5 GHz and 30 GHz. Assume both satellites produce equal EIRP levels at the Canberra receiving site.
Solution 2
It can be shown that
(1) assuming
55% efficiency
FM television requires a protection ratio of about 30 dB to avoid interference. So with 0.7 m dishes the service would nearly operate without interference at 30 GHz but would certainly suffer interference at 12.5 and 1.5 GHz. Under these conditions services intended for 0.7 m dishes cannot be transmitted at the same time on both satellites.
If digital modulation is used less protection ratio would be required.
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