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Floyd Davidson wrote:
"---the look angle for a geosynchronous satellite here is about 12 degrees if the satellite is directly south." Floyd is in Alaska. Floyd`s example of anomalous propagation from reflection to a terrestial transmission was in Arizona. On the equator, the "look angle" may be nearly straight up. The reason a satellite dish is less susceptible to earth reflections is that the satellite dish is not aimed to pick the reflections up. The satellite dish is aimed at the sky. A terrestrial microwave dish aimed directly at the satellite dish is likely not transmitting an interfering frequency, but if so, it is unlikely to be aligned well enough or above the horizon of the satellite dish. The approximate specifications of a 6-foot dish for beamwidth and gain versus frequency a 1.3 GHz 9 deg. 25 dbi 2.3 GHz 5 deg. 30 dbi 3.5 GHz 4 deg. 33 dbi 6 GHz 2 deg. 36 dbi 10 GHz 1.5 deg 43 dbi 25 GHz 0.5 deg 50 dbi Sources of the above are the "RSGB VHF-UHF Manual" and the ARRL Antenna book (they agree). In moderate latitudes, the satellite earth station antenna is really looking up. It is quite likely terrestrial signals are not within range of its bandwidth, beamwidth, or distance. Best regards, Richard Harrison, KB5WZI |
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