20 Jul 2014

Doppler on local and GDX 10m and 6m signals

G0LRD has already shown that what I have described as Doppler on 6m is, sometimes, the drift as my FT817 goes from TX to RX and cools down. Certainly some WSPR signals are affected by aircraft reflections, evidenced by multiple traces. It is an open question whether or not some signals are only propagated at decent GDX distances as a result of aircraft or whether it is just the tropo signal that is decoded. My strong suspicion is that at least some GDX is only possible when planes are in the right orientation and Doppler shift is low enough to allow a successful decode.

Notice the (additional), aircraft reflected, signal from G0LRD ((above 100) earlier. Clearly the decode was on the flat trace coming directly and not that coming via a plane. Sometimes I have seen as many as 6 aircraft reflections. The traces lower in frequency did not decode as the Doppler was too great. Doppler on 6m is worse.

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