Would anybody be interested in exploring signal path reciprocity for shortwave communication? Or rather changes in reciprocity over time. It sometimes happens that for a period of time the path to a distant station seems to be more or less unidirectional. And I’m not talking about different noise levels but actual signal level.
The ionised plasma together with the Earth’s magnetic field will twist and deflect radio waves travelling through it making the path more or less non reciprocal.
I’ve been using WSPR to measure the reciprocity between SM and North America and it indicates that there at times could be a difference of up to 10 dBs. But there is a problem using WSPR. The output is not signal strength but SNR. On higher bands the QRN level is fairly constant over time, if not beaming into the sun, but there could be local noise or sudden QRM from say RTTY stations. At my end I’ve solved that by listening to a local station some tenths of km away and using that signal as a reference (the difference over a 24 hour period was very little). The DX station though did not use that feature.
The means of measuring the reciprocity is open to discussion.