Some of the activity here at the weekend was devoted to attempting to get some signal by any means to SWLGM Mark in Edinburgh. Very little signal was seen from either G6AVK or G3ZJO on Marks 6m Zepp antenna.
The use of WSPR gave the chance to look for Aircraft Reflections which produce a double de-coded report. There were several examples spotted and screen grabs taken of them. I am still not certain of the distance involved to the reflecting plane. Currently I think it is quite large c.500kM.
A most interesting de-code came late in the day. A double de-code of my signal at G6AVK.
This shows only 1dB less signal strength for the reflection compared to the 'direct' path and a 51Hz shift.
Luckily G6AVK also captured the WSPR Waterfall and better still a Spectrum display.
The top trace is the Direct Path signal, 51Hz below is the Reflection which de-coded, clearly many dB lower than the Direct.
Between these two is a curving reflection, stronger than the direct signal, this type of signal has never been seen here to decode the WSPR data.
After some thought I can offer an explanation of the mechanism involved. I am quite happy to listen to alternatives.
The trace 51Hz below the top direct path one produced the de-code, it come from an Aircraft flying North in the North UK Air Lane.
The curving trace comes from a much closer (to G6AVK) Aircraft, joining the South South East Air Lane (off to the South of France) and reaching a cruising speed very close to that of the Aircraft travelling North. Using standard speeds in a control area is the way that Aircraft are kept apart. Reaching the right place at the right time is a game of chance, we had been playing roulette all day.
So is the alignment of G3ZJO G6AVK and The SSE Air Corridor a possibility, yes this is only a rough layout on the map.
Right click and select View Image for full size.
So finally why the odd report of signal level from WSPR. I believe that the signal from the closer Aircraft to the south swamped or reinforced the complete reflection, the de-coder giving an average strength reading over the whole period. Joe?
