More often than not, the parallel traces on strong(ish) signals is due to overload in the computer's soundcard. Easily repeatable.[/quote]VK3DXE wrote:The freq difference is 36Hz, same callsign... so it looks like the same tx being recieved by two paths with some relative Doppler shift. 36Hz is not a large Doppler shift at that freq.
The quite small change in the Doppler on each signal might be explained by two aircraft travelling the parallel lanes and about the same position along the path to give similar but opposite shifts.
If you watch the Flightradar, you might find scenarios where that might happen, and observe what you see on WSPR (if someone in the right place is transmitting that interval).
Leigh shows a similar observation in a post just prior to this.
Owen
Did you look at the pics? Are you saying you think it is receiver IMD?
Doesn't look like it to me... one signal fades up as the other fades down... enough reason to not be IMD.
Owen