That Douple Peak...

John, EI7GL, raised a question yesterday as to the cause of an apparent 'double peak' in 14MHz WSPR signals received from VK3MO and QN (operated by the same person).

This graph is very typical of what happens in the morning in Wales:

I used VOACAP to predict the signal strength for both long and short path.  The standard input parameters to this can't hope to accommodate the type of vast arrays that Ian is using, but an 8-element Yagi beaming LP Europe at maximum height is used, together with CW-equivalent output of about 1kW, to approximate the WSPR reality.

I think the results, within the constraints of VOACAP's once-per-hour computations, confirm very nicely that the first peak is the result of the short path. This (purple, 14MHz) peak is predicted to be - and is often confirmed in practice - slightly weaker and broader than the second peak, which comes ~40 minutes later, and is the result of a switch to long path (probably still with some influence from short path).

Short path signal strength prediction, VK3 to Wales.

Long path signal strength prediction, VK3 to Wales.

Turning to Proppy's output on area coverage, again assuming a large Yagi array and LP Europe heading from VK3 (this time, using ~25W FT8), it becomes quite evident as to how complex the various paths from VK to Wales are at the moment:

This is my best attempt at understanding the situation.  Maybe you have a different analysis, in which case, I'd be only too happy to learn about it, if you leave a comment, below.