Mal,
Maybe your PC clock is not set up accurately enough or drifts
off?. It helps to regularly update the PC clock from an internet time service
provider.
www.atomic.com is free and works
for me. Mine updates every few minutes. I did see plenty of spots by you
though, so guess you may have fixed the issue already?
Perhaps
take a look for my 30uW ERP WSPR2 signal on 137.5kHz please? It will be weak,
but then you have the best system in the UK, so should be no problem for you,
or at least it would be an excellent measure of your system's performance if
you do decode me. Should be on until late tonight.