[600MRG] double reporting of strong wspr signals

[Rudy Severns]

I have a bit of a mystery that someone might be able to shed light on.  Some 
time back XSH/26 pointed out to me that he was getting two reports in the 
same time slot for my wspr signals.   Last night Neil, XSV, was very strong 
here and I generated double reports on him through the night.  He asked me 
about this and I told him the following:

      2014-03-04 13:42   WG2XSV   0.475625   -26   0   DN41ac   1 
WD2XSH/20   CN83lu   958   292
       2014-03-04 13:42   WG2XSV   0.475745   -10   0   DN41ac   1 
WD2XSH/20   CN83lu   958   292


Hi Neil,  here is an example of a double decode of your signal.  Notice that 
there are two frequencies 120 Hz apart.  The strong signal is on your normal 
frequency but the weaker one is 120 Hz lower.  Since your signal was very 
strong last night one of those signals may be a sideband introduced by 120 
Hz ripple from your power supply.  There were many of these double decodes 
and almost always the second signal is -16 dB and 120 Hz different.  That's 
just a guess.

Now to cast some cold water on that explanation,  I got a similar report 
from XSH/26 who is relatively close to me so I have +dB snr's at his place. 
I quickly slapped my HP spectrum analyzer on my signal and sure enough there 
were AC ripple sidebands, but in my case they were -60 dB down from the 
carrier which is pretty good considering I have a 55 dB gain amplifier.  I 
keep a very close eye on my signal quality so this did not explain the 
double reports?????

The other explanation would be something going on at the receiver end but 
what I have no clue???

73, Rudy