[600MRG] double reporting of strong wspr signals

[John Molnar]

Rudy, many of us have experienced the same double decodes from various
stations.

In some cases the transmitting stations DID have marginal PS filtering.

I set up a test here awhile back, monitoring myself with a completely
independent line up.  Running WSPR on my main transmitter at about 250W
out, no doubles were noted.  The PS for said transmitter is unregulated,
consisting of a 40V (AC)
100A transformer, full waved into 150,000 uF, consisting of 8 banks of
series/parallel caps.  I removed one bank at a time and doubling began with
30,000 uF remaining in the filter.

The U3 board is very susceptable to producing doubles without good solid DC
and common sense bypassing.  The creator of the U3 was not a believer in
bypass caps.

Just my observations here.

John XKA


On Tue, Mar 4, 2014 at 1:41 PM, Rudy Severns <n6lf at epud.net> wrote:

> 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
>
>
>
> _______________________________________________
> 600MRG mailing list
> 600MRG at w7ekb.com
> http://w7ekb.com/mailman/listinfo/600mrg_w7ekb.com
>