Hi Dave, LF,
> Dave Sergeant wrote:
>> 3. You are of course s9+ at this range, and show as bright red on WSPR's
>> spectrogram. Hardly 'weak signal'. Does the software cope with strong
>> signals or does it overload?
I get about 25% decode from Graham G0NBD who is about 35-40 miles from
me, all weaker signals decode OK. As it is a weak signal mode the
stronger signals must be a cause of non-decodes.
73,
Gary - G4WGT.
2009/9/5 John P-G <[email protected]>:
> Dave, LF,
>
>
> Dave Sergeant wrote:
>
>>
>> Well prompted by all the mails on here I have just installed the WSPR
>> software and had a listen to your signals this morning.
>>
>> I noticed a couple of things which might explain why I was not getting any
>> decodes:
>>
>> 1. On switch on of my K2 and Datong UC1 which I use for 500kHz receive
>> there is a noticeable drift, initially as high as 10Hz in the 2 minute
>> sampling period but eventually dropping to within 1Hz. I could not find a
>> spec as to how stable the receiver needs to be for WSPR. I believe most of
>> this drift is the 116MHz downconverter crystal in the UC1, which is a big
>> limitation to using it as a serious 500kHz receiver.
>
> The frequency needs to be reasonably stable - the WSPR software will report
> the frequency shift seen during a reception period as "Drift" and I've seen
> a few reports of 1 or 2 Hz. This implies that it will work with a 1-2Hz
> drift across the 2 minute period. I'm not sure what the absolute limit is
> though.
>
>> 2. Although I synchronised my computer clock to the time standards, and it
>> seems just a fraction of a second different from my 60kHz clock, your
>> transmissions seemed to be starting a second or two early, before my WSPR
>> started receiving, and finishing at around the 1.52 minutes point. Is your
>> clock out, or is this how it is supposed to work?
>
> My PC is running NTP and is (hopefully fairly well locked to NTP time) and
> WSPR reports "DT" (Delta Time) of +/- 0.1 Seconds on Jim's signals, so I
> guess that he and I are in agreement of what the correct time is, and he's
> getting lots of spots reported from other stations, so I don't think his
> timing is an issue. His trace on the waterfall in WSPR sits nicely in the
> 2-minute window.
>
> I've seen successful decodes with DTs of up to 2 seconds.
>
> The SNR/clock rate issue (see below) might muddy the waters on absolute
> timing accuracy though?
>
>> 3. You are of course s9+ at this range, and show as bright red on WSPR's
>> spectrogram. Hardly 'weak signal'. Does the software cope with strong
>> signals or does it overload?
>
> This might be significant though.
>
> I've seen may times that very strong signals fail to decode whereas much
> weaker ones from the same station (eg during QSB or after reduction in TX
> power) decode fine. There is one theory that it's to do with the accuracy of
> the soundcard clocks. With weakish signals some of the transmission is lost
> in the noise and the FEC will kick in and allow a decode by "filling in the
> gaps". With very strong signals no data is missed, and due to clock rate
> differnces the decode fails because the received bits are outide the
> tolerance of the decoder, timewise (A very poor description, sorry - Andy
> JNT will explain better).
>
>
> This could imply that either yours or Jim's soundcard is not up to the job.
> Since Jim has had spots reported from close stations with SNRs of +9dB I
> guess this implies Jim's timing must be okay. I've seen this effect kick in
> when signals start to go into the positive SNR region.
>
>
>> The only decode I got was for 'C1N/NU0RWS' in one of your non-transmit
>> periods.
>
> That's a false decode and might indicate that you have a noise problem. I've
> seen similar gobbledegook decodes from people with high noise levels.
>
> HTH
>
> I'm receiving Jim consistently, in daylight, at -21dB SNR at 953km distance
> - on a Wellbrook ALA1530 loop.
>
>
> Cheers,
>
> John
>
>
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