Message-ID: <497EE52C.4050808@sighthound.demon.co.uk>
Date: Tue, 27 Jan 2009 10:42:52 +0000
From: John P-G <gm4slv@sighthound.demon.co.uk>
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Subject: Re: LF: G0NBD difficult to decode
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mal hamilton wrote:
> Johan
> I have mentioned this several times before but noone seems to know why 
> strong signals or any visible signals do not DECODE. I get some decodes 
> therefore I know my system is working but not sure whether the problem is at 
> the TX or RX end. To me wspr seems unreliable given the strength of signals 
> but producing only marginal decoded output.
> 73 de mal/gkev
> 


Mal, LF,

In general WSPR is very good at decoding weak signals - that's what it's
all about after all - and can give reliable decodes on signals that are
inaudible and only faintly visible on the waterfall. Occasionally there
seem to be certain strong signals that won't decode, when weaker signals
from the same stations are fine.

Some discussion has taken place on the WSPR forum over incompatible
soundcard sampling rates, others on HF have seem the same "won't decode
strong signals" problems too.

In the current case, with G0NBD, I guess the problem, whatever it is, is
  at the sending end, as similarly strong signals from others (M0BMU and
G4JNT) decoded fine here, and elsewhere, yet many people had trouble
with G0NBD's signal.

I see that Chris G3XVL often reports a +13dB s/n ratio for Jim's signal,
which shows that strong signals can decode correctly.


The question of brevity in passing information (ie "having a QSO") is
moot - it's not really intended for that purpose. It's point is to allow
monitoring of the path conditions, using low power "weak signals" - WSPR
stands for "Weaks Signal Propagation Reporting". If you want a mode for
conveying information and exchanging reports then there's a whole gamut
- not least among them good old CW.

WPSR allows the collection, automatically, of data showing the changes
in path conditions over time, with a centralised online database of the
results, allowing others to do whatever number crunching they care to on
the data. For this the mode is perfectly valid, and given low enough
transmit power from the stations involved it shouldn't cause too many
problems for other band users. Last night's results showed that, for
inter-G (even up to Shetland) the ERPs involved were too high. Gary,
with his 5W TX and 2mW ERP is showing the way it should be done - and
that wouldn't cause too much QRM for those seeking CW QSOs elsewhere on
the band.

Using WSPR on 160m recently I discovered that I have a regular opening
to N6TTO on the west coast of USA, and I'm often the only Eu station to
receive him. Relying on more traditional modes I'd probably never have
discovered this. It means that perhaps my location is suitable for 160m,
and might be worth some investment in time/effort to get on the band.
Without the research using WSPR I'd have not realised that my location
was special - although my low noise floor has already proved its worth
on 500kHz.

Just a few thoughts from here.

Cheers,

John
GM4SLV