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Re: LF: RE: WSPR Reports

To: [email protected]
Subject: Re: LF: RE: WSPR Reports
From: Andy Talbot <[email protected]>
Date: Wed, 27 Jan 2010 21:50:46 +0000
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Yes, as Paul suggests, it does look as if AGC is the culprit.   Narrowing the Rx bandwidth right down to 7Hz won't make any difference to decoding ability provided there is no AGC pumping from out of (WSPR band) signals.   
 
(But any bandwidth selected below 7Hz will then knock out tone energy in the two outside ones).
2010/1/27 Clemens Paul <[email protected]>
This phenomen,or rather bug,has been reported here by several list members.
I have made the same observations.
Reducing the RX BW from e.g. 250Hz to something below 100Hz results in
an increase of *reported* SNR of up to around 15dB!
I've done some tests with a friend 20km away on 10m and we've found out that the *real* SNR
is not improved a bit or in other words an extreme weak wspr signal which was just below
the decoding threshold in 250Hz BW coudn't be decoded with 20Hz BW either.
 
73
Clemens
DL4RAJ
 
----- Original Message -----
Sent: Wednesday, January 27, 2010 9:44 PM
Subject: Re: LF: RE: WSPR Reports

All the critical filtering is done in the software, and results in a 1.46Hz noise bandwidth - which is what the software measures and reports upon.
 
Your observation that a narrower IF bandwidth is interesting.   Its most likely based on the fact that typical signals are corrupted by pulsed non-gaussian noise which upsets the frequency bin detection process, and upsets sync recovery.
 

Andy
www.g4jnt.com

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2010/1/27 Rik Strobbe <[email protected]>
Andy,
 
maybe the "magic" lies in a narrow filter (either IF or audio).
If I switch from a 2.5kHz (SSB) filter to a 270 Hz filter I also get a significant increase in SNR values reported by WSPR.
Unfortunaely it hardly affects the decoding level (minimal SNR needed to get a positive decode), that rises by almost the same amount.
 
73, Rik  ON7YD - OR7T

Van: [email protected] [[email protected]] namens Andy Talbot [[email protected]]
Verzonden: woensdag 27 januari 2010 21:26
Aan: [email protected]
Onderwerp: LF: WSPR Reports

Has F6CNI managed some sort of magic noise reduction system, or is it a just a case of being in a very quiet location...
These are pretty impressive S/N values
 
 
 2010-01-27 20:14   G4JNT   0.503875   +13   0   IO90iv   +23   0.200   F6CNI   JN19qb   391   243 
 2010-01-27 20:08   G4JNT   0.503875   +10   0   IO90iv   +23   0.200   F6CNI   JN19qb   391   243 
 2010-01-27 20:02   PA0A   0.503900   +15   0   JO33de   +37   5.012   F6CNI   JN19qb   502   312 
 2010-01-27 20:00   G4JNT   0.503875   +14   0   IO90iv   +23   0.200   F6CNI   JN19qb   391   243 
 2010-01-27 19:54   G7NKS   0.503920   -5   0   IO92ub   +20   0.100   F6CNI   JN19qb   422   262 
 2010-01-27 19:54   G4JNT   0.503875   +14   0   IO90iv   +23   0.200   F6CNI   JN19qb   391   243 
 2010-01-27 19:44   G4JNT   0.503875   +10   0   IO90iv   +23   0.200   F6CNI   JN19qb   391   243 
 2010-01-27 19:40   PA0A   0.503900   +15   0   JO33de   +37   5.012   F6CNI   JN19qb   502   312 
 



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