----- Original Message -----

From: Andy Talbot

To: [email protected]

Cc: [email protected]

Sent: Sunday, February 07, 2010 7:20 PM

Subject: LF: WSPR S/N Tests

To try to get to grips with the falsely high values of  S/N reported by some stations recently, I made a set of controlled measurements over a direct link using a range of Rx bandwidths and input signal levels.

 

The results were dramatic.  With receive bandwidths less than 300Hz, the reported S/N increased considerably.   It was only possible to use bandwidths in steps of 500Hz so 100,150,200 etc with the SDR-IQ but these were more than enough to show the effect.

 

Full details can be found in www.g4jnt.com/WSPR_SNR_Test.pdf  but the results can be summarised as :

 

-------------   Don't use a bandwidth below 300Hz unless you want artificially high SNR reports    -----------------------

 

300Hz or anything higher that allows the decoding software to see the full noise band is OK.

Andy
www.g4jnt.com

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