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Re: LF: 500kHz 1mW WSPR beaconing

To: [email protected]
Subject: Re: LF: 500kHz 1mW WSPR beaconing
From: Andy Talbot <[email protected]>
Date: Sun, 25 Oct 2009 20:42:13 +0000
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There is no 'chance' involved.  The strong source coding employed in all the WSJT modes to get the number of bits to be encoded down to an absolute minimum, before proper error correction is added, removes all wasted redundancy in the original callsign format.   This has the result that most truly random bit patterns will therefore generate a valid looking callsign.  Its an artefact of efficient coding.
 
That this only happens occasionally is due to the strong properly constructed error correction that is subsequently added.  
 
 BUT    As the callsign is not encoded in the most efficient way it could possibly be (which would be a codebook of all the radio-ams in the world  = 1 million perhaps with a 20 bit reference number) we identify an invalid callsign by experience, and by correlating with known propagation / locator facts.  
 
Information theory is a wonderful study - and being able to be put into practice more easily with cheap processing power than it ever was before.   I'll be covering this, amongst other aspects of weak signalling, at the Martlesham Microwave Roundtable.  http://mmrt.homedns.org/start.html   (talk entitled 6dB better than CW.)

Andy
www.g4jnt.com

this email has been scanned for political correctness by the nanny state


2009/10/24 Graham <[email protected]>
Roger
 
This happened ..
 
G ,,
 
Timestamp Call MHz SNR Drift Grid Pwr Reporter RGrid km az
 2009-10-24 16:58   G3XBM   0.503917   -28   0   JO02dg   0.001   G0NBD   IO83   261   302 

Sent: Saturday, October 24, 2009 4:55 PM
Subject: LF: 500kHz 1mW WSPR beaconing

This will be active periodically over the weekend. It would be nice to get a few new reporters spotting me.

73s
Roger G3XBM

--
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G3XBM    GQRP 1678      ISWL G11088



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