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Re: LF: More EbNaut 137.777

To: [email protected]
Subject: Re: LF: More EbNaut 137.777
From: Paul Nicholson <[email protected]>
Date: Sun, 29 Nov 2015 23:30:03 +0000
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VO1NA 2015-11-29 8K19A 2S 5C

 20:00  6.2 dB
 20:30  7.0 dB
 21:00  3.2 dB
 21:30  1.4 dB
 22:00  5.4 dB
 22:30  no decode
 23:00  8.7 dB

Edgar wrote:

> I had been looking at vtmatch.

vtmatch monitors a stream and does a continuous
cross correlation against the template: in other
words a matched filter.

It would be the one to use if you knew what the
message was but not the start times.

Generate a template file for vtmatch with

 echo 'TNX PAUL' |
   ebnaut -e -r100 -S2 -p8K19A -N8 |
   awk '{print $1}' > ref.dat

Here, I've dropped to sample rate 100.

I should then be able to do something like

 vtread -T2015-11-28_20:00,+8h /raw | # Get 8 hours of signal
    vtfilter -h bp,f=2777,w=2 |
    vtmult -f 2777 |     # Mix 137777 to baseband
    vtresample -r 100 |  # Baseband I/Q at 100 samples/sec
    vtmatch -t ref.dat > match.vt

Then

  vtplot match.vt

should show a good spike whenever the message appears in that 8
hour stream.  The spike should be surrounded by auto-correlation
'sidebands' which ought to be quite low compared to the peak.
For some reason it's not quite working, getting the sidebands
but no central spike, even on a simulated signal.  Maybe I'm
too tired or there's a bug in vtmatch.  I'll look at it again
tomorrow.

--
Paul Nicholson
--

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