To: rsgb_lf_group@blacksheep.org
References: <CA+DS1VLHrmxgyHtRu8t3M13+CmcnLmgCToCYePH1TvVUrRjzEA@mail.gmail.com>
From: Paul Nicholson <vlf0403@abelian.org>
Message-ID: <acd3ab1d-6fa7-d02d-8fdb-78b26884ea86@abelian.org>
Date: Sat, 30 Dec 2017 09:42:00 +0000
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Subject: Re: LF: 8269.9 kHz EbNaut 29/12/17
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Dex wrote:

 > 8269.9 kHz
 > repeat message
 > 3 chars 16K21A CRC20
 > 30 second symbols
 > Start 22:30 UT

8269.9 Hz !

Signal extraction: vtread -T 2017-12-XX_22:30,+27900 /raw
Filtering:  vtfilter -h bp,f=8270,w=3000
Blanking: vtblank -a12 -d0 -t100
Mixing: vtmult -f 8269.9
Downsample: vtresample -r240 | vtresample -r1
Decoding: ebnaut -dp16K21A -r1 -S30 -k20 -N3 -PU -L500000 -v

Measurements after three repeats:

Todmorden (6194.2 km)
---------------------

  27/28 Eb/N0  +9.2 dB, S/N -22.9 dB/1Hz, phase -140.9 *Decoded*
  28/29 Eb/N0  +5.4 dB, S/N -26.7 dB/1Hz, phase  108.7 *Decoded*
  29/30 Eb/N0 +10.2 dB, S/N -21.9 dB/1Hz, phase  -12.8 *Decoded*

Bielefeld (6917.7 km)
---------------------

  27/28 Eb/N0 -2.6 dB, S/N -34.7 dB/1Hz, phase   71.2;
  28/29 Eb/N0 -2.3 dB, S/N -34.4 dB/1Hz, phase  -45.2;
  29/30 Eb/N0 -3.3 dB, S/N -35.5 dB/1Hz, phase -161.9;

  After phase-corrected stacking: Eb/N0 +2.0 *Decoded*

Warsaw (7681.3 km)
------------------

  27/28 Eb/N0  -7.4 dB, S/N -39.6 dB/1Hz, phase 143.3;
  28/29 Eb/N0 -11.5 dB, S/N -43.7 dB/1Hz, phase  85.6;
  29/30 Eb/N0  -6.8 dB, S/N -40.0 dB/1Hz, phase -46.2;

Cumiana (7173.4 km)
-------------------

  27/28 Eb/N0 +0.6 dB, S/N -31.6 dB/1Hz, phase 164.1 *Decoded*
  28/29 Eb/N0 -2.1 dB, S/N -34.2 dB/1Hz, phase  63.2;
  29/30 Eb/N0 -4.7 dB, S/N -36.9 dB/1Hz, phase -52.6;

Hawley TX (1816.2 km)
---------------------

  27/28 Eb/N0 7.8 dB, S/N -24.3 dB/1Hz, phase  -86.3 *Decoded*
  28/29 Eb/N0 1.3 dB, S/N -30.8 dB/1Hz, phase -163.5 *Decoded*
  29/30 Eb/N0 2.9 dB, S/N -29.2 db/1Hz, phase   55.0 *Decoded*

Forest VA (254.2 km)
--------------------

  27/28 Eb/N0 21.2 dB, S/N -10.8 dB/1Hz, phase  115.9 *Decoded*
  28/29 Eb/N0 20.4 dB, S/N -11.8 dB/1Hz, phase  -14.0 *Decoded*
  29/30 Eb/N0 19.4 dB, S/N -12.7 dB/1Hz, phase -124.1 *Decoded*

Phase shifts to apply before stacking
-------------------------------------

  27/28:    0 deg
  28/29: +118 deg
  29/30: +236 deg

Daily phase change is repeating, perhaps the tx frequency
is actually 8269.9 Hz + 7.78 uHz or 8269.9 - 3.79uHz?
But neither of these offsets improves the individual Eb/N0
at Forest or Todmorden.  Decodes best at zero frequency offset
with constant reference phase.

A suitable filter script to apply the phase shift to I/Q
baseband .vt files:

  #!/bin/bash

  angle=$1   # Degrees of phase advance

  mix=`awk -v "A=$angle" 'BEGIN{
     sinA = sin( A * 3.14159/180)
     cosA = cos( A * 3.14159/180)
     printf( "-c %.3e,%.3e -c %.3e,%.3e\n", cosA, sinA, -sinA, cosA);
  }'`

  vtmix $mix

--
Paul Nicholson
--