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
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