VLF: TA decodes from W4DEX and VO1NA in Amberg

[Markus Vester <markusvester@aol.com>]

During the last week, transmissions from Dex W4DEX and Joe VO1NA have been successfully decoded from the DL0AO cardioid antenna.

The three-character message from W4DEX was copied after stacking the six available nights, using transmit phase corrections published by Paul. A unique decode at rank 3867, Eb/N0 -2.6 dB was already achieved using equal magnitude (phase only) weights. It was improved further to rank 829, Eb/N0 -1.9 dB by using the same phases with approximate inverse-noise-power weights, as shown in the table below. No local correlations were used to derive the weights. The strong CRC apparently helped to prevent false decodes even at marginal SNR. Comparing the result to the previous decode from Jay W1VD has confirmed that our received message is indeed correct.

W4DEX - DL0AO 8269.9 Hz
2017-12-27 to 2018-01-03

night    weight
           dB  deg
27/28   -6    0
28/29 -10  118
29/30   -8  236
30/31   -4  260
31/01 -14  103
02/03 -10  245

After having received VO1NA's previous "S", the next one-character message was again decoded successfully from two single nights. Stacking seven nights with equal gain and phase then produced a very robust rank 0 decode. The result has been confirmed by Joe.

VO1NA - DL0AO 8270.0075 Hz
2017-12-28 to 2018-01-04

night EbN0 rank decode

           dB
28/29  0.5    5   correct
29/30  0.1  28   correct
30/31 -0.3  48   false
31/01 -0.3  49   false
01/02 -0.1  10   false
02/03 -0.5  27   false
03/04 -0.4  18   false
sum    2.4    0   correct

Guess that wasn't a bad start into 2018... many thanks again to all contributors!

Best 73,
Markus (DF6NM)



-----Ursprüngliche Mitteilung-----
Von: Markus Vester <markusvester@aol.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Do, 28. Dez 2017 17:50
Betreff: Re: LF: Re[2]: LF: VLF NA Ebnaut

Big CONGRATULATIONS to Alex and Joe!

I'm glad to announce that the one-character EbNaut transmission from VO1NA has also been decoded from the cardioid antenna at DL0AO (near Amberg, JN59VK). The correct decode "S" first prevailed in a single-night recording from Dec 23/24, and finally became absolutely unambiguous after stacking four out of seven nights with equal gain and phase.

Correlations for single nights:
 Eb/N0 phase night
  dB   deg   Dec 2017

 -5.5 -54.3  21/22
 -4.8  -8.5   22/23
 -0.5  -6.5   23/24  (decoded "S")
-20.6 150.3  24/25 (only noise)
-10.7  32.1   25/26 (only noise)
 -2.5 -26.5   26/27
 -4.4  10.8   27/28

Two nights stacked:
 +0.6  -7.3  22/23 + 23/24
 -0.8   -9.5  26/27 + 27/28

Four nights stacked:
 +2.8  -8.4  22/23 + 23/24 + 26/27 + 27/28

Thanks to Joe for sending consistent repeats, to Bernd and Tom for setting up the VLF receivers at DL0AO, and of course to Paul and Wolf for making all this possible in the first place.

Best 73,
Markus
...

w4dex_dl0ao_27 28 29 30 31 2_hidden.png
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VO1NA-DL0AO_28 29 30 31 1 2 3_hidden.png
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