LF: EbNaut Autodecoder 137490 Hz

[Markus Vester <markusvester@aol.com>]

After some playing around, we are running an experimental EbNaut autodecoder at DL0AO and DF6NM under Windows. Receive parameters are currently
 137490.000 Hz, 6 char, 3 s, 8K19A crc 16, start hh:00 and hh:30
and preliminary results can be found here (scroll to bottom):
DL0AO: https://vlf.u01.de/LF/LFgrabber/ebnautresults.txt
DF6NM: https://vlf.u01.de/LF/LFgrabber/ebnautresults.txt

This is nowhere near as perfect as Domenico's Linux solution, and our software contraption is nowhere near a stable state. Anyhow a few test transmissions with a couple of microwatts radiated power lead to useful decodes, and a trace also appeared in the opds spectrogram at DK7FC. It would be nice to find some more signals later...

Best 73,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: Domenico IZ7SLZ <iz7slz.domenico@gmail.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Di, 2. Okt 2018 1:18
Betreff: Re: LF: 2200M EbNaut Beacon

LF EbNauters,

thanks to Markus and Stefan for the comments and to Rob for putting on air a very good signal.

I was also surprised to see the decode achieved by the auto-decoder without any time and frequency offset !

Propagation conditions are becoming better, but noise here is still high.

I tried a deep investigation: no further decode,  but with an offset of -0.0001 Hz and +0.005s (ooops !) i have improved the 2018-09-30_03:00 UT decode:

initial reference phase -62.3 amplitude 2.049e-01
phase   0    0    0    0    0
carrier phase: -6.9 deg
carrier Eb/N0: 0.5 dB
carrier Es/N0: -10.10 dB
carrier S/N: 19.87 dB in 672.0 uHz, -11.86 dB in 1Hz, -45.84 dB in 2.5kHz
elapsed 58
found rank 43 ber 3.4980e-01 Eb/N0 -0.6 M -7.389708042e+00 ph 0 0,0,0,0 [K3RWR_FM18QI_73]

Looking on the October 1st recordings, with these offsets,  i got another decode at 02:30 UT:

initial reference phase -6.6 amplitude 2.356e-01
phase   0    0    0    0    0
carrier phase: -1.2 deg
carrier Eb/N0: 0.4 dB
carrier Es/N0: -10.23 dB
carrier S/N: 19.74 dB in 672.0 uHz, -11.99 dB in 1Hz, -45.97 dB in 2.5kHz
elapsed 58
found rank 84 ber 3.6694e-01 Eb/N0 -1.7 M -7.504411221e+00 ph 0 0,0,0,0 [K3RWR_FM18QI_73]

QRB  is about 7600 km.

Working conditions here, (vintage 😀) as usual:

- miniwhip (a modified ex-Navtex antenna from Furuno ; see attachment)

- receiver JRC NRD-92M with external 10 MHz reference signal steered by  GPS

- a modest PC (Intel P4 CPU 3.50GHz x2) from scrap with Ubuntu 14.04LTS

- software vlfrx-tool from Paul Nicholson.

I have attached also the latest version of  the bash './autoebnaut' i.e. the list of the commands that recall vlfrx-tool programs to start the decoder each 30 minutes.

Other linux programs are running in background:

- vtcard and vttime to manage and calibrate the audio card

- vtwrite to store audio coming from receiver

- gpsd and chrony to manage the nmea and 1pps from neo8 gps (connected at serial COM1) and adjusting the PC clock.

73, Domenico IZ7SLZ