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Re: LF: EbNaut Autodecoder 137490 Hz

To: rsgb_lf[email protected]
Subject: Re: LF: EbNaut Autodecoder 137490 Hz
From: Markus Vester <[email protected]>
Date: Sat, 6 Oct 2018 07:17:03 +0000 (UTC)
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In-reply-to: <[email protected]>
References: <[email protected]> <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Last night, Domenico IZ7SLZ and myself had an unscheduled EbNaut two-way contact ;-) Well not quite a QSO, as we didn't exchange reports etc. I had sent a couple of 6-character messages into the blue before going to bed, and was pleasantly surprised this morning to find Dom's replies on all three automatic decoders.

Attached 477 uHz spectrogram from DL0AO shows both EbNaut signals, along with a few other WSPR and Opera transmissions, and 6.25 Hz spaced Loran lines from Slonim. Note that the receive level of nearby stations (DK1IS and DF6NM) is being reduced by SpecLab's frequency-selective limiter to avoid overloading and noiseblanker artifacts.

Thank you very much Dom! Now we're hoping for more and distant signals, like from Spain or U.S. ;-)

73, Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: Markus Vester <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Mi, 3. Okt 2018 14:46
Betreff: LF: EbNaut Autodecoder 137490 Hz

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):

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 <[email protected]>
An: rsgb_lf_group <[email protected]>
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


Attachment: autodecoders_181005_iz7slz_df6nm.txt
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Attachment: dl0ao_lf4_181006_0620_annotated.jpg
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