Re: VLF: EbNaut message attempt DL > VK7

[Markus Vester <markusvester@aol.com>]

WOW! Just reproduced Stefan's one-character message from Edgar's file. That's truly stunning!

73, Markus 


-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Sa, 7. Apr 2018 16:51
Betreff: Re: VLF: EbNaut message attempt DL > VK7

Edgar, VLF,

Thanks for providing the txt files again.
It is amazing! The first day for the 1 char message stack was noisy. Last night, the second day, the noise was 4 dB lower here. The first day produced a carrier S/N of 3.78 dB, last night produced 7.16 dB. The stack of these 2 days produces 8.09 dB!

In the spectrum peak produced by Paul we can see a slight unsymmetry, the left neighbour bin is stronger than the right neighbour bin. This comes from the negative phase change that we can also see at NWC (19.8 kHz) from here. The more or less constant phase change during the transmission is equal to a negative frequency offset, shifting some energy in the left neighbour bin, which becomes already visible in 111 uHz. Thus i played a bit with a frequency offset in the EbNaut decoder and found an ideal SNR of  8.30 dB (i don't tell the offset here for those who like to find it selfe). Applying a frequency offset is valid because there are public reasons to assume a frequency offset can help to improve the SNR

I started a decode attempt and got a decode of the correct message already at phase 0/0/0/0. There were further decodes of the right message but no false decode was shown. Best Eb/N0 is 2.7 dB, best rank is 2058.
When running the decoder without the frequency offset i'm getting even better results, so forget what i said above :-) There are 3 decodes all showing the correct message at convincing rank and Eb/N0.

Unbelivable, we made it after 2 days, and one of them was very noisy! This is all a bit fast to belive i seems. There must have been a reason why SAQ is at 17.2 kHz.

Time to learn the decoding process now. Let me attach the small wav file for everyone here in the list. There are several EbNaut newcomers who like tutorials to reproduce a decode :-)
It is the first amateur radio message on VLF over such a 16805 km distance! And a new distance record for EbNaut message decoding.

Tonite:

f = 17470.1000 Hz
Start time: 07.APR.2018  19:20:00 UTC (daily)
Symbol period: 12 s
Characters: 2
CRC bits: 16
Coding 16K21A
Duration: 02:33:36 [hh:mm]
Antenna current: 1000 mA

73, Stefan

 

Am 05.04.2018 11:15, schrieb DK7FC:

Hi VLF,

Later we have to report about a spectacular success on the path from DK7FC to Edgar J.T..
My daily carrier transmissions on 17470.1 Hz are now completed.

A new experiment will start today: A 1 character EbNaut message:

f = 17470.1000 Hz
Start time: 05.APR.2018  19:20:00 UTC (daily)
Symbol period: 15 s
Characters: 1
CRC bits: 16
Coding 16K21A
Duration: 02:48 [hh:mm]
Antenna current: 1000 mA

73, Stefan