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Re: VLF: Back on 5.17 kHz / 58 km...

from [Markus Vester] [Permanent Link][Original]
To: [email protected]
Subject: Re: VLF: Back on 5.17 kHz / 58 km...
From: Markus Vester <[email protected]>
Date: Sun, 1 Jan 2017 14:04:33 -0500
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20150623; t=1483297474; bh=iWSaq6gIqk/PvhlX66bHGPznkOHM0rC5l6OBz+8GYTM=; h=From:To:Subject:Message-Id:Date:MIME-Version:Content-Type; b=Hl3mJ4yC8gYYoyW4J+VrxYGNt0v5MUhevkeeEHwI8UGuWVoXBuRk5CgB+a54AYYAn sVit32OwpH+7+zFqmIUMt0qEvzEkUJ3VWqhZxbfpMHkXUZZPaYYCKyyIuotffnaGv7 Oi7lOXAdxhxUTOoTXi7C5VNmYpStxomEU5IdpDLg=
In-reply-to: <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Unfortunately Stefan's "58" message did not decode correctly here, best guess was "DJ" at rank 4675. During the PSK transmission, a suspicious carrier peak was still visible in the red rawsyms spectrum. Choosing 80 s instead of 60 s produced the well-known "**" "Asterix"-decode.

Thus I believe that the 5170 Hz line in my 63 uHz spectrogram was probably due to leakage of the 1pps reference signal into the left audio channel. Considering the unshielded and untidy antenna wiring on my workbench 
 http://df6nm.bplaced.net/VLF/pictures/VLF_loop_preamps_and_combiner_annotated.jpg ,
 http://df6nm.bplaced.net/VLF/pictures/VLF_antenna_connections_annotated.jpg ,
this is not completely unexpected (the green GPS cliplead may have come too close to the E-field isolation transformer). However it's not easy to investigate such low level interference which needs hours of FFT integration to stand out.

Anyway Stefan's 0.25 mHz frequency step will hopefully prove things one way or another.

Best 73,
Markus (DF6NM)

PS I also tried the 16k25a transmission today. But starting the EbNaut decoder immediately sent the 8 GB machine into disk-swapping nirwana, requiring a hard reset.


-----Ursprüngliche Mitteilung-----
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>; Renato Romero <[email protected]>
Verschickt: So, 1 Jan 2017 4:19 pm
Betreff: Re: VLF: Back on 5.17 kHz / 58 km...

Hello Paul, VLF,

My congrats, the message is correct! :-) The first EbNaut on 5170 Hz!!! :-)
I did not stop transmitting since friday afternoon (unfortunately this makes my LF grabber unusable). So maybe you got some first informations about propagation on 58km?
It seems to be a promising band, at least in that range of distances.

There is even a trace in Italy!!! Renato can see a trace on 5170 Hz, see http://www.vlf.it/cumiana/livedata.html
I will make QSY to 5169.99975 Hz at 16 UTC, hopefully the step becomes visible on his grabber :-)
Maybe he even received the EbNaut message? Could you check that?

The QRN levels become lower there, relative to 8270 Hz or 6470 Hz. That's not only the frequency response of my VLF RX.

BTW i sent another EbNaut message today:

f = 5170.000000 Hz
Start time: 01.Jan.2017   09:00:00 UTC
Symbol length: 20 s
Characters: 3
CRC 16
Coding 16K25A
Duration: 5h, 09m, 20s
Antenna current: ~ 200 mA

30 second symbols would have been a better choice but i had to make a quick decision :-)

73, Stefan


Am 31.12.2016 17:41, schrieb Paul Nicholson:

Stefan wrote:

> f = 5170.000000 Hz
> Start time: 31.12.2016   09:00:00 UTC
> Symbol length: 60 s
> Characters: 2
> CRC 16
> Coding 8K19A

I wrote:

> I expect an easy decode at about Eb/N0 = 4.5dB

Copied '58' with Eb/N0 = 4.5 dB, constant reference phase.

S/N: 15.06 dB in 45.3 uHz,  -62.4 dB in 2.5kHz.

--
Paul Nicholson
--

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