Re: LF: Re[2]: VLF: New carrier on 6470.005 Hz

[Markus Vester <markusvester@aol.com>]

Hi Jacek,

in my case, the vast deficit on 6.47 kHz reception is clearly due to QRM from nearby railway lines. On http://df6nm.bplaced.net/VLF/screenshots/vlfwide_170422_1200.jpg , you can see two violet packs of unstable 33 Hz spaced lines, one around 3 kHz and the other above 6 kHz (note that they are stronger than they appear because the antenna ferquency response already rolls off below 8 kHz). I am trying to mitigate the interference by tracking the carriers with SpecLab's automatic multinotch filter, but with limited success.

Looking at the excellent stability even at higher-frequencies, I'm pretty sure that SpecLab's 1pps processing is reasonably precise. In my narrowband instances, the noise blanker is preceeded by a 3.5 kHz wide Bessel bandpass with low ringing, covering both 6 and 8 kHz bands.

On one occasion, the DL0AO receiver in Amberg had produced a marginal 6.47 kHz two-character EbNaut decode. But they are still using various improvised antennas until a proper VLF receive antenna will be ready.

I was actually hoping for better results because Stefan's good reception of my 6.47 kHz carrier proved that daytime propagation at our distance is stronger (in relation to ERP) and more stable than at 8.27 kHz.

Best 73,
Markus (DF6NM)


-----Ursprüngliche Mitteilung-----
Von: Jacek Lipkowski <sq5bpf@lipkowski.org>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mo, 24. Apr 2017 17:10
Betreff: Re: LF: Re[2]: VLF: New carrier on 6470.005 Hz

Paul receives anything (as usual). But the strange thing is that i can
receive the 6470Hz signal with a mediocre setup (suboptimal antenna, qrm
location in the center of Warsaw) at 900km, while Eddie (at 750km
distance) and especially Markus (at 180km) can't receive.

The only other explanation (apart from lower qrm levels) might be the
software used. I use Paul's vlfrx-tools, while Eddie and Markus use
Spectrum Lab. The obvious differences are:

- gps timing (edge in speclab vs "stretched pulse" magic in
vlfrx-tools). not sure what impact this may have

- noise blanker. most speclab setups use the noiseblanker on the whole
spectrum (haven't seen your setup, but this is what most example
configrations i've seen do), while the vlfrx-tools/ebnaut examples use the
noiseblanker only on a 3kHz bandwidth segment centered around the rx
frequency (this could be done with speclab easily too). also the speclab
noiseblanker algorithm might be a bit different

Maybe try vlfrx-tools and see if there is any difference? And if so,
tweak speclab to do the same (especially the filtering/noiseblanker
should be simple)

VY 73

Jacek / SQ5BPF


On Mon, 24 Apr 2017, DK7FC wrote:

> Date: Mon, 24 Apr 2017 15:18:45 +0200
> From: DK7FC <selberdenken@posteo.de>
> Reply-To: rsgb_lf_group@blacksheep.org
> To: rsgb_lf_group@blacksheep.org
> Subject: Re: LF: Re[2]: VLF: New carrier on 6470.005 Hz
>
> Hello Markus, Eddie, Paul,
>
> Thanks for the feedback, for trying and for the results.
> Very strange. Paul has excellent results (as usual) but no decode for Eddie. On
> 8270 Hz, the 'difference' is much less expressed. Does it have to do with local
> QRM only? Maybe...
> Maybe Alex has detected something.
>
> Pauls results are particularly interesting. 1+1 = 1 * 2 = 3 dB. Proves the theory
> :-)
>
> The stacking would help to solve the problems it seems :-) A tool is needed...
>
> 73, Stefan
>
>
>
>
> Am 23.04.2017 23:24, schrieb Markus Vester:
> Hi Stefan,
> I tried to receive your message on both days, and even added the two
> recordings with equal weight, but unfortunately no decode. Guess I need a
> railway strike :-(
> Unfortunately no luck from DL0AO data either.
>
> Best 73,
> Markus
>
>
> -----Ursprüngliche Mitteilung-----
> Von: DK7FC <selberdenken@posteo.de>
> An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
> Verschickt: So, 23. Apr 2017 0:42
> Betreff: Re: LF: Re[2]: VLF: New carrier on 6470.005 Hz
>
> Hi VLF,
>
> another chance, the same msssage two hours earlier, improved timing towards
> the east...
>
>
> f = 6470.100000 Hz
> Start time: 23.Apr.2017   05:00:00 UTC
> Symbol period: 40 s
> Characters: 2
> CRC bits: 32
> Coding 16K21A
> Duration: 11h, 22m, 40s
> Antenna current: 460 mA
>
>
> 73, Stefan
>
>
>