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To: [email protected]
Subject: Re: LF: SAQ
From: Domenico IZ7SLZ <[email protected]>
Date: Fri, 26 Oct 2018 00:20:50 +0200
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Hi Stefan,

Thanks for informations on your temporary setup for SAQ.

For this last SAQ reception, I have used vlfrx-tools to acquire (vtcard) and record (vtwrite) the VLF signal coming from E-probe antenna.Then filters, NB and vtvorbis have been used for stream the 'RF' to the other pc where Spectrum Lab is running.

vtfilter -v -h bp,f=17200,w=3000 @input:1  |          # Pre-filter before blanking
vtfilter -v -a th=5 |                                                # hum filter
vtblank -v -a15 -d0 -t300 |                                    # sferic blanker settings
vtresample -v -r 48000 |                                       # Reduce to 48000 sample pairs/sec
vtvorbis -v -ep -t -q1 -kn 1236                               #port 1236

So, in a similar way as your setup Stefan,  Spectrum Lab here uses this stream, a  bp filter with a frequency shift (to obtain a central frequency of  700 Hz) and an AGC (slow) before the D/A converter (see attached screenshot).

Maybe there is a better way to stream the raw audio to a Windows PC but this i'm using is working ok.
I also use this method to stream LF audio (filtered and timestamped by vlfrx-tools) into another pc  where SL and OPDS are running.

Any suggestions and improvements are welcome.

73, Domenico IZ7SLZ

On Thu, 25 Oct 2018, 09:30 DK7FC, <[email protected]> wrote:
Hi Domenico,

Which filter settings did you choose to obtain the CW filter?

I also used vlfrx-tools to extract the SAQ message. The SNR was much
stronger on the N-S loop than from the E field. Mixing E and H
(including a small portion of the E-W loop) resulted in an SNR increase
of > 6 dB.
But in the end i used SpecLab to build the CW filter, a rough noise
blanker for the very loud sferics (12 dB threshold) and finally a slow
AGC which made it even more comfortable to listen to...

73, Stefan

Am 24.10.2018 23:35, schrieb Domenico IZ7SLZ:
> Good reception of SAQ here in JN80nu thanks to very low QRN and to
> Paul's vlfrx-tools used for acquiring, filtering and stream the audio
> to Windows PC.  Then i have used Spectrum Lab to convert to analog and
> send the audio to the speaker. Path is about 2300 km.
> This is the audio recordered:
> In perfect 'vintage' marine radio officer style, i have prepared the
> text sent by SAQ :
> a nice text about the Peace. Thanks to the SAQ staff for their activities.
> 73, Domenico IZ7SLZ

Attachment: saq-setup.JPG
Description: JPEG image

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