Hi Domenico,
Thanks for the feedback.
Is the auto-notch filter necessary at 17.2 kHz? Hopefully it doesn't
trigger on the SAQ signal and removes it ;-)
Maybe not a suggestion, just my point of view (you asked about it):
The noise blanker may improve the S/N but listening to a CW signal
doesn't sound so good when a noise blanker is used. Also i would choose
a smooth filter, low pass + high pass, maybe combined with the brick
wall filter. There is/was that Russian transmitter arround 18.2 kHz,
very strong here. It will lower the performance of the noise blanker.
Here i used vtread | vtcat -p | vtmix | vtmult -f16500 | vtmix -c1,j |
vtfilter -h hp,f=850,poles=10 -h lp,f=550,poles=10 -g1000 | vtresample
-r4000 | vtraw -ow > audio.wav
..., i.e. i convert the SAQ signal to 700 Hz, apply a rough band pass
filter, resample to 4 kS/s and then i read the wav file in SpecLab and
apply a rough noise blanker (high threshold, just for the few very
strong sferics), then a better CW filter and then a slow AGC.
Are you regularly archiving the VLF stream from your soundcard to a
database (using vtwrite) ?
73, Stefan
Am 26.10.2018 00:20, schrieb Domenico IZ7SLZ:
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
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:
> https://drive.google.com/file/d/1QzJYH8GajL2PzCngnkteNT3p5vBN-tAY/view?usp=sharing
> In perfect 'vintage' marine radio officer style, i have prepared
the
> text sent by SAQ :
> https://drive.google.com/file/d/1R36BPmf5lyiAlOzDj-bj1dZuNkKleQt3/view?usp=sharing
>
> a nice text about the Peace. Thanks to the SAQ staff for their
activities.
>
> 73, Domenico IZ7SLZ
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