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Re: LF: SAQ

To: [email protected]
Subject: Re: LF: SAQ
From: Lawrence Galea <[email protected]>
Date: Tue, 6 Nov 2018 12:48:03 +0100
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On 10/26/18, DK7FC <[email protected]> wrote:
> 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.
>>
>> https://www.qsl.net/iz7slz/OPDS/detected.txt
>>
>> Any suggestions and improvements are welcome.
>>
>> 73, Domenico IZ7SLZ
>>
>>
>>
>> On Thu, 25 Oct 2018, 09:30 DK7FC, <[email protected]
>> <mailto:[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:
>>     >
>>
>> 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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