Message-ID: <59D34A97.4030502@posteo.de>
Date: Tue, 03 Oct 2017 10:30:15 +0200
From: DK7FC <selberdenken@posteo.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <15ec7c794b3-bff-66@webjas-vac136.srv.aolmail.net> <alpine.DEB.2.11.1709281937520.734@mailn.lipkowski.org> <59CD5C56.7000103@posteo.de> <alpine.DEB.2.11.1710022138560.734@mailn.lipkowski.org>
In-Reply-To: <alpine.DEB.2.11.1710022138560.734@mailn.lipkowski.org>
Subject: Re: VLF: SQ5BPF grabber
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

Hi Jacek, VLF,

Thanks for the new grabber. It is the most distant one for me now. There 
are 5 VLF grabbers now, yours is the most distant one for me.
It looks like there is already a faint trace on 6470.005 Hz!! :-)
Your new spectrograms look much better than before i find.
What makes the difference between the view of the vlfrx tools 
spectrograms relative to the SpecLab spectrograms? Mainly the parameter 
settings i assume, or does it have to do with Linux as well?
I'm not really an expert for spectrograms. I just know that in SpecLab a 
Hanning window is used. This makes an overlap between the current FFT 
bin and the neighbour bins, is this right? It smoothes the spectrogram, 
does it?
I know that in SpecLab it is possible to vary the overlap. It is 
normally set to 75%.
When starting a new SpecLab session, e.g. running at 424 uHz, the first 
pixel/spectrum appears after 1/424uHz ~ 39 minutes. Then the next pixel 
appears after 10 minutes, 10 minutes is the scroll rate. So this is 1/4 
of the FFT window time, so the overlap is 75%, because the next window 
has just 25% of new informations, the rest must be from the last pixel. 
This is my understanding, hopefully it is correct :-)
Ah and then there is a function (in SL) called "optimal waterfal 
average". I think this makes only sense when the scroll rate is much 
lower than 1/4 of the FFT window time.
On my grabbers is use for LF
QRSS-3    366 mHz     500ms
QRSS-10    122 mHz    1667 ms
QRSS-60    22 mHz    10 s
and for VLF
DFCW-600    3.8 mHz 1 min
DFCW-6000    424 uHz 10 min
DFCW-60000    47 uHz 100 min (or 60 minutes)
DFCW-600000    4.1 uHz 1000 min
I have a 4.1 uHz spectrogram running at 2970 Hz, but after more than a 
year it is just half filled :-) It still shows my experiments in summer 
2016 :-) BTW that means that windows updates are DISABLED!!!

I think a lower FFT bin width e.g. ~ 47 uHz could be a better choice 
between us.

Just some informations to think about.

Some day i like to produce spectrograms by vlfrx tools as well but i'm 
learning slowly. BTW since a few days, my tree grabber is using vlfrx 
tools (just vtcard and vtvorbis) to do the streaming on MF and VLF. It 
works very well! The quality somehow seems to be a bit higher even.

73, Stefan


Am 02.10.2017 22:02, schrieb Jacek Lipkowski:
> Stefan, thanks for the carrier, this helped me improve my grabber a bit.
>
> i've changed the time range in my grabber to 7 days, so that you can 
> compare with your previous carrier, and also added a "normalised" 
> spectrogram:
>
> https://klubnl.pl/wpr/en/index.php/klubnl-pl-grabbers/grabber-4-8270hz/
>
> in the normalised spectrogram the average of relative powers for each 
> timeperiod are normalised to a constant value. so this is something 
> similar to AGC, taking care of day/night noise variations. i think 
> Paul does something similat, because his spectrogram doesn't show 
> differences in day/night noisefloor.
>
> the S/N isn't great, but this is from a simple e-field antenna in the 
> middle of the city.
>
> i've also added a 6470Hz grabber for your next tests (and will add 
> 5170Hz and normalized graphs in the future):
>
> https://klubnl.pl/wpr/en/index.php/klubnl-pl-grabbers/grabber-sq5bpf-6470hz/ 
>
>
> VY 73
>
> Jacek / SQ5BPF