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
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