Hello Lubos,
Is the difference of the minimum of the single turn VLF loop higher
than on the multi turn loop? If so, then the single turn loop would be
best for getting an optimal SNR. Interesting!
My DFCW-3 window on my grabber became a DFCW-600 window for while. This
is to compare the old and new SL settings. The upper window uses the
new settings. I am curious about the difference. Hopefully i can get an
improvement in OE3GHB's next transmission :-)
73, Stefan
Am 29.12.2010 08:21, schrieb Lubomir Bobalik:
Hello Stefan!
Many thanks for your effort to improve SL setting. It is as important
as having good antenna. :-)
I wrote your new parameters to my SL setting to try this one. Gerhard,
OE3GHB, was transmiting on 8970 las day, but I didn´t see your signal.
At first, I was surprised, but then I
realised, that my single-loop antenna was beamed to you. It means, that
it was in minimum receiving for Gerhard. I am going to turn it at 217°
and we will see. When I tested single-loop I noticed, there was
difference -20dB between direct beaming and +90° beaming on the beacon
in Germany. It is very much!
Dne 28.12.2010 16:39, Stefan Schäfer napsal(a):
Dear VLF,
In my 9th experiment, my signal was well received at 4X1RF in 2873 km
distance. Chris has recorded the whole procedure and sent me 4.5 GB on
a DVD as a registered letter (many thanks Chris!). I could successfully
extract the 8970 Hz part in a 880 MB file. Then i re-processed this
file several times in SpecLab, adjusting the FFT / Noiseblanker /
Clipper / Filter -settings. This recording is optimal for re-processing
and looking for optimal settings since the SNR is relatively high at
the beginning (up to 12 dB) and becomes lower (due to rising QRN) at
the end. There is a longer section on 8970.00000 Hz and later the
message "CU" that is partly visible and partly lost in the QRN. So the
goal was to make the whole message visible or at least as much as
possible.
The final improvement is rather marginal, probably not much more than 2
dB. The pessimists will say its a pity that the SNR improvement is not
more and the optimists will say its good that we obviously used almost
perfect settings in the last tests ;-)
So, let me tell you about the results:
The left half of the attached picture shows the transmission as
received by using the current distributed USR files/settings (4.5 mHz
FFT, 60 s/pixel, 3 kHz band filter BW, 1 kHz filter slope, Clipper
threshold = 6 dB above avrg., Noise blanker set to 2 ms / 9 dB, 0.05
sec.). The right part shows the best SNR optimisation i achieved. Of
course this is all a subjective decision, there is no strong difference
but i find that the "CU", at least the "C" can be better identified.
Reducing the FFT bandwidth should actually improve the SNR but the
readability decreases! There is not really an improvement between 4.5
mHz and 2.8 mHz, at least in this DFCW-600 transmission.
The SL settings of the best achievement are: 4.5 mHz FFT, 60 s/pixel,
Clipper threshold = 0 dB, Filter BW = 3 kHZ, Filter slope = 1 kHz,
Noiseblanker at 6 dB / 0.0003 sec ramp time, max. pulse width 0.05 sec.
Radio amateurs who are not operating in QRSS/DFCW mode may say there is
no difference between the results ;-)
OK, the different is very good visible. Well done!
On 6470 Hz there was no significant improvement, even in longer FFT
times. But my tests on that part are still not finished.
BTW, without using the SpecLab internal bandfilter, noiseblanker and
Clipper that signal would have been TOTALLY LOST!! There wouldn't even
be the faintest trace of my signal!!
Yes, using all this tools is important, it is "big gun" agains a noise.
I noticed, that Clipper red box indicace "C" continously. The message
says, that "signal is 0,0dB ABOVE clipping (A); avrg=-5,9dB". Is it
correct?
As a conclusion i would say that the current SL settings
are well suitable but a few dB SNR improvement could be achieved. Of
course this depends on the kind of QRN/QRM and the antenna that is
used. The RX stations who can receive my signal at 15 dB SNR or better
will not see a significant difference but the new settings may be
interesting for stations above 1000 km or below. Those who can set up
the SL paramaters may try this. I will provide a new USR file for some
RX stations in high distance before my next VLF experiment.
Any comments/hints are welcome.
When I was active on 137kHz, I had problems with noise and QRM as well.
My best SL configuration used function "reassigned diagram". Using this
function gave very good results. Would be usable on VLF as well, or is
it not suitable for QRSS600? I cann´t try it, becouse I haven´t any
control signal on 8970kHz.
73, Stefan/DK7FC
Have a nice last some days of 2010 year!
Lubos, OK2BVG
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