Hi Markus,
Thanks. Indeed, i actually saw you in the morning with "O" copy in the
garden, while it was "T" copy in the city. Switching from the T antenna
to the loop didn't rise your SNR (to that time! Now there is heavy QRN
from a thunderstorm near Frankfurt) but a few local QRM traces
disappered, so the spectrogram looks nicer.
It was interesting to see the drift in the morning, several Hz! I've
switched the QRSS-30 SL instance to stereo mode now and locked it to
FTA (20.9 kHz) which is barely detectable on VLF with the small ferrite
antenna. Maybe i will soon use the right channel for the VLF loop. That
should give a much better signal level. And BTW it would be interesting
to see the SNR difference between city and garden on VLF!!! :-) I will
trun the loop to EW. Or maybe Uwe/DJ8WX is still operating there?
73, Stefan
PS: I reduced the quality factor of the stream from q=1.0 to q=0.8
which reduced the data rate from 460...520 kbps to 250 kbps (daytime,
now QRN) ... 350 kbps (QRN, like now!), so there is some room left...
Am 27.06.2015 00:39, schrieb Markus Vester:
Hi Stefan,
it looks like signals are
consistently better on your remote receiver, perhaps around 6 dB or
something in that ballpark. So it seems that all your work is finally
paying off! I'm looking forward to see a daytime comparison tomorrow.
My guess is that the main
contributor to frequency variation would be the 461 kHz LO crystal
rather than the soundcard samplerate. Anyway exchanging the 12 MHz
crystal may possibly have no effect at all, because the samplerate of
USB soundcards is usually derived from the bus master clock (ie the
RasPi) and not from the internal crystal on the dongle.
Best 73,
Markus (DF6NM)
Sent: Friday, June 26, 2015 11:22 PM
Subject: Re: LF: 476.181 kHz from indoor loop
Hi Markus,
Really? Wonderful! :-) And the stream is still running. I'll watch it
some days now to see if all Raspi problems are gone, then the next
part-project is the RX.
Meanwhilethe sky wave is present and i can see you quite strong in
DFCW-30 with your 3 mW ERP from the loop. I missed watching you on the
remote grabber in daytime. What was the SNR ralative to the city
location? Same or better? I switched back to the T antenna in the
afternoon. It would be interesting so see you on my loop. On 21:19 i
switched to the loop!
Ah and now you can see the drift of my RX which is quite visible, but
still uncritical for QRSS-30 or WSPR.
I thought about changing the 12 MHz xtal of the soundcard. It is the
cheap SMD xtal which has 100 ppm/K but there are other versions with 30
ppm/K. Maybe an idea, they are no expensive and still compact...
73, Stefan
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