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Re: LF: Heidelberg remote MF receiver

To: [email protected]
Subject: Re: LF: Heidelberg remote MF receiver
From: DK7FC <[email protected]>
Date: Sat, 27 Jun 2015 14:19:06 +0200
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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)

From: DK7FC
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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