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Re: VLF/ULF: Improved grabber from the tree...

To: [email protected]
Subject: Re: VLF/ULF: Improved grabber from the tree...
From: [email protected]
Date: Tue, 3 Jul 2018 09:44:18 -0230 (NDT)
In-reply-to: <[email protected]>
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Hi Stefan,

Well done on your setup; it's inspiring. On the day of the SAQ transmission, the 10 uW sigs on 8270.0075 Hz could be heard at 3.3 km
which is a new distance record for me on VLF CW. The TX is back to
an unmodulated carrier again.

73 and GL

On Sun, 1 Jul 2018, DK7FC wrote:


In the last weeks i finally installed the octo-soundcard for the raspberry pi on the tree. Now i can listen on 6 channels simultaneously. So now i am able to track the signals of both of my orthogonal VLF loops mounted in 18m above the ground.
The raspi is running vlfrx-tools. A GPS module provides accurate timing for
the system, so it does not depend of an available internet connection
providing the ntp service. The sample rate is corrected on the tree and a
stream is generated which includes timestamps.
2 channels are used for the MF loops. Another 2 channels is used for the VLF
loops now and one channel is for the 1PPS+NMEA. So there is 1 channel left!
The idea is to build an E-field RX for VLF so i can generate a 360° RDF
spectrogram. But it would also be nice to have something for LF... There
should be even more channels on the input :-)
Anyway, now i can already generate RDF spectrograms. They are hidden on my
grabber page,
If you click on one of the spectrograms, it will switch to the RDF mode. Not
all of the images are available in RDF mode. The other channel show the
signals of the E-W loop. I should add a 3rd image showing the N-S loop but i
have to see where i can find another computer running a few more SL instances
So far i'm still fighting with stream interruptions. Streaming 5 channels
(two of them are vorbis streams and three of them are flac streams (lossless
compression!)) means a significant data rate over the 2.4 GHz WLAN link.
Thus, another task for the coming days is to move to 5 GHz where higher data
rates should be no problem.
I'm saving 100 GB of the data of the VLF loop so i can post-process the
signals of about the last 2 weeks (the stream is resampled to 24 kS/s). That
means i can configure a 'totary loop', software based.
So now, if VO1NA and IW4DXW transmits a message in the same time, i can watch
for both of their signals and even 'turn' the loop for the best S/N for each
station :-)
Joe's carrier has been very weak here and the common dark time is very low
and but the QRN is very high. So there are doubts that i will detect the
carrier but it may be worth a try :-)
If someone else wants to try to transmit down there, don't hestitate :-)

73, Stefan
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