Hi VLF,
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,
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
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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