VLF,
After nearly 8 days the carrier is still on the air without an
interruption, despite occasional thunderstorms :-)
It looks like the SNR is suffering by summer QRN, as expected.
The stable carrier was good for doing local tests with my
Raspi+Octo-soundcard. The system is now completely configured including
system time setting via the GPS module. I recorded a few days from the
carrier, converted the data files into wav, reprocessed them in
SpecLab: The carrier is stable and on the expected frequency, so the
sample rate correction via vlfrx tools seems to work.
Forthermore i corrected some bugs in the circuit of my portable RX loop
preamp for VLF (must have been late in the night when i built it up a
few months ago). Now the noise is much lower. It looks promising! So it
is time for a portable VLF experiment in the far field, just to check
the system more seriously.
The crew of DL0AO has built up and optimised their VLF system to
receive the weak 3675.005 Hz carrier in abt 220 km distance. Looks like
there is something on their cardioidal spectrogram pointing to West,
http://df6nm.bplaced.net/dl0ao/VLFgrabber/vlfgrabber_dl0ao_test.htm
Something like 10 dB SNR in 31 uHz. That's not so bad!
I will run it for some more time until the trace is a bit longer. Then
in some days i like to start transmitting an EbNaut message on that
frequency which can be stacked until a decode appears. Markus has
developed a tool for windows to do the stacking, maybe it works in that
experiment... It will also be a test to see if i can decode the message
from my own recording using vlfrx tools, an important step to pass...
So far so good. What are YOUR projects you are currently working on,
LF/MF/VLF related?
73, Stefan
Am 28.07.2017 16:56, schrieb DK7FC:
Hi VLF,
I'm back from LF for a while and built up my large VLF coil which was
used on 2970 Hz in the beginning of the year. Actually it is under
maintenance, one of the six stacks has to be replaced. It is already
dismantled but the new wire is not yet wound on the 250 mm diameter PVC
tube again.
So now the resonance is higher! I didn't know where it is and just
connected the coil and scanned the frequency downwards. Near 3685 Hz i
found a maximum of the antenna. Since the Q is not extremely high, i
decided to tune to 3675 Hz and added the usual 5 mHz offset, to stay
away from multiples of 1 Hz.
So, now since 14:40 UTC a carrier is running on 3675.005 Hz.
The
antenna current is 170 mA. I estimate the ERP is just 3
uW!
I guess this is a first amateur radio transmission on the 82 km
band and that class of ERP (?).
Hopefully the coil will hold the 15.5 kV with just 5 stacks of
windings. It's inductance is 3.9 H in the moment!
I intend to run the carrier for at least a few days, depending on the
feedback.
Good luck for the VLF experts!
73, Stefan
PS: A 424 uHz RDF spectrogram is running at
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
(First pixel appears in 30 minutes)
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