SLF,
For the completion of this thread, here is the reprocessed spectrogram
of a DFCW-5400 message at 80 Hz (attachment).
It is just a small distance but anyway challenging, on the TX side as
well as on the RX side.
Usually i want to detect a carrier, then an EbNaut message and finally
a DFCW message when visiting one of these really low bands.
Next step is ELF at 23 Hz but this is even more challenging. Thus there
is some delay...
73, Stefan
Am 27.11.2018 09:25, schrieb DK7FC:
Hi SLF,
Yesterday, a 45 character EbNaut was transmitted at 80.005 Hz. It was
received on my tree in 3.5 km distance. After the improvement of the RX
antenna it looks like i gained about 2.5 dB SNR. It was an easy decode,
the message could have been transmitted 4 times faster.
Capture attached :-)
73, Stefan
PS: With that SNR, a 5 character message could be transferred out to 7
km distance in less than 1 day.
Am 23.11.2018 10:21, schrieb DK7FC:
Dear SLF friends,
A new step forward towards DC: Since yesterday 22:30 UTC i'm TXing a
carrier at 80.005 Hz. That's the 3750 km band, where
the far field begins at a distance of 598 km.
The antenna voltage is just 5 kV and i'm getting 1.2 mA antenna
current, giving an ERP of 20 fW (2E-14 W).
The voltage is even higher than in my recent experiment on 270 Hz,
anyway the S/N is lower, indicating that my RX lacks of sensitivity.
Indeed this experiment helps to estimate the lack of sensitivity. Looks
like i'm missing about 10 dB on that frequency. Anyway the signal is
making the path of 3.5 km to my tree grabber, as usual shown at http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html.
Not
a
big distance but still well beyond most garden fences!
The signal leaves a barely visible trace in the ZEVS window which is
running at 3.8 mHz FFT bin witdh. Unfortunately ZEVS is off the air
since a week or so. actually i wanted to transmit side by side with
ZEVS, of course a bit deeper even.
>From a quiet period at night, i calculated the SNR of a 1 hour carrier
period using vlfrx-tools: carrier S/N: 16.83 dB in 277.8 uHz,
-18.73 dB in 1Hz
For the crazy homebrewers i'd like to share that website where i
ordered the HV-transformer, http://www.hosin.de/Specials/HV-Trafo/hv-trafo.html
A nightmare for all
safety-fetishists! For the completeness it must be mentioned together
with that page: http://kurts-werkstatt.de/hv-trafo.htm
73, Stefan
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