SLF (270 Hz, 80 Hz and 60 Hz) experiments and observations have been
fascinating. It’s been enjoyable to guess what your next result would
be; and encouraging to see that things at 270 Hz and 80 Hz seem fairly
well behaved so far. It was also interesting to notice on your grabber
that the 60Hz fading might not be diurnal.
question regarding your ZEVS and SLF spectrograms:
your ZEVS spectrogram (79.8 Hz – 83.2 Hz span) show lower SNR for your
80 Hz signal than your SLF spectrogram (79.95 Hz – 80.05 Hz span)
because one comes from an H-field sensor in the forest and the other
comes from an E-field sensor in the forest? The integration time
difference (3.8mHz vs 424 uHz?) would seem to account for 9.5 dB lower
SNR at 3.8 mHz, but the SNR in the ZEVS spectrogram (3.8 mHz) seems
lower by more than 10 dB, so I wondered if the two spectrograms came
from different antennas.
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 :-)
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