Новости LF/VLF/ULF/SLF/ELF > SLF (СНЧ — сверхнизкие частоты) диапазон от 30 до 300 Гц
ULF: The next experiment on 970 Hz - Cracked the far field border below
Р6ЛДД:
RSGB_LF:
--- Цитировать ---Hi ULF,
Today i run a carrier transmission on 970.01 Hz. Start time was 08:05 UTC. The carrier run for 3 hours without an interruption. I got 1.9 A antenna current on my ground loop antenna, about 320 W DC input to the PA.
The signal was received on my 3-axis RX on the tree in JN49IK. The distance was, as usual, 55.6 km.
So far the results were disappointing. I expected a strong SNR (at least 10 dB in 424 uHz) from the new E field antenna which seems to perform very well in the complete ULF range. However the analysis of a two hour segment of the carrier showed an SNR of 6 dB, i.e. just noise. However, as i routinely calculated the SNR from the N-S loop i got a surprising SNR of 13.03 dB in 139.5 uHz.
At about 08:40 UTC the reception on the tree was disturbed by its own solar charger, just for a few seconds but that was enough to create a bright vertical line in the 424 uHz spectrogram showing the E field.
Anyway, i just analysed the full 3 hour segment, only from the N-S loop (which actually points rather to 30/210 deg) and got the following result (including processing command line):
vtread -T2018-09-29_08:05,+3h /raw | vtcat -p | vtmix -c0,1,0 | vtfilter -a th=6 -h lp,f=1500,poles=8 | vtblank -a27 -d0.0005 -t100 | vtmult -f970.01 | vtresample -r240 | vtresample -r1 | vtraw -oa | ebnaut -dp8K19A -r1 -c2 -v -f15 -f16 -M'***' -N3 -k20 -S24
carrier phase: -111.2
carrier Eb/N0: 1.9 dB
carrier S/N: 14.25 dB in 93.0 uHz, -26.07 dB in 1Hz, -60.05 dB in 2.5kHz
This is the first far field detection of a 970 Hz signal generated by amateurs on the 309 km band! A true milestone for me. Since more than a year it was my goal to cross that far field border on that band. :-) The efforts were immense.
The result is just preliminary. I want to tweak the parameters for a higher SNR and try to filter out the short QRM from the charger.
So now, why does the E field produce such bad results? At http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/ULFSLFELF.png you can see what it receives in the range of interest. The day/night QRN difference is higher than on the loops, so the loops seemed to be rather deaf. Does it maybe mean a steep reflexion on the ionosphere, so that the E field antenna doesn't see it, but the loops do?
Later i've done a DC measurement and got 1 A at 86.5 V, quite much this time. Maybe a bad contact somewhere. Will check that.
My 120 Ah LiFePo4 accu is fully recharged and i plan to do a new experiment on monday morning, 3 hours before my solar charger starts to work :-) The SNR seems to be promising, i plan to send a 5 character EbNaut message.
More results and a spectrum peak image will follow.
73, Stefan
--- Конец цитаты ---
rw3adb:
В этом эксперименте Стефан применял свою земляную антенну.
rw3adb:
ULF: 5 characer message detection at 970 Hz
Hi ULF friends,
Last morning i transmitted a 5 character EbNaut message on the 309 km band.
At 970.1 Hz i run 1.7 A antenna current into my 900 m spaced earth
electrode antenna. The transmission took about 3 hours.
The DC resistance was quite high this time, about 93 Ohm. Anyway i got
about the same antenna current when running about 300 W.
The QRN/QRM was low and just a few days ago i added a shutdown option to
my solar charger. The Raspi can turn it off by switching a GPIO Pin, so
the off-time can be defined into a script which is executed on the day
when the transmissions happens...
Best results were obtained from the E fied on its own! I got an SNR > 17
dB! See the attachment for details. The message is important these days.
It should be copied by a lot more people.
This is the first far field message detection below 1 kHz
generated/received by amateurs.
QRB, as usual, 57.6 km.
73, Stefan
PS: It was a great sunny autumn day, just like today.
Сергей UB1APE:
Всё ниже, и ниже, и ниже ....
rw3adb:
--- Цитата: Сергей RA1ADF от 22 Октябрь 2018, 08:18:00 ---Всё ниже, и ниже, и ниже ....
--- Конец цитаты ---
да он там уже давно вроде...
ну, ниже 11 гц пока еще никто не вещал)))
так что есть куда стремиться))
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