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Re: ULF: The next experiment on 970 Hz - Cracked the far field border be

To: [email protected], Renato Romero <[email protected]>
Subject: Re: ULF: The next experiment on 970 Hz - Cracked the far field border below 1 kHz
From: DK7FC <[email protected]>
Date: Wed, 03 Oct 2018 21:23:40 +0200
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Hi ULF friends,

Here are the final results from the carrier analysis of the recent ground loop antenna transmission on 970.01 Hz.

I had to learn how to mix the 3 antennas properly to achieve the best SNR. It helped a lot to turn the phase of the E field relative to the loops. The final SNR of the 3 hour exceeded 16 dB, which is quite a good result, remembering and scaling the SNR i got on 1970 Hz or 2470 Hz when using the same TX antenna and similar power.
Now the processing chain and result is:
vtread -T2018-09-29_08:05,+3h /raw | vtcat -p | vtmix -c-0.1,1,-0.7/60 | vtfilter -a th=7 -h lp,f=1500,poles=8 -h hp,f=400,poles=8 | vtblank -a29 -d0.0005 -t80 | vtmult -f970.01 | vtresample -r240 | vtresample -r1 | vtraw -oa | ebnaut -dp8K19A -r1 -c2 -v -f15 -f16 -M'***' -N3 -k20 -S24
carrier phase: 73.6
carrier Eb/N0: 3.9 dB
carrier S/N: 16.24 dB in 93.0 uHz, -24.08 dB in 1Hz, -58.06 dB in 2.5kHz

It would have been possible to transfer a 7 character EbNaut message with that signal.
Attached you can find a spectrum peak plotted from the data. Also there is a spectrogram showing the trace in 212 uHz FFT bin width.

73, Stefan

PS: I noticed that the actual distance between TX and RX is 57.6 km. So i could cross the far field border down to 830 Hz on that path ;-)

Am 29.09.2018 23:00, schrieb DK7FC:

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 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

Attachment: 970Hz_Träger212uHz.png
Description: PNG image

Attachment: 970Hz_Träger212uHz_2.png
Description: PNG image

Attachment: carrier970Hz_spectrum_peak.png
Description: PNG image

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