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Re: ULF: 140 km crossed on the 101 km band, summary

To: [email protected], Renato Romero <[email protected]>
Subject: Re: ULF: 140 km crossed on the 101 km band, summary
From: DK7FC <[email protected]>
Date: Wed, 25 Jan 2017 00:38:06 +0100
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Here are the results of my post processing of my recording from the last weekends experiment. The recording time was just 28 hours, a 9.4 GB file.
The experiment took place in France, JN38OO27QJ The distance to my transmit antenna is 140 km:

The experiment was done on 2970 Hz, with an antenna current of 150...160 mA on my inv-L antenna. The ERP was in the range of 2.8 uW. Up to 17.8 kV was applied to the antenna wire and coil.
On the recording one can find a carrier taking 8 hours, a DFCW-10800 transmission (message 'F') and 4 EbNaut messages.

First, a spectrogram showing the complete recording, without filters and blankers:
The RX antenna is a single turn vertical loop having 40m circumference hanging into trees. It is coupled to the soundcard input by a ferrite transformer with 2 primary turns and 250 secondary secondary turns. On the secondary side, the loop is resonated with low Q, about 40 nF (WIMA FKP-1). Then there is a soundcard powered transistor preamp (ZTX690B) with a RC low pass filter. So the QRN appears pronounced arround 3 kHz. An analog band pass filter with low Q. But it provides more than 10 dB of additional gain on that frequency.
Gives the best overview of the received signals. The carrier is very clear with an SNR peaking > 20 dB in 424 uHz. The DFCW message is partly hard to identify but the human-decoding experts will confirm the character 'F'. Between the DFCW elements (1 hour long each) i transmitted the same character 'F' in EbNaut (8K19A, 1ch, CRC21, 10s), i.e. 3 times. In the morning hours the last DFCW dash was very strong and clear. The final part was an EbNaut message with 7 characters and a long symbol length. Apart from detecting the carrier it was one of the main goals to detect this EbNaut message. 3 of 4 EbNaut messages decoded without a problem. The 7 characer message is so strong that the signal becomes even visible in the 424 uHz spectrogram.
It was a noisy night for this time of the year! A noise background difference of more than 20 dB between day and night.

Screenshots of the detection of the single character 'F':

Screenshot of the detection of the 7 character message 'F/DK7FC'
The signal could have been 10 dB weaker and would still decode easily! More than 50 characters could have been transferred in the same time! So there is MUCH space for further experiments in farer locations :-)

For comparison here's a screenshot of the transmission as received on the tree grabber in 3.5 km distance.

These results are the first international (Germany -> France) detection of an amateur generated signal on ULF (0.3...3 kHz) and a first detection over a distance greater than 1 wavelength.

Last not least some images of the location and equipment (the loop is hard to find, black wire...):

73, Stefan

Am 19.01.2017 21:31, schrieb DK7FC:

This weekend there will be some activity on VLF and ULF!

I'm running my next experiment on 2.97 kHz, my goal is to reach a 140 km distant location in France, JN38OO.

During that time (recording in F/ starting staurday arround 10 UTC) i'm recording the spectrum from 0...12 kHz with a loop pointing to 30/210 deg. It is a very quiet location.

I invited DF6NM and DJ8WX to transmit on 8270 Hz. I guess that Paul, SQ5BPF and RN3AUS as well as DF6NM and DK7FC are watching. Of course everyone is invited to transmit and receive. Transmit stations should announce their time/frequency here, to avoid any collisions. I am only transmitting on 2970 Hz and i expect there will be no one else.

My transmission plan is:

Friday, 20th:
8...17 UTC    carrier on 2970.005 Hz at 150 mA antenna current.

Saturday, 21th:
8...17 UTC    carrier on 2970.005 Hz at 150 mA antenna current.
17 UTC...8 UTC: DFCW-10800 on 2970.005- 2970.000_ Hz (each dash takes 3h, each break takes 1h). Message: 'F'
Between each break (20...21, 0...1, 4...5 UTC): EbNaut, 8K19A, 10s, CRC21, 1ch on 2970.000 Hz

Sunday, 22th:
8 UTC: End of the DFCW transmission
8UTC: EbNaut 8K19A, 32s, CRC16, 7ch on 2970.000 Hz
13:24:16 UTC: QRT.

More details soon...

73, Stefan
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