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Re: ULF/VLF: amateur stair case / carrier transmissions

To: [email protected]
Subject: Re: ULF/VLF: amateur stair case / carrier transmissions
From: DK7FC <[email protected]>
Date: Wed, 26 Jun 2019 08:03:39 +0200
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Hi Markus,

Yes and it was a relatively quiet day. On my tree i got 27...30 dB SNR in 11 mHz on the higher frequencies, enough to calibrate the colours precisely.
The coulours of the DL0AO grabber seem to be aligned very well! My 'dot' in the 424 uHz spectrogram shows the correct direction. Did you apply a correction table for the colours there or is the phase response of the 3 antennas actually flat?

With the new setup at DL0AO i bet we can soon detect something below 1970 Hz, which is so far the lowest frequency that was detected in > 1 lambda.

73, Stefan

Am 25.06.2019 21:31, schrieb Markus Vester:
Hi Stefan,

good work! You chose the best time of the day, producing nice bright dots in the DL0AO 424 uHz spectrograms, estimated SNR up to 25 dB SNR on 8270 and close to 30 dB on 5170 Hz. I'm curious what you will derive from the recordings.

Best 73,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Di, 25. Jun. 2019 20:35
Betreff: ULF/VLF: amateur stair case / carrier transmissions

Hi all,

Today, some 20 minute long carrier transmissions were drone from JN39WI
again. The main intention was to calibrate my local RDF spectrogram
(still to be done) in the range below 16.4 kHz (JXN) and above 82 Hz
(ZEVS). So that was a amateur radio ULF/VLF staircase somehow, despite
the weak signal strength relative to commercial transmitters.

It was a hot day! Far > 30 C here. I started early in the morning and
enjoyed the fresh air in the forest.

The DC resistance of the 1130m ground loop increased to 73.2 Ohm
(measured at 1 A) due to the dry soil. It confirms the dependency shown
in the last year! In 2018 i saw the resistance rising up to 94 Ohm in
late October, then it dropped to 57 Ohm (-40 %) in just 2 months.

It was interesting to see that the antenna current is much higher at
lower frequencies (always at resonance | the PA output voltage is nearly
constant). This effect was very clearly expressed.

IF of interest for other stations (having a data storage):

Frequency/Hz    Start time/UTC                        Antenna current/A
970.005            2019-06-25_08:36:20,+20m    2.26
2970.005          2019-06-25_08:13:30,+20m    2.19
5170.005          2019-06-25_07:51:00,+20m    2.09
8270.005          2019-06-25_07:23:00,+25m    1.85
end of the official part.

BTW, since a few days, the VLF RX site at DL0AO has a 3 axis VLF
receiver recording data from a Octo-soundcard and a Raspberry pi 3,
saving data to a 4 TB HDD so there is one more station that won't miss
anything from now on (for example unannounced transmissions by SAQ).

Some spectrograms may be shown later.

Evetually there was a problem with the sample rate correction due to the
upheating car, which caused a high deviation of the tracked sample rate.
The max allowed range of 10 ppm was left in the end of the experiment
but this was noticed a bit late, maybe.

73, Stefan

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