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ULF/VLF: amateur stair case / carrier transmissions

To: [email protected]
Subject: ULF/VLF: amateur stair case / carrier transmissions
From: DK7FC <[email protected]>
Date: Tue, 25 Jun 2019 20:33:05 +0200
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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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