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ULF: New earth antenna experiments

To: [email protected]
Subject: ULF: New earth antenna experiments
From: DK7FC <[email protected]>
Date: Mon, 06 Aug 2018 15:01:38 +0200
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Hi ULF,

Despite the ultra high temperatures (> 35 °C here) i worked 6 hours to separate the wires from the loudspeaker cable and rolled it out between the two guide rails. About 850 m of wire was needed to connect them. I define the antenna length as from the center of the guide rails, so 900m is quite accurate. After that work i was quite down but i couldn't wait another day for the first results of the measurements. So i characterised the transmit frequency response (V/I ratio and reactive component) from DC to 8.27 kHz on frequencies of interest. I used a good oscilloscope to measure the voltage / current waveforms and the phase between them. Then i added a series capacity to resonate the earth loop. You can find details in the attached table. The inductivity is calculated from the frequency and the tuning capacity.
To my satisfaction the DC resistance showed exactly as expected: 79.4
Ohm. So i reduced the losses by more than 50 %, relative to the 0.4 mm
diameter Cu wire i used the weekend before :-)
Attached i also show a plot from the scope showing the un-tuned (no C in
series) loop at 8.27 kHz. The yellow trace is the voltage at 20 V/div
(100:1 divider).. The antenna current is blue and at 250 mA/div
(measured across a 0.2 Ohm shunt resistor). Also attached, the tuned
antenna at 8.27 kHz showing a good sine curve for the current showing
750 mA (rms).
The next day i transmitted into the ULF band. Results will come soon in
a separate email.
73, Stefan

PS: Oh and here is an image from the portable shack: http://www.iup.uni-heidelberg.de/schaefer_vlf/ULF/ULF_shack.jpg

Attachment: 900m_earth_antenna_frequency_response.png
Description: PNG image

Attachment: 8270_tuned.PNG
Description: PNG image

Attachment: 8270_49.2deg.PNG
Description: PNG image

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