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Date: Mon, 6 Aug 2018 13:20:38 -0400
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Subject: LF: RE: New earth antenna experiments
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Stefan,

Excellent V, I and time-domain data, a wonderful sight.

The inductance extrapolations generally fit an "AWG 18 (on surface) plus earth-loop" model*, which is very nice to see, and the time-domain plots are fascinating. From the time-domain plots, it looks like the loop could perhaps be roughly modeled as two Ls and two Cs. I wonder (pure speculation) if the two-L/two-C appearance in the resonated waveform has anything to do with the difference between the following two sections of the loop:
(a) the thin (AWG 18, hence much more inductance per meter than the through-earth path) horizontal wire on the surface air/earth interface (i.e. three unique properties in this near-surface section of the loop), and:
(b) the much-wider [30-meter 1-sigma current cross-section(?), therefore much less inductance per meter than the through-copper path) near-semicircular current path through the earth (i.e. two unique properties in this all-subsurface section of the loop).  

Your data from DC to 8270 Hz, with and without resonators, seems to paint a promising picture for lower frequencies (fairly well-behaved impedances DC through 8270 Hz), and shows intriguing nuances that might fit a meaningful model (I will try a SPICE model this afternoon). High compliments to the experimental design that provides this high quality data!

73,

Jim AA5BW

* (home-made ROM model)   

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of DK7FC
Sent: Monday, August 6, 2018 9:02 AM
To: rsgb_lf_group@blacksheep.org
Subject: ULF: New earth antenna experiments

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