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: [email protected]
[mailto:[email protected]] On Behalf Of DK7FC
Sent: Monday, August 6, 2018 9:02 AM
To: [email protected]
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
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