ULF: New earth antenna experiments

[DK7FC <selberdenken@posteo.de>]

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

900m_earth_antenna_frequency_response.png
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8270_tuned.PNG
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8270_49.2deg.PNG
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