Hell Roger, Dreamers,
yesterday I tried to reproduce Rogers experiments with VLF transmissions over
the local gas and water mains.
I connected one wire to the equipotential busbar of my house. The other wire is
connected to a 60cm copper rod in about 15m distance in the garden - very
similar to Rogers setup. I measured about 180 ohm DC. I tried different
frequencies below 9kHz with an audio transformer.
The "walk around" reception was very disappointing, just a few meters. No way
to receive something walking down the street even 100 meters.
Because of the relatively good ground conductivity here it is not surprising
that the setup does not work as a ground loop. But I had expectected some
induction along the mains like at Rogers QTH.
As I do not assume that gas and water pipes of my house are all isolated from
the pipes in the street there is just one explanation: The good ground
conductivity.
After that I tried to reproduce the test with the 100m earth base I did some
weeks ago. I could hear my signal (Or was it a false signal.) at about 500m.
This time also nearly nothing - like at my very first test with an 30m earth
base in my garden.
I had assumed that after some hot sommer days without rain the ground
conductivity would be lower and the results with my earth antenna would be
better.
It seems my QTH ist not suitable for earth antenna tests at all.
To verify that I next took my T-antenna (10h20t) and the TV transformer. The
result: Still audible signal in 100m distance. So I assume that ground
conductivity has not changed very much since my previous tests.
Assuming that the T-antenna would work worse after some hot days without rain I
was surprised by that.
To verify that I will leave the busbar supported earth base installed so I can
measure any time, especially after the next heavy rain. I know that measuring
Ohm DC is not measuring ground counduktivity or even impedance. But it will
give a glimpse of how of the influence of weather and humidity at my QTH.
The last test was more for fun. I connected my 2x27m Inverted Vee and the both
(13m) Wireman cores to the TV transformer instead of the T-antenna. Dispite of
more than the double of wire this works worse. So I found confirmed what I hat
learned about T-antennas and top loadings: not as Inverted V.
This tests have shown the limits of what is possible at my home QTH on VLF.
The next step will be QRSS tests instead of audible CW.
On our field day 23.-25. July I will test the 800m earth base in JO30ON
(Erpeler Ley). Distance to Stefans Grabber is 160 km, to Markus 300km. Possibly
it will be my first successful far field test.
vy73 Horst DO1KHS/DI2AN.
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