Re: VLF: earth antenna

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Good luck with the tests Stefan. I am not beginning to believe anything is possible!

73s
Roger G3XBM

2010/7/20 Stefan Schäfer <schaefer@iup.uni-heidelberg.de>

Dear VLF,

Today i was in the forest for more than 10 hours doing the following tests/works :-) :

Today i did my test on 8,97 and 7,97 and 6,97 kHz. It was possible to transmit on the lower frequencies like one can still see on my grabber2. The antenna current was just about 220 mA and 130mA in the 8,97 test. There were some problems with a step up transformer in combination with the big PA, thus the low current (i used a 12V/150V DC/DC converter and batteries, not my generator for high power). So the signal was even 3 dB lower than in the "73" test on 8,97 before some weeks. On 8,97 the power was 8 dB lower, thus there was no reception on 8,97 today but as we know, it works best on 8,97 in 5km distance. The lower the frequency the more i am again in the near field. This improves the propagation i suppose.

If my 5 km distance could be "utility assisted" like in Rogers tests is not sure. A wider distance reception has to be done!

After that i increased the earth antenna length to 500m, 420m ground electrode spacing!! :-) The average height above ground is still about 4m. Orientation of the antenna is N<=>S.
This was a hard work since i had to climb many trees since i had to cross 2 ways in a hight of about 6m. Since it is a conferous forest, i have 100s of scratches now but all in all it was a inspiring work :-).
I removed the far ends ground rods and will place them on the new end that will be found on thursday! Adding the last 200m part will be rather easy since there are no ways to cross any more and the tree-density is rather low ;-) Than, i will have a 700m long wire and the ground electrode distance will be about 600m!! With that antenna i will try to be received in 50km distance on 8,97 kHz when Michael Oexner is coming back from holidays in abt 2 weeks.
Before this test i will try to reduce the overall losses below 500 Ohm and do some RX tests watching the new VLF transmitter levels (DHO38 and so on).

Any bets about the signal increase when increasing the spacing from 280m to 600m?

73, Stefan/DK7FC

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