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Re: LF: RE: Summer games / EARTH ANTENNAS

from [Roger Lapthorn] [Permanent Link][Original]
To: "[email protected]" <[email protected]>
Subject: Re: LF: RE: Summer games / EARTH ANTENNAS
From: Roger Lapthorn <[email protected]>
Date: Tue, 10 Jul 2018 12:10:40 +0100
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Dear All,

As I have been away for a few days let me say a few words.
  • Yes, I agree that a "decent" antenna and ground system will outperform an "earth antenna".
  • Certainly at 472kHz I have been amazed how well an earth antenna works. In the autumn and winter seasons I reach over 1000km to Norway quite regularly with 5mW ERP using mine with WSPR.
  • My "baseline" is only about 12m, so not long at all. 
  • The earth connections are about 1m rods driven into the soil.
  • Interconnecting wire is multi-strand hook-up wire. I think it is 32 x 0.2mm.
  • At the old QTH it was a good match to the transverter at 50 ohms. At the new QTH it is better with a 3C90 step-up transformer. This implies a higher resistance at the "new" QTH. We have now been here almost 5 years!
  • In my view the "earth antenna" works as a loop at 472kHz and 137kHz. I have not had good results at higher frequencies.
  • As a "compromise" antenna it is worth trying.
  • With low conductivity soil or rock the loop size would be bigger.
  • Magic? No!
  • Radiated VLF? No idea. I suspect it would work as the skin depth would be better as you go lower in frequency.
Let us hope this input is useful. Never say you don't have space for a 472kHz antenna!

73s
Roger G3XBM


On 6 July 2018 at 09:15, DK7FC <[email protected]> wrote:


Am 04.07.2018 18:51, schrieb VIGILANT Luis Fernández:

Mmmm. Kite antennas are for summer ;-)


 What? Ehm, no. They are for winter! :-)
See: http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/300m%20VLF%20kite%20vertical.jpg

Helium is much to expensive and you can use the baloon just one time, then you have to release the gas again. This is not practical! And if there is strong wind, the baloon is not very stable, expect you make it much larger than necessary, so there is a strong force on the wire.

A kite however can stay stable in the air for hours! Once i kept it in the air (including a 100m wire connected) for > 24 hours. Everyone (even if retired!) can buy a kite and some string and rise it somewhere :-)

73, Stefan

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