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Re: LF: Earth antennas, Beverages...

To: [email protected]
Subject: Re: LF: Earth antennas, Beverages...
From: Stefan Schäfer <[email protected]>
Date: Wed, 11 Apr 2012 18:05:40 +0200
In-reply-to: <[email protected]>
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Hi Alan,
Am 11.04.2012 17:23, schrieb ALAN MELIA:
Interesting Stefan........though I am not sure it is actually working as a Beverage, They are usually quoted as being between a  half and one and a half wavelengths long
Yes, sri, the word is wrongly used here. I think the name is used since amateur stations use such an antenna on HF too, where it acts as a beverage. On LF it is to short to use that name.

73, Stefan

.....but they are travelling wave antennas. Marconi stations used to lay out an insulated with on the ground about 5 to 10 km long in the direction of the transmitting station. This had no "effective height" at higher frequency interference, whereas the skin depth was significant particularly in "poor" ground at VLF.  My "take" is that they are all coupling loops, coupling to the Earth Ionosphere waveguide.....in essence the K9AY works the same way I think. Termination makes them unidirectional. Loads to play with :-))

Alan
 

--- On Wed, 11/4/12, Stefan Schäfer <[email protected]> wrote:

From: Stefan Schäfer <[email protected]>
Subject: LF: Earth antennas, Beverages...
To: [email protected]
Cc: "Dimitrios Tsifakis" <[email protected]>, "Bob" <[email protected]>, "Edgar J Twining" <[email protected]>, [email protected]
Date: Wednesday, 11 April, 2012, 14:12

Hi David,

Sorry for my late reply about your beverage antenna mail.

Thanks for your point of view to the beverage antennas and the pictures. That sounds all very interesting and i can imagine about the high signal levels coming from such a antenna. The problem in Germany is o find a place which is far away from man made noise sources and allow to hung up such a long wire.

But i have found such a place! :-) However i didn't spend much time and interest to it regarding receive possibilities. I'm just getting re-inspired by thinking of it. It is in a very quiet location!

In the forest of Heidelberg in JN49IK77 i hung up a 700m long wire. It is called my earth antenna. The main intention is and was to transmit on VLF on this antenna. The far end is grounded by 20 or 30 earth rods, 40cm deep and about 1m separated. The same on the other end. This forms a loop where the current flows back through the earth. The lower the frequency and the lower the ground conductivity, the deeper the return path of the current, so the bigger the cross section area and the higher the efficiency.
That region is a hill/mountain about 500m ASL and 400m above the local ground in some km distance. The ground is out of stone with a layer of soil, about 30cm. The need for a poor ground conductivity stands in opposite to the wanted low loop resistance, which means the need for high effort on the grounding at each end, i.e. a high number of ground rods. Also the wire length is very important.
Anyway the efficiency will be poor but anyway you have a most seldom and interesting transmit antenna whioch is not resonated, thus it is possible to transmit on any frequency. I'm also looking forward to the 500 kHz allocation. It will be nice to use it as a receive and transmit antenna on 475 kHz.
In summer when it is dry i achieved a loop resistance arround 800 Ohm, which is coming from the grounding losses dominantly. I've done several transmit tests and achieved 35 dB S/N in 4.5 mHz in a distance of 5 km, to my own VLF grabber.
During the first times where the antenna was still shorter a wrote a short report with some pictures: http://dl.dropbox.com/u/19882028/VLF/VLF_5km_with_an_earth_antenna.pdf
Tests with Michael Oexner (SWL, NDB hunter) in 49 km were positive too, in DFCW-600, see the attached Mail from 2010. BTW this is a VERY good demonstration of the positive effect of band limiting, clipping and noise blanking of the VLF signals processed in SpecLab. The picture shown my signal with and without the SpecLabs noise reduction technics. This 49km distance in 4.5 mHz  is the current record with an earth antenna. The transmit power was 200...250 watts if i remember correctly.

I will check if the antenna still exists and will refurbish it. Also i will do new tests there. BTW i've done a recording on VLF using this antenna in January, 29th 2011, if someone wants to play with it (1 GB): http://dl.dropbox.com/u/19882028/VLF/29012011_12UTC_earth%20antenna_recording.WAV

In VK it seems you can easily arrange such an antenna, maybe even across a stony hill and grounded into the sea at one end. You just need some wire and a portable PA :-) BTW this is the PA i was using: http://www.iup.uni-heidelberg.de/schaefer_vlf/12V_300W_VLF_PA.pdf

73, Stefan/DK7FC
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