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Date: Fri, 04 Jun 2010 18:30:41 -0500
From: "Mike.WE0H" <we0h@gmx.com>
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Subject: Re: VLF: 2km on 8,97 kHz using 6W TX power and a 120m earth antenna
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Hi Roger,

Could you show me a picture or describe your Earth Electrode antenna? I 
have all heavy trees here so no other antenna would likely work. What 
feedline? What wire size and what length of the electrodes? Does the 
wire run straight away from the feedline in opposite directions to the 
earth electrodes or?

Thanks much,
Mike
WE0H



Roger L wrote:
> Stefan,
> 
> A few observations on your tests using the earth electrode "antenna" today:
> 
>    1. In my experience, most of the signal transmission is by induction,
>       so I think it would be worth trying to receive the signal with a
>       loop antenna when the received signal may be much stronger than on
>       the E-field probe. In my case I use a 30turn, 80cm square, loop
>       which can be rotated to minimise 50Hz interference.
>    2. On my 10m and 20m baseline earth electrodes I was measuring
>       resistance of between 40-60 ohms between 1-9kHz, so your figure
>       seems very high. This may be as a result of the soil and rock type
>       in your area but this is worth checking. If my theory of the "loop
>       in the ground" is correct then a poor conductivity soil would
>       result in a larger effective loop area within the ground.
>    3. Did you try matching the PA to this high impedance through a
>       transformer? I think not in this test, so better results may well
>       be possible.
>    4. Regarding Mal's comment about "you need a 100m high antenna", well
>       you know this works, but the point of this experiment is to see
>       how effective, or not, an electrode "antenna" is. The results are
>       valuable whether good or not.
> 
> Here, I have completed a further "by ear" range test using my TDA2003 4W 
> PA into a 20m base electrode pair "antenna" walking around the village 
> in many different directions using the 80cm loop RX at around 1.5kHz. I 
> improved the 50Hz rejection this week by adding another Sallen-Key HPF. 
> When walking over metal pipework in the roads the signal is strong up to 
> at least 0.25km in almost any direction and limited by 50Hz noise. When 
> walking across fields well away from pipework the loop orientation 
> exactly lines up with the base electrode "loop in the ground" at 
> distances up to 0.5km.  I have not managed to hear the signal at any 
> further distance in any direction. My grandson is back staying with us 
> all next week, so very limited chance for more experiments until about 
> June 14th. I have a long list of things to try still!
> 
> 73s
> Roger G3XBM