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Date: Sun, 15 Jul 2001 21:01:47 +0100
To: rsgb_lf_group@blacksheep.org
From: "Rob Gill" <rob@twickenham.freeserve.co.uk>
Subject: Re: LF: Re: Near field of 9kHz antenna IV
In-reply-to: <7D653C9C42F5D411A27C00508BF8803D55C555@pdw-mail-r1.dstl.go v.uk>
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The late John Taylor G0AKN was having some success with an earth loop 
antenna at audio frequencies in 1999 (-albeit without the assistance of an 
NOV!).

With an transmitting earth base of  several hundred metres and a receiving 
earth base of 200m he transmitted slow CW at 6kHz over a distance of 6.6 
miles. Details can be found on his web site which remains 
at  http://www.wireless.freeserve.co.uk/

Sadly his illness precluded further work at these frequencies although it 
seemed likely that much greater range was possible provided that a low 
noise receive site could be found. Even in rural areas noise pick up from 
power lines seems to be a big problem at these frequencies.

Earth current antennas of this type have also proved effective in LF cave 
communications, yielding significantly better results than the small multi 
turn inductive loops which earlier cave radio designs employed. DX is a 
relative expression however! Communication over ranges in excess of 
500metres is considered pretty good -though that is through rock.....

73
Rob
G8DSU
.................


At 09:43 16/07/01 +0100, you wrote:
>For our garden sized antennas I think that resonating a wire is completely 
>impractical at these frequencies.  What I intend looking at, (if a 9kHz 
>NoV ever happens :-(   is something like a ground loop.  I'm basing the 
>idea on the US Submarine comms experience at ELF / ULF. (Have a look on 
>the web at Project Sanguine I think its called)   If a really long wire is 
>laid out at low elevation - just lying on the ground even - then fed 
>against a real earth connection then a ground loop will be set up.  There 
>will probably not even be a need to ground the far end.   With a skin 
>depth, particularly in low conductivity ground, measured in 10s or 100s of 
>metres then quite a large loop will result.
>
>I know ground loops were tried on 73kHz, with only moderate sucess, but 
>the much lower frequency ought to improve the efficacy of the 
>system.   Even in my urban plot, it will be possible to lay out several 
>hundred metres of wire by just trailing it over the garden wall and along 
>a grass verge by the road.   I'll be limited in wire length only by 
>roundabouts where the verge stops.
>
>Andy  G4JNT
>
>>>>The corrected figures are even more dramatic than for the loop.
>>>>
>>>>To feed 1kW into the 180m high 15mm copper pipe the current must be 
>>>>154A and the voltage on the antenne becomes 2.5MV! Perhaps the pipe 
>>>>would survive the current but the voltage makes the system completely 
>>>>unrealistic (corona).
>>>>
>>>>And what would the required 286mH loading coil for that voltage and 
>>>>current look like ...
>
>
>--
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