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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