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John
For your specific application short range
Underground to Above ground that seems the ideal environment for Earth mode
induction/propagation methods.
however others are distorting the facts by claiming
to be using earth mode antennas when in fact they are using grounded loops and
lossy dipoles by their own admission.
also
other factors distort the facts like enhanced
propagation along a sewer pipe route, gas mains, water mains pipes and ancient
burial grounds, bone density etc
To avoid any ambiguity I use the traditional
methods like the commercial operators and use an elevated antenna as high in the
air as possible and insulated radials for the ground plane and avoid lossy
buried ground wires.
Some years ago the buried wire earth
systems were replaced by elevated radials on ground aeronautical DF
and ground/air MF/HF installitions.
de g3kev
----- Original Message -----
Sent: Tuesday, December 14, 2010 7:49
PM
Subject: AOG antennas (was Re: LF: BODGE
ANTENNAS)
On 14 Dec 2010, at 20:10CET, Roger Lapthorn wrote:
Mal,
Please, I make no magical claims
for the earth electrode antenna I use. All I say is that, in certain
circumstances, it works rather better than one might expect both on RX and
TX on VLF/LF/MF.
For cave-to-surface communications we
have found that, in general, an earth electrode system is much better than a
tuned loop. When we tried both systems at Kingsdale Master Cave
Valley Entrance (a standard CREG test site) the earth current antenna
gave a 32 dB greater signal at the surface than did the loop.
It all seems to depend on the geology. If the top layer of the
overburden is essentially organic, then the loop tends to give better
results.
We still do not have a theoretical explanation for all this, but it
works.
John F5VLF
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