Hi Gary and all, no cans of worms....we are all just trying to understand
what is happening with our non-commercial sized aerials .....and trying to
avoid any of the old wives tales. It is interesting that Laurie lives in
Bosham. Look at his QTH on the map and you would not believe he has trouble
with ground resistance. However Laurie has fought hard and long to get the
loss resistance down. Finbar lives alongside a sea-water bay, and he has to
do considerably more than just shoving a spike in the ground. Most perople
assume that seawater is a good conductor, it is better than land, but it is
not that good otherwise LF radio waves would not penetrate it to be used by
subs.
It is a very complex problem and I would be glad for anyone to explain the
test results we have measured. I have yet to do the experiment of playing
the hosepipe on the ground under the aerial on an otherwise dry day to see
what difference it makes. The other problem is that my tap-water is almost
saturated with calcium carbonate so not as low a resistivity as rain-water.
( I am also metered and mean....but we wont talk about that )
There is an interesting reprint in the back of the newer LF Experimenter'
Handbook written by a German engineer about experiments at Nauen in 1922. I
think a lot of his results are pertinent to this question but he does not
hazard an explanation beyong the equivalent circuit with a lossy
capacitor.!! I said he was an engineer !! I am about to return to Watt's VLF
Engineering to see what can be gleaned from the extensive chapter on
earthing there. Also there is a book by Sunde which is devoted to earthing,
but more from the point of line transmission.
Most Garden Centres will sell you a soil moisture meter where the resistance
drops with increasing "wetness" ....these dont operate at 136kHz ,
unfortunately.
Great fun, and highly important as ground loss is the biggest of our
problems, half the ground loss, and you double the aerial current and
quadruple the ERP......and the worms dont get quite so much "central
heating".
Cheers de Alan G3NYK
[email protected]
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