Based upon my experience using the loops of various sizes
on Field Day, there is not much point to the loop unless
it is 35 or 40 above ground, and best at 60 or better. Then,
however, I am convinced that the loop (at 50+ feet) is VERY
hard to beat as an all-purpose antenna.
Here our ground is VERY poor. Perhaps at locations where
the conductivity is better lower loops may be useful also.
I have not tried a closed-loop under the antenna or an
extensive ground system.
Perimeter wise, I think the larger the better. I have
not had much luck with triangular loops. Other odd (actually
quite odd) shapes seem to work out just fine.
All are directive one way or another on some band. No
good way to predict that characteristic, I suspect.
Feed with real open wire (short piece of "ladder line" to
get to the shack OK) and a REAL balanced tuner (Johnson
Matchbox) and the thing is a very effective antenna.
Just my thoughts. No "Science" involved. Just observations
over several years.
W4LNB wrote at length about the loop as an NVIS antenna
in a QEX column. That article might be of interest. As
I remember he advocated 0.17 wavelength as a good level
for NVIS. That would be pretty close to ground. His
work based upon models, I think.
73
K8RYU
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