I hope all of us can keep the topic at least somewhat scientific, logical,
or rational, and less subjective, blind faith, or outright
off-the-wall..........
Tom's correct, the issue is not "resonance" but rather what, if anything,
happens when you have a so-so conductor/insulator (a tree) in the
near-field and/or further out. Do the losses matter?
Performing a definitive set of experiments would be a serious undertaking.
I've fiddled around a bit but not much more than the tree conductivity
work mentioned earlier.
At this point I'm an agnostic: we really don't have good data. There are
a number of Vietnam era papers on trees as antennas and propagation
through jungle but most of that was at frequencies well above 160m.
Here's a challenge for experimenters that'll keep you busy and out of the
bars.
I've wanted to catch logging operations around here and make field strength
measurements before and after trees are removed. Unfortunately I've always
been busy at the wrong times to click with tree removal, or the weather has
been a factor. It wouldn't do much good to measure FS if one reading is in
rain, and the other is in dry weather, unless a few unchanged path readings
were taken to normalize the system.
My general thought was to read absolute signal levels between TX antennas
here and a remote fixed antenna on the other side of tree removal, with
another reference point outside the removal area as a standard. But then,
even if we know that, I always wonder what good it does. Foliage hundreds of
feet. let alone miles away, is out of our control.
As for trees being "antennas", that would be a simple experiment. One could
simply try to "load the tree", however that might be accomplished, and
compare the signal level with the same size loading system (properly
rematched) without the tree. Several reruns with different trees could give
a baseline.
I think the reason that has never been done is most people who understand
losses and radiation also understand the few feet of wire in the matching
system is probably the major radiator in the system, so there is very little
interest in proving the obvious. Most of us already understand an insulated
copper wire thrown over a tree is a far better antenna than the tree could
ever be, and that removing the tree actually INCREASES field strength. The
logical conclusion is the tree is much more a dissipative load than an
antenna. After all, if a tree was even a marginally effective LF or HF
radiator, we would increases in field strength from reflections rather than
just absorption.
At some higher frequency there are measureable echoes, but they pale
compared to the incident wave. Remember the moon, as horrible a conductor as
it is, still has useful reflections when the illumination is over a wide
surface area.
In the real world, it often isn't a case of if something is or isn't, like a
toggle switch being on or off. It is often a case of how much it is or
isn't. Some things that are way over in the "isn't meaningful" column get
publicity as being "is", just because they are not perfectly zero or
infinite.
73 Tom
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Topband Reflector
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