To: <towertalk@contesting.com>
> Date: Wed, 06 May 1998 12:50:40 -0400 (EDT)
> From: W7NN <W7NN@aol.com>
> I've never seen a study on resonant trees but maybe others have experience
> with this area.
>
I got "roped into" measuring the resonant frequency of tree by some
guy who thinks they make great antennas because they are shaped like
(gag) fractals..
In order for a tree (or any other conductor) to be resonant, it must
be a pretty good conductor. Since I can't jump start my car with tree
trunks, I had doubts as to the validity of actual resonance.
I measured thousands of ohms per foot in a fresh pine tree
with just over one foot of cross section, the tree could not
possibly be resonant with that much series resistance.
Even with such a high RF resistance I can't discount the possibility
each tree absorbs a tiny bit of energy. Roy Lewallen W7EL (a
VERY reliable engineer) mentioned he felt a very thick stand of trees
attenuated his 7 MHz signal a measurable amount, but the data was a
bit shaky and more tests needed to be made.
In my open pastures ( on a ridge top, this is a "cow farm"
and has many hundreds of feet of flat open pasture near the antennas
before reaching any trees), a 7 MHz vertical doesn't work nearly as
well as a high dipole for DX. A 3.5 MHz vertical ties a 110 foot high
dipole consistently for DX, even when in the middle of trees. My
160 verticals work excellent, and blow away a 180 ft high dipole.
I suspect that verticals just don't work well when frequency is
raised much above 80 meters. Anyone else have any thoughts on that??
The trees probably don't help either, but they don't seem to hurt 80.
(The trees that used to surround my 80 vertical were all about 70 to
100 feet tall. I would think that a bad height for 80 meters, yet
they didn't seem to hurt the antenna performance at all)
Has anyone ever seen actual properly measured and documented data on
this?
73, Tom W8JI
w8ji.tom@MCIONE.com
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