Larry and Roger,
I also read the QST piece with interest, and I agree with Roger and
mostly with Gene -- it's a limited, but useful analysis, and I don't
find any holes in it as far as it goes. BUT -- making the tree in the
model approximately resonant certainly could affect things, and probably
simulates worst case.
It is important to realize that this analysis assumes a vertical
antenna. My station is in a clearing within a dense redwood forest. My
only verticals are for 160M; one is a 105 ft Tee over about 60 on-ground
radials. I tried an 80M quarter wave over the same radials and found it
to be quite a bit less efficient than a dipole at 120 ft (since raised
to 140 ft).
I've studied the Tamir references, which someone was kind enough to send
me. One of the papers includes a fine analysis of propagation through a
forest, but requires knowledge of the dielectric properties of the
trees. It suggests that horizontally and vertically polarized waves
would be attenuated. And all the serious work I've seen published says
that absorption increases with frequency.
My primary antenna above 30M is a 3-el SteppIR at 120 ft, which puts it
at least 80 ft above the tops of the trees. It plays well on all bands,
even to the extent of allowing me to work meteor scatter on 6M. I also
have monobanders for 20, 15, and 10 at heights of 20-40 ft, and there's
a long horizontal 2M Yagi a few feet above the SteppIR. I have the
sense that the trees ARE absorbing some of the signal, but probably less
than the terrain effects of being 200 ft below the top of a ridge to the
east, and 500 ft below the top of a ridge to the north-northeast. :)
The advice I strongly disagree with is to avoid property with trees.
They make great supports for wire antennas, and they provide a visual
screen that often makes the antenna less visible. If you're in a
situation where a tower is impractical, a tree or two can be a real
blessing!
I'd love to read the Longley paper, but the link below doesn't come up
for me.
73, Jim K9YC
On 2/7/2018 8:16 AM, Larry Banks wrote:
The best reference I can give is section 2.3 [on p. 18] in a 1978
paper by A.G.Longley at the U.S. Dept. of Commerce.
http://72.14.205.104/search?q=cache:IEqG7929jj4J:www.its.bldrdoc.gov/pub/ot/ot-78-144/complete_report.pdf+radio+wave+attenuation+trees+HF&hl=en&gl=us&ct=clnk&cd=22
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