I cant think of anyone claiming a tree is resonant on any particular
frequency but that doesnt mean it cant be used as an antenna. Anyone
disagreeing with that should discuss it with the military who have been
loading trees for decades for emergency communications; in the 3-8MHz range
if I remember and going back as far as the 50's. Read the old CQ and QST's.
On another note I spent most of today outside doing tree trimming and other
sweaty exercises. I noted that my best producing Bartlett pear tree was dead
at the top and also a bit down on one side. Now it may be just coincidence
but the 80M sloper passes about 5' from the farthest out branches and the
end is exactly at the same height as the tree top.
This antenna is used at the vintage gear bench and also on the one for amp
repairs where Ive been hitting it rather hard this year with AM with serious
carrier power; the most recent being an Alpha 77SX.
I also remember wilting the top of a sugar maple about 20 years ago with
1200W on 6M to a 6/6 yagi array. After I moved the antenna to another tower
the tree recovered the following year.
Another coincidence?
Carl
KM1H
----- Original Message -----
From: "Rudy Severns" <rseverns@gmail.com>
To: "Topband" <topband@contesting.com>
Sent: Sunday, August 04, 2013 5:39 PM
Subject: Topband: tree losses
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.
73, Rudy N6LF
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