Carl et al,
Interesting, my 80M full size (66') sloper comes within about 5 ft of a
dogwood tree and it is dying. The sloped is fed 8' AGL with 2 full size
elevated radials and about 500w and the dogwood is dying from that
height(8') to the top of the tree at about 15'. Unfortunately for me, my
XYL pointed this out to me - not good. The sloper has been in that
position for about 1 year, before that the tree was doing fine.
Coincidence?
Jim N4DU
On 8/4/13 9:42 PM, ZR wrote:
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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