Jim, it seems to be a difficult subject for those who want to make a huge
case out of taking measurements as if this was a scientific undertaking
requiring a decade of reviews, papers, and the usual academia way of wasting
time.
For the rest of us ancedotal evidence is often sufficient...if the tree or
parts of it died coincidental with installing an antenna or increasing ERP
then that is good enough IMO. Others can hire an arborist and a passle of
investigators from the County Extension who just might take you to court
along with a screaming horde of tree huggers demanding your scalp (-;
Foliage induced attenuation without obvious damage is another subject all
together. That will vary by the tree, climate, phase of the moon and when
the dog last peed on it. And like the perennial discussion on
grounds....everyone has an opinion and different circumstances.
Carl
KM1H
----- Original Message -----
From: "jim rogers" <jdrog@bellsouth.net>
To: "ZR" <zr@jeremy.mv.com>
Cc: "Topband" <topband@contesting.com>; "Rudy Severns" <rseverns@gmail.com>
Sent: Monday, August 05, 2013 9:03 AM
Subject: Re: Topband: tree losses
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
_________________
Topband Reflector
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1432 / Virus Database: 3209/6051 - Release Date: 08/04/13
_________________
Topband Reflector
_________________
Topband Reflector
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1432 / Virus Database: 3209/6052 - Release Date: 08/05/13
_________________
Topband Reflector
|