Hi Gregg,
I asked this same question a couple of years ago -- of the QST's "The
Doctor Is In." Here are the answers I received.
73 -- Larry -- W1DYJ
------------------------
Hi Joel and Larry
Everyone appears to have an opinion on this subject but definitive
scientific works are more difficult to find - at least on the Internet.
From a practical observational standpoint, I have found that low band
verticals particularly 80 and 160 do not seem to be bothered by deciduous
hardwood trees. However I used these during contests that occurred mainly
in the colder months though I am reasonably sure that the sap has NOT
drained by the end of October and I never noticed a difference between
late October [leaves have turned but half of them are still ON the trees]
and February [leaves gone and sap drained if it really does drain in MD].
My station has all its yagi antennas mounted on a 24 ft mast beginning on
top of an 83 ft tower on a 1/4 acre lot. The good news is that the tower
sits at the edge of a group of hardwood trees so it is nearly invisible in
spite of its size. The bad news is that the trees, once 70 ft tall are now
approaching 90-100 ft range. I don't think the trees bother my HF
tribander at 83 ft. Or my 7 el 6 meter beam at 87 ft. But the 2 meter beam
at 95 ft may be impacted. I think my 2 m signal on moonrise/moonset EME is
at least 3 dB below what it should be. I also think that at 432 and
above -especially above- trees are bad news [see below].
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://www.its.bldrdoc.gov/pub/ot/ot-78-144/ot-78-144.pdf >
That paper and others that I have found agree that avoid trees entirely is
the best course. Anything at 100 MHz and more is unacceptably attenuated
by trees with non-deciduous pine trees being somewhat worse than deciduous
hardwoods. At HF the effect may be quite a bit less noticable. Verticals
at HF may be more affected but again the difference is only a very few dB
more. Pine trees at HF are worse for the reasons you have already noted.
Therefore I would say if you are moving ... you need to take the dense
tree cover seriously. On 2 meters you will be impacted and above 2 meters
unless you are clear of the trees you may be severely impacted. I suspect
on 160 - 40 meters you won't have much trouble but a tribander buried in
the trees is also likely to see some attenuation - maybe more than you'd
be comfortable with. The same with 6 meters. For less dense trees I think
the tribander and 6 meters would be o.k.
Good luck.
73 Gene W3ZZ
World Above 50 MHz
FM19jd MD
50 => 10 GHz
Grid Pirates Contest Group K8GP
Member, CQWW Contest Advisory Group
----------------------------
Hi, Guys:
My understanding is that you'd have to put a vertical radiator very close
to a tree for sap/no-sap to have any impact on the antenna's
performance -- perhaps within a foot of the trunk. Having said that, I
know of several hams who did very well with "disguised, stealth" vertical
wires run right up alongside the trunks of substantial pine trees. These
gents worked lots of DX with such setups. Of course, YMMV!
73 and HNY,
Dean, N6BV
Senior Assistant Technical Editor, ARRL
Editor, The ARRL Antenna Book
-----Original Message-----
From: Hallas, Joel W1ZR [mailto:W1zr@arrl.org]
Sent: Tuesday, January 02, 2007 12:24 PM
To: Larry Banks
Cc: Straw, Dean, N6BV
Subject: RE: Dear Doctor: Antennas and Trees
-----------------------------------
Larry,
I haven’t seen definitive words on the topic, however I believe trees have
more of an effect for HF signals on vertically polarized signals then on
horizontally polarized ones. Floyd Koontz, in his Horiz Ewe article in Dec
06 QST asserts that sap flow makes a difference and that if the sap drains
in winter there is less of an effect on signals. This makes some sense,
although I’m not sure why trees with wide branches wouldn’t have similar
effect on a horiz component.
I am copying ARRL Antenna Book editor Dean Straw, N6BV, in case he has any
thoughts,
Regards, Joel
Joel R. Hallas, W1ZR
Technical Editor, QST
American Radio Relay League
The national association for AMATEUR RADIO
TuTh; 860-594-0393
MWF; 203-226-7353
-----Original Message-----
From: k9kl
Sent: Sunday, August 24, 2014 22:22
To: TowerTalk@contesting.com
Subject: [TowerTalk] How much do trees really affect verticals
I have been clearing some land to plant more maple trees for my sugar bush
to make maple syrup in the spring. While I resting I thought of all the
room I am clearing for a 4 square for 75/80. There are 40 some deciduous
trees on the land which is about 150 feet by 350 feet. Prime farmland,
stream bottom with about 4-5 feet of topsoil. Its about 200 feet from my
house/shack.
How much are those trees really going to affect the antennas?
Gregg K9KL
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