Hi Hans,
I asked QST's "The Doctor" this question a number of years ago. I have
attached a series of emails I received from a number of well known hams
below. This is the best I have ever seen. It is quite long
73 -- Larry -- W1DYJ
-----Original Message-----
From: Hans Hammarquist
Sent: Wednesday, April 09, 2014 12:08
To: towertalk@contesting.com
Subject: [TowerTalk] Fwd: Hustler 6-BTV installation
Thank you, Gary,
I have always wondered how surrounding (vertical) trees are affecting the
radiation from a vertically radiating antenna. There are (probably) as many
opinions about this (or many be more) than there are (active) radio hams.
Best 73 de,
Hans - N2JFS
-------------------------------------------------------------------------------------
From: Eugene Zimmerman
Sent: Tuesday, January 02, 2007 18:33
To: Hallas, Joel W1ZR ; Larry Banks
Subject: Re: Dear Doctor: Antennas and Trees
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://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
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 to FN53 [please do so - it is the
only grid on 2 meters within 500 miles I do not have after the advent of
grid squares - my last contact with FN53 on 2 was in 1982 with W1BJ (SK)]
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
-----------------------------------------
----- Original Message -----
From: Hallas, Joel W1ZR
To: Larry Banks
Cc: Zimmerman, Eugene W3ZZ
Sent: Tuesday, January 02, 2007 4:30 PM
Subject: RE: Dear Doctor: Antennas and Trees
I have known serious V/UHFers who had towers high enuf to clear the trees,
so it may be a problem there. Perhaps Gene has some 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
--------------------------------------------------------------------------------
From: Larry Banks [mailto:larryb.w1dyj@verizon.net]
Sent: Tuesday, January 02, 2007 4:14 PM
To: Hallas, Joel W1ZR
Cc: _Larry@ home; Straw, Dean, N6BV
Subject: Re: Dear Doctor: Antennas and Trees
Thanks Joel,
Floyd's comments agree with KF4IX's comments in Nov. '91 QST. That makes
sense to me. I would assume that horizontal branches would have to be
really horizontal and ~¼ wave to have much effect -- probably more obvious
on 10M and 20M than 80 & 40. Branches are also "usually" at about a 45º
angle, more or less, which I think would decrease the effect by 20 dB or so.
My bigger concern is VHF and UHF -- one reason I am choosing this site is
that it's in FN53, much rarer than my current FN42, and I love the VHF
contests.
I do know that trees are BAD for SHF.
Thanks again & 73,
Larry
W1DYJ
------------------------------------------
----- Original Message -----
From: Dean Straw
Sent: Tuesday, January 02, 2007 15:33
To: Hallas, Joel W1ZR ; Larry Banks
Subject: RE: Dear Doctor: Antennas and Trees
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
To: Larry Banks
Cc: Straw, Dean, N6BV
Sent: Tuesday, January 02, 2007 3:24 PM
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
--------------------------------------------------------------------------------
From: Larry Banks [mailto:larryb.w1dyj@verizon.net]
Sent: Monday, January 01, 2007 10:10 PM
To: doctor
Cc: _Larry@ home
Subject: Dear Doctor: Antennas and Trees
Hi Doctor,
I have been "lucky" in that the two QTH's on which I have been active --
Southern Connecticut in the early 60's as K1VFX and a current QTH ten miles
north of Boston -- have been on hills which have provided great upper HF and
VHF antenna opportunities with simple roof towers. The lack of trees have
meant poor horizontal antennas for 80 and 40 however. Now I am
contemplating moving to Maine to a low coastal area full of tall Pines and
hardwoods. I am wondering about the effect of trees on antennas.
Searching the ARRL site I found two references: a Nov. 1991 Technical
Correspondence from KF4IX detailing the effect of HF verticals sited close
to trees (not good) and a Dec. '85 Ham Radio article by Bill Orr, W6SAI,
which I don't have since I gave my "all-but-Vol. 1, #1" set away to a
library long ago (bad idea!) I also searched LB's web site, W4RNL, for info
on trees and found nothing. A GOOGLE search on "antennas and trees" was
also fairly useless -- about 1M citations, the early ones all about using
trees for hanging antennas.
What is the effect on horizontal antennas -- dipoles, yagis, etc. -- that
are on modest towers in a forest of tall pines and hardwoods? Is there a
difference between winter and summer -- remember, this is Maine. Is there a
difference between HF, VHF, and UHF?
73,
Larry
W1DYJ
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|