[TowerTalk] How much do trees really affect verticals

[Larry Banks]

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 at 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 at 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