[TowerTalk] trees and verticals

[Larry Banks]

I have been reading all of these posts and feel perhaps I can add to the 
conversation.

Back in 2007 I was looking at property on the coast of Maine -- with tall 
trees.  I was also curious about the effect, so I sent off a question to 
QST's "The Doctor Is In," not really expecting too much.  I was very 
pleasantly surprised at the ensuing email "back-and-forth" between various 
people in Newington and me!

        Here is the response from Joel Hallas:
------------
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
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        ...and the response from Dean Straw:
------------
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,

Dean, N6BV
Senior Assistant Technical Editor, ARRL
Editor, The ARRL Antenna Book
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    ...and the response from Gene Zimmerman:
------------
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

------------

If I remember, the URL for the paper may no longer be a good one, 
unfortunately.  This link is the same paper:
http://www.its.bldrdoc.gov/pub/ot/ot-78-144/ot-78-144.pdf


The July 2008 QST "Doctor Is In" has the final response to my question.

73 -- Larry -- W1DYJ