I have been reading all of these posts and feel perhaps I can add to the
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:
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
Joel R. Hallas, W1ZR
Technical Editor, QST
American Radio Relay League
...and the response from Dean Straw:
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!
Senior Assistant Technical Editor, ARRL
Editor, The ARRL Antenna Book
...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.
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.
73 Gene W3ZZ
World Above 50 MHz
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:
The July 2008 QST "Doctor Is In" has the final response to my question.
73 -- Larry -- W1DYJ
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