I am absolutely convinced that tall trees next to a low band vertical have a
very negative effect on my radiated signal. For the past 11 years, I have had
the opportunity to live on 3 acres of land with trees strategically located so
that they shield the view of my 80 foot tower from the public. The positive is
that I have not had to deal with building permits or variances to put up an
effective antenna system for both the low bands and the upper HF bands. A TH6DX
currently sits on the tower as a capacity hat and I have 30 quarter-wave
radials under the shunt fed tower (fed at the 47 foot level with 75 ohm
hardline).
My tower is surrounded on three sides with tall oak, maple, popular, and ash
trees most of which are higher than the tower. What I have noted over the past
11 seasons is that when the trees are fully leafed out which is from late April
until late October, both the match and bandwidth of the tower is affected. The
bandwidth is much broader from 1800 to 1900 during this period.
Performance-wise, it is an issue. It is much harder to work DX and my signal
reports are down from one to two S units.
Once the leaves are gone, I speculate that something happens to the water in
the trees in early to mid-November. The SWR rises and it becomes necessary to
retune the gamma match on the shunt-fed tower. Performance then seems to be
great on the vertical and I have no problems working EY8. UA9, VQ9 etc.
If I had to do it over again, I would have put the base and tower in a location
further away from these tall, old trees. It also seems that the HF beam is
affected by the leafing out of the trees in the Spring, and loss of leaves in
the Fall, but not as severely as the shunt-fed tower.
73, Dennis W0JX/8
Milan, OH
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160 meters is a serious band, it should be treated with respect. - TF4M
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