What may be of more effect is the seasonal effect that forestation has on
the water content of the ground by roots passing water on to the leaves for
evaporation. The cooling effect of this evaporation is the source of the
early evening cool air out of the woods once the sun is down. This
materially ceases once the leaves are down.
Ask someone who has had a tree growing next to their house. With a
foundation in ground with some degree of clay, cracks appear in a foundation
due to ground shrinkage by the tree evaporating ground water through its
leaves.
When the leaves go down, the ground stays wetter and the RF charactistics of
the ground change.
73, Guy.
On Wed, Nov 4, 2009 at 11:46 AM, Dennis W0JX <w0jx@yahoo.com> wrote:
> 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
>
>
>
>
> _______________________________________________
> 160 meters is a serious band, it should be treated with respect. - TF4M
>
_______________________________________________
160 meters is a serious band, it should be treated with respect. - TF4M
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