My QTH in central Delaware is about 12 acres with most of it a "young"
forest of loblolly pines, oak and maple that top out around 80-90 feet
tall. Prior to 1978 or so most of this was cleared farmland.
In 1998 I erected a 100-foot tower that became the (series-fed) driven
element for a 160-meter K3LR-style parasitic array. This tower was
amidst a grove of about a dozen or so loblolly pines that at the time
were about 40 feet tall. Since then they have grown to around 60-70
feet. I did make a change in the tower top-loading a few years ago that
required changing the matching at the feedpoint, but other than that
change I have not found any need to readjust the matching over time that
I would think would be needed if there was any interaction with the
trees. This antenna (3 elements to the SE/SW/NW and 4 elements to the
NE) has seemed competitive with other arrays on the band at inland
locations.
My new 4-el bs/ef tx array for ne/sw on 160 also is built in the forest
and performs well (as expected slightly more gain than the parasitic
array to the NE). These elements are only 73 feet tall and below the
treetops in that area. They are each different distances from the
closest trees yet I didn't see any significant variation in resonance of
the antennas.
One possible tree-antenna interaction I have seen is with copper ground
rods. In at least two cases where I used a large loblolly pine as an end
support for a Beverage antenna and drove in a 5-foot copper pipe for a
ground rod next to the tree, the tree later died. Loblolly pines have a
deep tap root, and copper is known to kill vegetation, so I've since
started using galvanized steel for ground rods when they need to be near
these trees.
73/Jon AA1K
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Topband Reflector
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