In a message dated 96-12-15 00:54:00 EST, you write:
>
>I use a wire vertical that is suspended from a pine tree limb 92' above
>ground. The tree is 120', or so, tall. The antenna is about 3 or 4 feet
>from the trunk. On 160, the antenna operates as a 90' top loaded vertical
>(capacity hat), and on 80 it operates as a quarter-wave vertical. I have
>about 15,000' of radials of various lengths .... 30' to 400'
The primary problem would be the nearfield coupling via the electric field to
the tree.
It's like a "capacitance problem" in this case, rather than a radiation field
problem. The problem would be worse with a big bushy tree that occupies a lot
of physical area, rather than a less leafy pine.
One solution would be to build a cage of in-phase wires (use at least two,
one on each side of the tree) with symmetrical (to the tree) top loading on
each wire and to eliminate the E- field in the tree.
If the high voltage portion of a single wire antenna is in or near the tree,
losses would be higher. Insulation won't help this problem, because it is
"capacitive coupling". Distance (spacing) will help it only when the distance
change lowers the electric field (displacement currents) crossing the tree.
Think of this like a capacitor problem, and the tree is a lossy dielectric in
the E-field. If the electric field is strong and spread out over a large
area, like it is near the high voltage end of the antenna, and the tree
occupies a large area of that area, losses would be higher.
I have no idea how large the loss would be, since I don't know the dielectric
properties of the tree. My antennas in or very near pine trees also seem to
work OK for me. I keep them away from Oak trees.
73 Tom
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