Hello Jim,
my antenna is surrounded by numberous birch and oak trees. 4 of them
in fact act as antenna support.
As a result I have a relately high antenna loss: 130-200 Ohm on 137kHz
and 45-70 Ohm on 500kHz (low values in winter, high values in summer).
I try to keep a distance of at least 2m between any "hot" antenna wire
and the greenery. I would recommend not to go much closer to avoid
extra losses and certainly not touch branches (not even with isolated
wire) as with high voltages this could start a fire due to arcing.
73, Rik ON7YD - OR7T
Quoting James Cowburn <[email protected]>:
Hi All,
The vertical 5m section of my inverted L runs up into the branches
of a silver birch tree. The wire goes over a large bough at 5m or
so and then comes out of the branches for some 22m down to a 4m high
pole attached to the garage.
Has anyone a guesstimation of the losses in signal caused by running
the wire through the tree?
Using vertload and tophat2 I calculate the antenna to be around
0.25% efficient but this assumes it is in free space. Can anyone
suggest a figure for the additional loss due to tree heating!
The vertical element is actually sloping at about 20 degree from the
tree down to the loading coil. The length is nearer 6metres but
the vertical height over ground at the bough is about 5m.
(Santa may be bringing me a set of swaged poles with which to build
mark 2, well away from the silver birch!)
With best regards
Jim
Dr. James Cowburn G7NKS
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