Hi Jim you cant really calculate these thing s becayuse there are just to
many varibles. The only way it to measure the loss of the untuned aerial
with and rf bridge and then measure the same format out in the open...same
ground same weather same season etc etc. The Yanks put their aerials through
the trees because they use loops and the voltage on the wires in many order
lower so the current lost to the tree is much smaller. (I think) Jim Moritz
used to have some dramtic measurements taken on 136kHz before and after
pruning his "aboretum" May thumbnail approack says put a vertical at least
as far away from trees, walls, roofs etc as it is high. Not aways easy!
Alan G3NYK
----- Original Message -----
From: "James Cowburn" <[email protected]>
To: <[email protected]>
Sent: Sunday, November 08, 2009 3:19 PM
Subject: LF: Losses due to ant in tree?
> 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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