Message-ID: <20091108163840.lo5b6gea88oc448g@webmail6.kuleuven.be>
Date: Sun, 08 Nov 2009 16:38:40 +0100
From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
References: <001b01ca6086$cd0966b0$0617aac0@jimdesk>
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Subject: Re: LF: Losses due to ant in tree?
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Hello Jim,

my antenna is surrounded by numberous birch and oak trees. 4 of them =20
in fact act as antenna support.
As a result I have a relately high antenna loss: 130-200 Ohm on 137kHz =20
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 =20
and the greenery. I would recommend not to go much closer to avoid =20
extra losses and certainly not touch branches (not even with isolated =20
wire) as with high voltages this could start a fire due to arcing.

73, Rik  ON7YD - OR7T

Quoting James Cowburn <james.cowburn@virgin.net>:

> Hi All,
>
> The vertical 5m section of my inverted L runs up into the branches  =20
> of a silver birch tree.  The wire goes over a large bough at 5m or  =20
> so and then comes out of the branches for some 22m down to a 4m high =20
>  pole attached to the garage.
>
> Has anyone a guesstimation of the losses in signal caused by running =20
>  the wire through the tree?
>
> Using vertload and tophat2 I calculate the antenna to be around  =20
> 0.25% efficient but this assumes it is in free space.  Can anyone  =20
> suggest a figure for the additional loss due to tree heating!
>
> The vertical element is actually sloping at about 20 degree from the =20
>  tree down to the loading coil.  The length is nearer 6metres but =20
> 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  =20
> mark 2, well away from the silver birch!)
>
> With best regards
>
>
> Jim
>
>
> Dr. James Cowburn G7NKS
>