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LF: Re: Proximity effects

To: [email protected]
Subject: LF: Re: Proximity effects
From: "mike.dennison" <[email protected]>
Date: Sun, 22 Sep 2002 11:36:36 +0100
References: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
Steve Thompson wrote:
I'm struggling with a poor set of options for an aerial at this house. The
greatest vertical section I can get while still allowing top loading is
8-9m, but the lower 3-4m would be up against brickwork. How much does this
affect radiation compared with, say, 6m vertical clear of buildings (with
the same toploading)?
It depends what you mean by "up against". Good insulation is vital, but
assuming you mean 100mm or more separation, there should be little problem.
There are two things you can do to improve things:

1) Use an inductor above the brickwork (as high as is practical) to reduce
the voltage close to the lossy structure.

2) Run an earth wire up the brickwork, connected at the bottom to ground.
This will give you a fixed capacitance to earth, rather than a changeable
resistor (the bricks).

My antenna is about 2 metres from the house brickwork for the first 8m of
the 14m vertical span. It is attached to a metal mast bolted to the wall
with 600mm metal stand-offs (see http://www.f.thersgb.net/antenna.htm).
Earthing the mast did not reduce the effectiveness, but made the current
much more stable from day to day.

Go for it.

Mike, G3XDV
http://www.lf.thersgb.net
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