Message-ID: <000e01c25ef4$877024e0$636868d5@oemcomputer>
From: "mike.dennison" <mike.dennison@ntlworld.com>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 18 Sep 2002 10:19:43 +0100
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Subject: LF: Capacity hat puzzle
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My antenna failed recently because one of the leads to the elevated loading
coil had broken. To fix it I had to lower one of my 14m masts - a task
requiring several people so I don't do it very often.

Whilst the mast was down I modified the capacity hat. There are three 17m
long parallel wires, about 0.5 metres apart (total span 1m). The wires are
joined at both ends. (See http://www.lf.thersgb.net/antenna.htm for a
picture).

I changed this so that the wires were only joined at the far end. Now the
vertical wire and the elevated coil are connected to the centre wire only.
The RF travels along this centre wire to the end, then back using the outer
two wires in parallel..

I expected this to increase the inductance of the antenna and so lower its
resonant frequency. The actual effect was the opposite - the frequency
increased and I had to add inductance at the base of the vertical.

Any thoughts?

The next time I lower the mast, I will restore the connections.

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