Message-ID: <21031.200102151453@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Thu, 15 Feb 2001 14:57:59 +0000
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Subject: LF: Insulator problems
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Reply-To: rsgb_lf_group@blacksheep.org
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Dear LF group,

I notice a few people have been having problems with insulators 
melting/cracking lately. I had problems with my insulators until I 
fitted some corona rings. What seems to happen when you try to 
put a lot of power into a small antenna is that corona discharges 
take place at the ends of the wire and at sharp bends where 
insulators are attached, where the radius of curvature of the 
conductor is small, and the potential gradient large. The heat 
generated either melts, cracks or sets fire to the insulators.

So I have fitted the corona rings, which are just hoops of stiff wire 
about 100mm in diameter, to the "hot" ends of the 3 insulators (2 
plastic and 1 ceramic) on my antenna wire. This has eliminated any 
detectable discharges from the wire, even when operating at full 
power in heavy rain. The rings are electrically connected to the 
wire. The "cold" ends of the insulators are supported with non-
conducting rope in my system, but with wire halyards you would 
want a corona ring on both ends of the insulator. It is a simple mod 
to make, and has made all the difference to my antenna, so might 
be worth a try if you are having problems.

Cheers, Jim Moritz
73 de M0BMU