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
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