G3NYK wrote:
Hi Mike, and all, could it be that the insulators are good.....I cannot
really see Decca (or Racal ) using rubbish in the PAs...... Might it be
that
Perspex will burn if there is an ignition source. In this case the
ignition
source is the 'sharp' end of the wire, which is subject to corona
discharge
(mini plamsa torch) when excited.
I don't think it was corona. Corona tends to be quite small and erode
slowly. What I saw was a yellow arc some 8cm long, running the length of
both insulators. This is not the normal property of a good insulator.
When used by Decca, these bits of transparent plastic are not in contact
with the Litz wire. they hold the slotted triangles that hold the wire.
Perhaps there is less need to make these good insulators. The triangles
themselves are certainly good for RF. I use one as a stand-off to prevent
the up-wire touching my mast in a high wind. They are brittle, however, and
would not be suitable when pulling strain is involved. The really good bits
from the Decca sites are definitely Perspex and are originally about 40cm
long by about 5cm and some 40mm thick with a large hole at one end. I have
chopped these into 10cm lengths for use on the antenna.
The problem that Peter had with salt on his insulators is, I understand,
also troubling the French railways after the storm.
Mike, G3XDV
http://www.lf.thersgb.net
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