Dick Rollema said
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Starting transmitting the aerial ammeter swayed wildly and I heard a
disturbing noise outside. It appeared that one half of the aerial had come
down.
It turned out that one hoisting rope had been burned through where it had
passed the pulley. Between the pulley and the "pyrex" insulator had been
some 15cm of rope. But it had been raining for several days and the rope
bust have been soaking wet. See the attachments; the top end of the rope was
on the pulley
I intend to replace the rope and to insert extra ceramic insulators of the
dog bone type as I have supplied to several British amateurs (they come from
the closed down "Radio Kootwijk" commercial PTT-station).
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I have had this trouble even when using Dick's "Radio Kootwijk" insulators.
It only seems to happen where there is a short length of insulated rope
between the insulator and the support. What seems to happen is that the
insulator eventually becomes dirty (in my case covered with a thin film of
salt). This, together with wet weather conditions, produces a conduction
path that can carbonise the short rope support. The fix is to use copper
wire between the insulator and the support fixing point.
After a storm at sea I have seen blue spark tracts running along the salt
coated insulator but this arrangement has not failed. However the insulator
should be cleaned because such sparking causes minor damage to the surface
of the insulator.
The problem reported by Dick doesn't seem to happen where there is a long
rope from the insulator to the support structure.
Peter, G3LDO
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