On Monday I had a visit from Laurence, KL1X. He was on his way from Surrey
to Exeter and by the time he got here it was dusk. I showed him the garden
shed transmitter shack and fired up the transmitter. I explained that the
antenna current was behaving strangely lately, starting off rather low then
building up. Laurence noticed that, in the half light, there was sparking
occurring, in several places, inside the plastic covering of the 4mm Litz
wire coil windings. We concluded that there must be damp inside the litz
wire that had to be 'cooked' out before full power could be achieved.
Building up a head of steam so to speak!
Laurence remarked that he was aware of the problem in commercial LF set-ups
and that this had been cured by arranging loading coils to be surrounded by
an atmosphere of dry air. The Decca loading coil buildings had extensive
electrical heating as I recall.
Over the last few days I have cooked the loading coil by placing against
radiator in the house. In the last couple of days the weather has become dry
with a cold drying northerly wind.
This morning, before taking the antenna down, I fired up the transmitter and
the current meter hit 9.2Amps! The Decca transmitter 6amp current meter was
endstop. I quickly switched off and tried different taps on the matching
transformer. The antenna system seems to have a total resistance of about 20
or 25ohms at the moment and the tuning is very twitchy - the slightest
movement of the antenna in the wind causes large variations of antenna
current.
I am not sure what is going on. I can only conclude that it is a combination
of a dry loading coil and dry weather condition and a high tide. I had also
cut down a lot of Ivy that covered a near dead tree about 3m from the
loading coil.
Or it might be the KL1X effect!

Regards,
Peter, G3LDO

e-mail <[email protected]>

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