Am 24.11.2018 20:49, schrieb N1BUG:
So what if I could make a dummy load with the same R as that of my
antenna / earth and do the test again?
Hmmmmm, this should not be necessary when the xfmr stays cool in any way.
Could it be a defective isolator which becomes conducting after some
time. If you say the the phase is moving to leading voltage, i.e.
inductive, then something seems to reduce the capacity or is switched in
parallel to it. Maybe something becomes conducting and detunes the
antenna, still having a high voltage so that power can be dissipated and
keep the fault?
BUT... I found ONE thing that gets warm. It is that bottom-most turn
on the loading coil. The one that is a shorted turn because of the
way the tap is connected. I do not dare put my hand in there when
the transmitter is running! It takes me about 45 seconds after
shutting down the transmittter to make SURE the TX is disabled, go
outside and feel the coil. At that point, with air temperature being
about 0C today, that bottom turn (or two) is still noticeably warm.
The rest of the coil feels cold.
I have just brought the big coil inside for inspection and a
modification to eliminate the shorted turn at the bottom.
Oh yes, of course avoid shorted turns. If i remember correctly, a
shorted turn will reduce the inductivity (more than just leaving the
complete turn out of the coil). And then, if it gets hot, the induced
current will drop, so the inductivity becomes larger again.
So maybe you found it and will be on air tonite, right? ;-)
73, Stefan
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