Am 18.01.2017 00:53, schrieb DK7FC:
BTW the antenna suddenly dropped. I had the badest thoughts, and still
have. It dropped to about 200 mA arround 22:40 UTC.
The resonance dropped a bit and the Q was much lower then. A visual
inspection showed no sign of a flashover. The PA works well and the
system is now prepared for the next EbNaut transmission on 5170 Hz
tomorrow, as usual.
Oh and my tree is back and will monitor that transmission!
I'll continue to check for a fault on the coil now...
I measured the DC resistance, normal. I applied 700 mA DC, no
inhomogenious upheating.
Why did the resonance frequency drop and why did the Q drop?
My latest thought is that it was a heavy partial discharge that started
on a developing icicle!? Maybe there was an ice layer somewhere on high
potential. Small discharges (corona/arcing...) could have forced the ice
layer to melt. This could have formed an icicle which made the
discharges stronger at a certain moment. The voltage has been 24.5 kV,
not trivial at this frequency. So maybe there is no fault. The discharge
would explain the lower resonance frequency and the lower Q. With a
partly short cut coil winding, the resonance frequency should have been
higher.
I should have tested to rise the current slowly from 0 to 600 mA and
observe the current during that time. Maybe it would have hold 500 mA
before the discharge happened. But it was late in the night and i wanted
to stop transmitting anayway. So its something to test in the next days...
73, Stefan
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