I had only a few moments before finishing today, but while I had the
network analyser on, I looked at a 100pF variable such as might be used
as an anode tuning cap - semi-circular vanes about 1.5" diameter,
spacing around .1"
I measured between the rear centre bearing and one of the corner bolts
of the stator rail, frequency range 10-300MHz.
Fully meshed it looks like 110pF at 10MHz, short circuit at about
100MHz, then goes inductive to an 'open circuit' at 270MHz. Actually,
it's lossy and looks like 300 ohms or so resistive.
I added a few inches of thick wire to simulate the anode to capacitor
lead and then, looking at it from the anode's point of view, both series
and parallel resonances ('short' and 'open' circuit respectively) went
down in frequency a bit.
At half mesh, it doesn't get as far as an 'open' circuit resonance.
The loading cap out of a MLA2500 (fully meshed) goes through 3 low-Z
resonances and 2 high-Z resonances in the frequency range (2 and 1 at
half mesh).
More info. next week when I get a chance, got to go pack for a contest
now.
Cheers, Steve
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