> Case in point: High Voltage RF Chokes that calculate
> one way, measure another way on the bench and then
> let the white smoke out when they're installed in the
> amp's
> RF Chamber with all the covers on.
That's because the choke, at the lowest order series
resonant point, acts like two back-to-back L networks with
very high L and low C. Since the impedance step up and step
down closely match, the throughput impedance of the choke
drops to very low values. Only resistive losses remain.
When you install the choke in a PA everything within several
inches of the choke changes the shunting capacitance of the
L networks, and the frequency moves around a good bit.
They have to be measured in place with all the major metal
objects around the in place.
At higher order series resonances it can look like any
number of L network pairs back-to-back in series.
Removing turns at the voltage maxima points (highest E
field) has the largest effect on series resonant
frequencies. So if you have a resonance parked in a Ham band
just slide a metal screwdriver blade along the choke until
you see the resonance shift the largest amount possible, and
take turns off in that spot.
73 Tom
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