These comments are in support of considering that both series and parallel
resonances in a plate RF choke can be problematic (there is more than one of
each if you sweep on up in frequency!).
When you consider that frequencies other than the fundamental may be
significantly involved (especially in a high power stage), you can realize
that the various stray resonances of an RF choke can cause a variety of
Unexpected choke resonances can support self-oscillation, or at least allow
unplanned for voltages or currents to develop in or on the choke when
excited by strong harmonic content. They might cause a harmonic to take on
a level far above what it would have normally. E.g. A choke with a 60 MHz
self-resonance can be strongly excited by the fourth harmonic of a 15 MHz
operating frequency. That harmonic can thus be much stronger in the output
than the third or fifth harmonics.
I've seen many an HF RF plate choke die horribly or cause tough problems in
commercial HF equipment (admittedly, the power being rather higher than
levels in the Amateur service, the problems may be more dramatic).
Some manufacturers of high powered, multi-band commercial HF transmitters
dodge the bullet by switching in different chokes for different frequency
ranges. Covering 160 M - 10 M with a single choke is a very tough
challenge. The range covered by commercial HF transmitters is usually not
quite that wide, but the problems experienced are similar.
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