>-- Tomm Aldridge <KD7QAE@ARRL.NET> wrote:
>Why are plate chokes seemingly black magic? Don't you just want a >good
>decoupling of the PS from the Plate; i.e. lots of impedance from >DC to Light
>and no resonances? How I get that should not be an issue >but all teh plate
>chokes I see are long skinny and sometimes segmented >single layer solenoids
>of questionable wire size. Why wouldn't a >really lossy powdered metal toroid
>with a few fat turns on it work, >assuming the inductance was high enough?
>
>KD7QAE
amps@contesting.com
Hi Todd,
No magic involved.
A compromise was reached long ago that most ham amplifiers have employed ever
since. By allowing the plate choke to carry some reactive current at its
lowest frequency of operation, the value may be reduced such that only a single
series resonance occurs within the 3-30 MHz region, which may then be
conveniently placed at a "safe" frequency.
The long form factor provides the best L/C(stray) ratio.
This topic is well covered in: "R.F. Chokes for High Power Parallel Feed",
by Vernon Chambers, QST, May 1954, pp30-33.
A toroid would not be the best choice for a ferrite loaded plate choke due to
the large DC component which would tend to saturate a closed magnetic circuit.
A reference on this approach is: "A Unique RF Plate Choke", by Bill Deane,
73, Sept. 1969 p. 147.
73 & Good afternoon,
Marv WC6W
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