I guess a funny about all this is that Marconi's (and Racal and STC and
doubtless others) were making shunt fed pi networks for 30 and 50KW covering
2 - 27MHz continuously 40 years ago without any problem with RF choke
resonances. What did they know (or do) that we don't?
My father in law was an operator at some of the big HF comms stations in the
early 1950's: he tells me they didn't switch RF Chokes in the PA's, and they
didn't have problems.
One Marconi tx used (at 1KW out) a 1 inch diameter fibreglass form wound
with #24 enamelled for about a 3 inch close wound coil; then a 680pf to
ground, then ( at right angles) a bank wound coil on some more 1 inch
diameter fibreglass tube, I'd guess about 500 micro henries, and then a 0.01
mFd to ground. 1.6 to 22 MHz continuous, and it works at 24 and 28 (although
the efficiency goes because the tank coil doesn't get small enough.
73
Peter G3RZP
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