[HomeBrew] Plate Choke

[N2EY at aol.com]

In a message dated 5/18/07 10:13:05 AM Eastern Daylight Time, 
km1h at jeremy.mv.com writes:


> Nothing wrong with the math but I doubt the tuned circuit part. 

Why do you doubt the tuned circuit part?

A multiband choke is not a straight line reactance from 1.8-30 mHz. It varies 

> considerably and some designs come very close to ham band edges yet they 
> are no more rugged in construction than the best ones. All seem to rely on a 
> bypass of .01 to .001pf depending on bands covered.

The question was about the use of relatively low-inductance RF chokes in 
applications like the Heath SB-200/201 amplifier.

In that 80-10 meter amp, they used a 50 uH plate choke, rather than the big 
millihenry-or-more chokes usually seen. Such a choke will tend to become part 
of the output tuned circuit, whether it's a pi-net or a tank with link. The 50 
uH choke Heath used probably has no unwanted self-resonances in the ham bands, 
high Q, and high current capability - characteristics that would be tougher 
to get with a millihenry-or-more choke.

All I'm saying is that Heath and others simply allowed for the reactive 
effect of the plate choke, and compensated for it in the pi-net design. 

If the choke has different reactances at different frequencies, all that 
needs to happen is to figure out the actual reactance on each band.

> 
> If I get time I'll try to research the development of the pi network. 
> Probably something in the Collins "Fundamentals of SSB" if I can find mine.
> 

Collins was a big proponent of the pi-net, even before WW2. In fact, it was 
sometimes called a "Collins coupler".

Look in any ARRL Handbook of '50s/60s and you'll see formulas and charts that 
give the values for pi and pi-L networks in terms of reactances. (that way, 
the basic solution is independent of the frequency). 

73 de Jim, N2EY


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