Well, I haven't used 31 mix material for common-mode chokes or current
baluns, because I didn't have any - but it would be my choice. I used
higher
frequency material because I had plenty of it - some in substantial sizes
31 isn't a magic cure-all, just as no other single material is. One of the
most difficult things in the world is designing something that fits systems
with conflicting goals.
When power levels increase, or when systems have very high voltages
impressed across the choke, a higher Q material often works better. Tuner
baluns are an example where theoretically optimum common mode impedance is
traded off for reducing heat. If a balun melts down, it is useless.
The balun that never gets hot is a short circuit or perfect lossless
reactance. The balun that has immunity to resonance is a balun that will
melt down with certain load impedances.
The ARRL still doesn't have the issue of baluns on the inputs of tuners
correct, so we have a long way to go in public education. There was a
discussion on the Elecraft reflector where someone just got it wrong in an
analysis, and an ARRL staffer used the flawed design analysis to justify a
Handbook tuner with poor balance design.
Every system has to be looked at as a system.
73 Tom
All good topband ops know how to put up a beverage at night.
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Topband Reflector
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