Topband: Thanks!

[Charlie Cunningham]

Well, I've wondered about the heating of 31 material because of the large
resistive term.

I've used higher frequency material (71 as I recall) because I had lots of
it in all shapes and sizes in Designer Kits and we used it a LOT of it to
reduce high-frequency emissions from electricity meter electronics on wiring
and cables that exited the meter. Nothing really to "ground" to on a meter.
The chassis is connected to one of the line phases!! Problematic for
external antennas, too!!

Charlie, K4OTV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Tom W8JI
Sent: Tuesday, May 21, 2013 10:08 PM
To: topband at contesting.com
Subject: Re: Topband: Thanks!

> 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.
_________________
Topband Reflector