[TenTec] 4229 Tuner Balun Replacement?

[Steve Hunt]

Jerry,

I must challenge you again on that statement - it simply isn't true of a 
1:1 Current Balun at the output of a tuner.

The core flux of that Balun - and therefore its loss - is determined by 
the CM signal, not the Differential Mode signal. A load of several 
thousand Ohms will simply cause a very high DIFFERENTIAL voltage 
**across the TL**, it wont of itself cause high core flux. As long as 
the TL can withstand the voltage there's no problem, and typically a 
balun for that application is wound with a bifilar pair using teflon 
insulation.

The same is not true of the commonly-used  4:1 Ruthroff Balun - there 
the load voltage appears directly across the balun as CM voltage. It's 
pleasing to see that some of the more enlightened tuner manufacturers 
are now fitting 1:1 Current Baluns rather than 4:1 Ruthroff Baluns.

Finally, in the tuner application, any change in load impedance caused 
by the short  length of TL on the core is simply "taken care of" by the 
tuner.

73,
Steve G3TXQ

On 14/11/2010 18:52, Dr. Gerald N. Johnson wrote:
> The problems with a balun on the antenna side of a tuner is that its not
> always seeing a 200 ohm load, sometimes its over 1000 ohms, sometimes
> its under 5 ohms and those often run the balun beyond its high power
> rating from high voltage with the high impedance load that increases
> core losses or high current with the low impedance load that increases
> conductor losses to the smoke point. And at the frequency range limits,
> the balun contributes considerable reactance in parallel with the
> transmission line.
>