On 11/14/2010 1:10 PM, Steve Hunt wrote:
> 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.
Yet if the common mode voltage is enough it conceivable could saturate
the core.
>
> 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.
Some but not all.
>
> 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
>
73, Jerry, K0CQ
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