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
|