> A balun work's best when it see's a pure resistance, or nearly so. A
> balun at the end of a piece of coax, feeding a length of balanced line
> that feeds an antenna, will almost be guaranteed to see a reactive load.
A choke balun cares less if the load is reactive, only voltage baluns
(like the W2FMI style) are load impedance critical.
> A better idea would be to place the balun at the input of a balanced
> tuner. If there are difficulties in bringing in the balanced line to the
> tuner, then a small section of shielded balanced line can be employed.
Placing a choke balun at the input of a tuner does nothing for
balancing of the system, although it does reduce differential mode
stress on the balun (which usually isn't a problem anyway if you
use a properly constructed choke balun).
After some discussion of this in another antenna forum, Roy
Lewallen (W7EL) did an analysis and confirmed this.
73, Tom W8JI
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