[Elecraft] [BL1] Seems lossy in all useful configurations

[N2EY at aol.com]

In a message dated 10/13/07 4:58:04 PM Eastern Daylight Time, vic at rakefet.com 
writes:


> There is no difference if the balun is on the input or output side of an 
> unbalanced tuner.

In theory, no.

In practice, there can be a big difference.

 See
> 
> 
> <
> http://fermi.la.asu.edu/w9cf/articles/balun/balun.html#SECTION00050000000000000000> 
> 

He's not looking at the big picture.

If the balun is ideal, or close enough to ideal, or if the shack-end 
impedance of the balanced load are within a certain range, the 
unbalanced-tuner-with-balun-at-the-antenna-end idea works fine.  Thousands of hams use it with no 
problems and good results.

But in some cases the shack-end impedance of the balanced line can be very 
high, very low, and/or highly reactive. Under those conditions some baluns don't 
work well, and all sorts of odd things happen. Sometimes the end result works 
well enough that the ham doesn't notice anything wrong, particularly if s/he 
has nothing else for comparison.

Sometimes the problems can be fixed by things like changes to the line length 
or adding reactive elements in parallel or series with the line. 

You can't just blindly increase the number of turns on a wound-core balun to 
increase the impedance because you may set up self-resonances that cause all 
kinds of fun.

The best approach IMHO is to model the antenna-feedline system and see what 
the actual shack-end impedances are. Or measure them. Then decide what tuner 
setup is needed to do the matching job.

73 de Jim, N2EY


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