On Fri, 23 Dec 2005 16:10:01 -0800, Roy Lewallen
wrote:

dansawyeror wrote:
The program zl_zin calculates a Zload from a known Zin. It would seem
that given a symmetrical feedline that Zin and Zload should be mirrors.
Why is that not so?

I'm not sure what you mean by "mirrors". But the relationship between
Zin and Zload is dictated by the way transmission lines transform
impedances. A better question is, why should it be anything else?

Roy, I also wasn't quite sure of the concept of *symmetry* and
*mirror* as used by Dan.

I made the assumption (perhaps incorrectly) that the transformation is
symmetrical for an integral number of half waves of lossless
transmission line. Impedances might be seen to "mirror" (if mirror
means an exact copy) for an integral number of half waves of lossless
line.

Having made that assumption, loss introduces errors to the
"mirroring", and line lengths other than an integral number of quarter
waves aren't symmetrical in that sense.

Having read Dan's further comments, it seems he thought any length of
real line was symmetric as an impedance transformer. It might be that
you can swap A and B ends in a circuit and obtain the same behaviour,
but you can't swap Zload and Zin in the general case.

Dan, the terms you have used don't have common usage in this context,
and confuse the issue.

Owen
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