Gamma Fans:

One area of practical interest for which Zo is not "real" occurs over
[broad] ranges is in the area of application of the so-called "last mile"
[for you Newbies that might be "first mile" (grin)] of POTS (Plain Old
Telephone Service) twisted pair transmission lines to a variety of
communications "last mile" communications systems.

Over the frequency ranges of interest for telephone cable applications i.e.
from below 25Hz or so for some signalling and on up to several hundred kHz
or even a few MHz for xDSL applications such as ISDN BA and HDSL, T1,
etc..., the telephone twisted pair exhibits a Zo that varies all over the
map!

In this arena, complex Zo and highly variable Gamma is the norm, in this
twisted pair media and for those kinds of applications, unfortunately for
Mr. Smith Zo is NOT purely resistive.

The Zo of twisted pair ranges rom very nearly purely capacitive impedance of
several thousand kOhms at low frequencies to purely resistive near 100 Ohms
at the higher ends.

Analysis and design of systems that operate over this 5-6 decade range of
frequencies must perforce use complex Zo!

Smith's venerable chart is completely useless. Smith's Chart is only for
"amateurs" who use transmission lines in very limited ways.

The complex reflection coeficient in all of its' glory reigns supreme for
those practical and realistic design and application scenarios.

Thoughts, comments?

--
Pete k1po
Indialantic, FL.


"Wes Stewart" wrote in message
...
On Sat, 08 Apr 2006 01:34:33 GMT, Cecil Moore
wrote:

Reg Edwards wrote:
But, believe it or not, under certain load conditions the reflection
coefficient Gamma can exceed unity. Indeed, at a sufficiently low
frequency, Gamma can approach 1+Sqrt(2) = 2.414

That agrees with Chipman who says it only occurs in lossy lines.

But in theory, the line can have loss and this does not occur :-)