Peter O. Brackett wrote:

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 :-)





How are you, Peter? Is this some kind of religious controversy? I can't
imagine hams having any use for twisted pair transmission lines, but
maybe you can give your lines some fractal qualities, or show how
current can flow four directions at the same time in the same place in
them or the voltage at any given point on one of them must have 25
possible values simultaneously, or that the impedance on a typical line
is proportional to the square root of Cecil's forearm. In fact, giving
them any qualities that are impossible will endear them to
the great post hog on this newsgroup and start a never ending thread.
73,
Tom Donaly, KA6RUH

On Sun, 09 Apr 2006 21:09:07 GMT, "Tom Donaly"
wrote:

Peter O. Brackett wrote:

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.

Aren't you supposed to normalize the chart to Zo? Nothing Mr. Smith
said required Zo to be resistive.

On Sun, 09 Apr 2006 16:35:30 -0700, Wes Stewart
wrote:

On Sun, 09 Apr 2006 21:09:07 GMT, "Tom Donaly"
wrote:

Peter O. Brackett wrote:

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.

Aren't you supposed to normalize the chart to Zo? Nothing Mr. Smith
said required Zo to be resistive.


But most of the charts don't scale the area where the magnitude of the
reflection coefficient is greater than 1.

Owen
--

On Sun, 09 Apr 2006 23:42:56 GMT, Owen Duffy wrote:

On Sun, 09 Apr 2006 16:35:30 -0700, Wes Stewart
wrote:

On Sun, 09 Apr 2006 21:09:07 GMT, "Tom Donaly"
wrote:

Peter O. Brackett wrote:

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.

Aren't you supposed to normalize the chart to Zo? Nothing Mr. Smith
said required Zo to be resistive.


But most of the charts don't scale the area where the magnitude of the
reflection coefficient is greater than 1.

Most don't, but some do. [g]