Cecil Moore wrote in news:avVKh.3753$Qw.1263
@newssvr29.news.prodigy.net:

One fact to note is that the virtual impedance changes
all up and down a transmission line yet no additional
reflections occur while the Z0 is constant. Reflections
occur only at *actual* impedance discontinuities, e.g. at
a junction of two different Z0s.

Cecil, that is a simple statement of a scenario in which reflections
*may* occur, but *not always* occur.

Think about it and you will think of examples where a reflection does not
occur at the "junction of two Zos".

I am not quite sure what you mean by an "impedance discontinuity" beyond
the simple "junction of two different Zos" case.

The magnitude of a reflection (zero or otherwise) is *always* and *only*
related to whether the ratio of V to I for the "thing" (whether it is
another line, a lumped circuit or some combination) attached to the end
of the line is equal to Zo. The magnitude is calculated from V/I (Zl) and
Zo using a well known expression.

Should your "rule" be more correctly stated as Reflections
may occur only at *actual* impedance discontinuities, e.g. at a junction
of two different Z0s. Since it has "may" in there, it isn't a rule, is it
worth stating? It is just one of those "may"s that people like to parrot
until they become a Rule of Thumb (ROT).

Owen