Richard Harrison wrote:
Roy Lewallen, W7EL wrote:
"As any text can tell you, the value of Z (ratio of V to I) varies along
a line which has a reflected waves (i.e., has a standing wave)."

Not exactly, maybe the apparent Z. Uniform line is assumed and it has a
Zo determined only by line structure. Zo is identical for a signal
traveling in either direction. However, a directional coupler must be
used to measure voltage and current traveling in one direction while
ignoring voltage and current traveling in the opposite direction. A Bird
wattmeter uses a directional coupler.

I stand by my statement that Z (the ratio of V to I) varies along a line
which has reflected waves.

Voltage to current ratio on a line with reflections and standing waves
is of little practical value except for determinimg whether the capacity
of the line is exceeded or nearly so.

It's of essential use in the design of stub matching, impedance
transformation, and a host of other transmission line applications. A
Smith chart is a tool which shows this impedance, so the impedance
(voltage to current ratio) is of practical value in any application for
which the Smith chart is used.

. . .

Roy Lewallen, W7EL