Keith Dysart wrote:
Numerical coincidence as proof that Pref is always
dissipated in the generator. :-)

It's no coincidence. The special case example was
carefully selected to make the angle 'A' between
the forward and reflected waves equal to 90 degrees.
Since cos(A) exists in the interference term and
cos(90) = 0, it makes the interference term equal
to zero.

When there is no interference at the source resistor,
100% of the reflected power is *always* dissipated in
the source resistor. This is a chosen special case
condition, NOT a coincidence. In the absence of
interference, there is simply no other place for the
reflected energy to go, i.e. it cannot be redistributed
back toward the load.

There are any number of special cases that will cause
the forward wave and reflected wave to be 90 degrees
out of phase at the source resistor. One of Roy's cases
was just such a case - 1/2WL of 50 ohm feedline with a
0 +/- j50 ohm load.

For any length feedline, there exists a load that
will cause the reflected wave to be 90 degrees out of
phase with the forward wave at the source resistor.
For any of those infinite number of cases, the
reflected energy will be dissipated in the source
resistor.

On a more serious note, how would you analyze this
generator using reflected power and constructive
and destructive interference?

Without analyzing it, based on our previous discussion
of voltage sources and current sources, I would say
that any constructive interference in the voltage
source is offset by an equal magnitude of destructive
interference in the current source and vice versa, i.e.
the net interference inside the source is always zero.
--
73, Cecil http://www.w5dxp.com