Roy, W7EL wrote:
"A Bruene wattmeter circuit measures "forward power" and "reverse power"
just fine simply by measuring the voltage at a single point on the
line."

So does the Bird Thruline Wattmeter., and it has been doing so for about
half a century.

It uses the fact that reflection reverses the phase between voltage and
current on a 50-ohm coaxial line. That means forward waves can be
separated from reflected (reverse) waves. Bird designs its measuring
elements to extract a line voltage sample that causes the exact same
meter deflection as does a line current sample.

From a wave traveling in one direction the samples add. From the wave
traveling in the opposite direction, the samples exactly cancel in the
meter. Voila! a directional coupler.

It was A14QJ who wrote:
"The components of the superposition wave no longer exist by
themselves;----".

My reply was:
"The components are not cancelled. Were that so, the Bird Thruline
Wattmeter could not function and the standing wave would be independent
of the forward and reflected waves. Instead it is only a manifestation
of interference."

I don`t have a Bruene wattmeter, but I believe it functions like a Bird
but uses transformers to couple to the transmission line.

Best regards, Richard Harrison, KB5WZI