Richard Harrison wrote:

Keith wrote:
"It does go back to "double think" unless you can explain how energy can
flow when power is zero."

Think! The only way the voltage can go to zero on a good transmission
line which is energized is by interference between an incident wave and
a reflected wave. Zero volts on the line is merely a manifestation of
VSWR.

No disagreement from me as long as you replace 'incident wave' and
'reflected wave' with the more precise 'incident voltage wave' and
'reflected voltage wave'. This aligns with the precise use of V in
VSWR.

Adopting Roy's more precise notation for power
P(t) = V(t) * I(t) (1)
The question is: Do you accept this expression as describing power?

a) If not, then there is no "double think", but a lot of electrical
engineering will have to be tossed as well.

b) If you do accept (1), then in a case where V(t) is zero for all time,
power must be zero as well. V(t) is zero for all time at a current
maximum in a shorted transmission line, so the power (energy flowing)
must be zero as well.

c) If you accept (1), but also claim that there is energy flowing when
V(t) is zero, then "double think" is an appropriate description.

I think these are the only 3 options.

If you choose b), then I think we are in agreement.
If you choose c), then ... I'm not sure what the 'then' is.
If you choose a), we can explore all the difficulties that will arise
when (1) is not true and with some effort you may arrive at b).

Forward (incident) power and reverse (reflected) power are both on the
line. A zero voltage on the line requires a complete load reflection so
that the reflection volts are as strong as the forward volts.

The sentence with 'volts' is correct. The sentence with 'power' leads
to a great deal of difficulty as described above.

A directional coupler, at the very spot where a slotted line probe would
sense zero volts, would show you have full power (with its volts and
amps) coming and going.

Many people use directional couplers as a reason to stay out of
camp b), but this necessarily means they are in a) or c). The first
step to enlightenment is to briefly set aside directional couplers
and 'Bird watt' meters, and realize that in a choice between a), b)
or c), b) is the only place it makes sense to be. Then go back and
figure out how directional couplers are not inconsistent with b).

In reality there is not zero volts in the incident wave or in the
reflected wave. There`s full voltage coming and going. The volts just
happen to be out-of-phase at this point.

Yes, indeed. But there is no power.

....Keith