Dave wrote:
"Keith Dysart" wrote in message
...

Can you kindly articulate the rules you use to know
when it is appropriate to use P = V * I?

it is extremely simple. use traveling waves then V*I works everywhere all
the time. use standing waves and it fails. period, end of story.

It does not fail. Present any example of a transmission line terminated
with a load. Choose any line and load impedance and any transmission
line length. I'll tell you the V and I at any point on the line,
calculate the instantaneous power from V(t) * I(t) at that point, and
from that the average power. Then I'll show that this average power
equals the power in the load and the power delivered by the source. As
an added bonus, I can tell you the impedance (ratio of V/I) at any point
along the line. I'll provide both equations that always work and
numerical results.

Then you can show where I've made an error and why my calculations are
invalid.

Can I be any more fair than that?

Roy Lewallen, W7EL