Johnson uses the same term of "interaction" to describe the origin of
the extra power term. However, you can hopefully see from the analysis I
posted that only ordinary superposition of the forward and reverse
voltage and current waves is necessary for the term to appear. So I
don't feel that "interaction" is entirely appropriate. The extra term
actually is a result of the calculation of average power. I've said many
times that it's risky to abandon the time information in the power
waveform and deal only with averages. If the voltage and current in each
wave aren't in phase with each other, there are components of the total
VI product that add together but don't show up in the averages of the
individual forward and reverse average powers. There's no mystery or
true "interaction" involved. The "problem" lies simply in calculating
average "forward power" and "reverse power" separately, throwing away
all time related information, then expecting them to add or subtract to
get the total.

Roy Lewallen, W7EL

pez wrote:
-
"The Third Term"
-
Roy Lewallen wrote:
-
| No, the average Poynting vector points toward the load.
| Power leaves the line and enters the load, as it should.
| ...
| I imagine your problem
| with the solution is your notion that
| the total average power
| is the difference between the
| "forward power" and "reverse power".
|
| But it's not.
|
| I gave the equation showing what the total power
| is, and as you can see,
| there's a third term involved.
| When this is
| taken into consideration, you see that there's a net power flow out of
| the line into the load, as there should be.
| ...
-
As usually,
Mr. Roy Lewallen,
points the right direction.
And this time,
it is of:
-
"The Third Term".
-
In the whole of the book by R.A.Chipman,
a phrase, less than a printed line,
is proved enough to cause a major upset:
-
"The third term
on the right
represents interaction
between the two waves."
-
But when there is such a steadfast loyalty
to the existence of some kind of
"interference"
between two,
rather clearly distinct waves,
the incident and the reflected one,
it is difficult for anybody
to compromise himself and accept
that the same two waves,
so clearly distinct until now,
when are coming along a line with complex Z0,
have to bear in addition
some kind of
"interaction".
-
Very difficult, indeed.
-
Sincerely,
-
pez
SV7BAX
-