K7ITM wrote:
It's easy to lose sight of what's important when you get bogged down
in numerical coincidences and the like. To me, some things are
clearly important with respect to analyzing such systems:

Is it a coincidence when one amp flows through a one ohm
resistor with one volt across it and dissipates one watt?
No, it is the laws of physics in action. The fact that
everything is a unity magnitude is because of the particular
values chosen for the example.

My example was NOT coincidence. I deliberately chose values
that would cause the forward wave and reflected wave to be
90 degrees out of phase at the source resistor. Under those
conditions, there is no interference present and all of the
reflected energy is dissipated in the source resistor. There
are an infinity of such examples and it is true for both
voltage sources and current sources.

The fact that there is even one example discredits the assertion
that reflected energy is *never* dissipated in the source.

1. If a generator is linear and matched to a line (Zgen = Zline, not
Zgen* = Zline), then no matter where a "reverse" signal comes from,
that signal does not reflect at the source:line junction. The
"reverse" signal can come from a reflection at a load, from another
generator at the other end of the line, from something feed in through
a coupler, from an electric eel biting the line--it doesn't matter.
There is no need for an analysis involving "constructive" or
"destructive" interference.

An interference analysis reveals exactly where all the energy is
going and that's what this discussion is all about. It may not
matter to you but it obviously matters to Keith and me.

1a. Just because a "reverse" signal on the line does not reflect at
the generator:line junction, that does NOT mean that additional power
is dissipated inside the source.

That's true. If total destructive interference exists at the
source resistor, then all of the reflected energy is redistributed
back toward the load. For the simple sources we have been using,
predicting how much reflected energy is dissipated in the source
resistor is a piece of cake.

I took Roy's chart and without calculating a single voltage or
current, not only matched Roy's correct results but I uncovered
an error he had made. That's a pretty good track record considering
that Roy's data went unchallenged for many years.

2. You MUST have an accurate model of the inside of the source to
know how it will respond to some particular load and to signals that
impinge on its output port. With respect to figuring out what goes on
inside the source and what power may or may not be dissipate there,
there is NO advantage to knowing how the load or signals got there.

We are discussing single-source, single transmission line, single
mismatched load systems. Where the energy components come from is
obvious.

3. To correctly analyze conditions on a line that's fed only from one
end, with a load on the other end, there is NO NEED OR ADVANTAGE to
know what goes on inside the generator (beyond knowing the power it
delivers to that effective load, perhaps).

This discussion is all about what is going on inside the source.
If you don't care to engage in that discussion, please feel free
not to.

3a. There may be some advantage in knowing the source impedance of a
generator (or transmitter) in calculating the power delivered to a
load at the source's output port, but there is no advantage to knowing
it if you want to determine the standing wave ratio or reflection
coefficient on the line, or what net impedance that line+load presents
to the source; that is all determined solely by the line and the load.

The argument about what happens inside a source is about 20 years
old now and is still raging. I'm simply trying to contribute
something to that argument.

The stuff about constructive/destructive interference with respect to
figuring out what happens inside a source is, to me, just so much
dancing on the head of pins. Welcome to dance if you so wish, but I'd
just as soon sit that one out.

That's your opinion and that's OK. If you choose not to attempt
to understand interference, you will forever remain ignorant of
its usefulness as an analysis tool. For the simple examples presented
so far, how much reflected power is dissipated in the source
resistor has been accurately predicted for all examples.

The interference phenomenon is well understood in the field of
optical physics and is a very useful tool in that field. The
principles are the same for RF waves. Why not use the tool?
Incidentally, optical physicists are NOT dancing on the head
of a pin when they calculate the irradiance of the bright rings
and dark rings.
--
73, Cecil http://www.w5dxp.com