K7ITM wrote:

Which, of course, illustrates the point that I believe Roy made in the
article, that the load conditions (whether they are the result of
something going on involving a transmission line, or just a lumped
load) tell us nothing about what's going on inside a source, ideal or
otherwise. For that, you MUST know the characteristics of the source
itself, and for that you do NOT need to know anything about the load
beyond the impedance it presents to the generator output terminals
(possibly as a function of time, frequency, amplitude and other
factors). For example, in the case of the signal generator on my
bench when 100dB of attenuation is cranked in, the change in
dissipation inside the generator versus load impedance is
inconsequential: at least 99.999 percent of the generator's available
RF output is dissipated in the attenuator when the load is matched (50
ohms). The additional maximum possible 0.001 percent increase
depending on load would be difficult to detect: about 0.00004dB
change. On the other hand, the change in dissipation inside my 450MHz
transmitter versus load impedance is substantial, BUT bears no
resemblance to either the current-source-with-shunt-resistor or the
voltage-source-with-series-resistor model, for multiple reasons.

Yes. In all the cases, you can replace the transmission line and load
with any other combination of transmission line and load which present
the same impedance to the source, and the source resistor dissipation
will be exactly the same.

For example, look at the first entry, 50 + j0:

Zl fPa rPa Pa(tx) Pa(src) Pa(R0) Pa(Rl) frac R0 frac Rl
50 + j0 100 0 100 200 100 100 0.50 0.50

If we used a 100 ohm transmission line instead of a 50 ohm transmission
line, we'd have

Zl fPa rPa Pa(tx) Pa(src) Pa(R0) Pa(Rl) frac R0 frac Rl
50 + j0 112.5 12.5 100 200 100 100 0.50 0.50

There's no change in source or load dissipation even though the forward
and reverse powers in the transmission line are different. If we do away
with the transmission line altogether and connect the load directly to
the source resistor, completely eliminating traveling waves, the result
is exactly the same.

A literally infinite number of other examples, using various line
impedances, load resistances, and line lengths, can be created. You'll
find that the *only* factor (other than source voltage and source
resistance value) which determines source resistor dissipation is the
impedance which it sees - regardless of how that impedance is created.
It has nothing to do with constructive or destructive interference,
traveling waves of voltage, current, or power, or anything else
happening on the line, or even if there is a line at all. And the exact
amount of source resistor dissipation can be immediately calculated by
analyzing a simple circuit of three components: the voltage source, the
source resistance, and the impedance seen by the source resistance. No
other information is required.

Roy Lewallen, W7EL