On Jun 10, 2:55*am, Keith Dysart wrote:
On Jun 9, 2:37*pm, lu6etj wrote:



On 9 jun, 13:23, Cecil Moore wrote:

On Jun 9, 8:26*am, Keith Dysart wrote:

6. Keith, using basic circuit theory, reflection coefficients and
* *analysis in the time domain, shows that Cecil's conclusions do not
* *align with expected behaviours.

I must have missed the posting where you proved RF waves do not obey
the *average* power density (irradiance) equation from "Optics", by
Hecht. Neither Hecht nor I have ever said anything about instantaneous
virtual power except that it is "of limited usefulness". Nothing you
have posted about instantaneous virtual power has disagreed or
disproved anything that I have said about *average* power where I
simply quoted Hecht. I suspect that your instantaneous virtual power
must necessarily obey the conservation of energy principle but I am
not going to waste my time trying to prove it. Hecht and I seem to
agree 100% that *average* energy flow obeys the laws of physics.

May I suggest that you read "Optics", by Hecht and post anything with
which you disagree. I, and others, stopped taking you seriously when
you said that an equal magnitude of the forward Poynting vector and
the reflected Poynting vector proves that zero energy is crossing the
boundary (without adding that it is zero NET energy). You have
probably ruined your technical reputation with such nonsense.
--
73, Cecil, w5dxp.com

Good evening. (sunny and cold day, here)

Superposition works just fine for voltage and current,

And electromagnetic waves... We also study TL in physics with a
electromagnetic model (E-H fields).

Yes, of course.

but is mostly
invalid for power. Attempting to apply superposition to power will
lead to inaccurate results.

Yes. As Cecil pointed, power not apply to superposition because it is
a scalar magnitude.

Not quite. It does not apply to power because it does apply to
voltages.
If one doubles the voltage, one gets 4 times the power. There is no
way to make superposition (which is simply addition) simultaneously
work
for voltage and power.

As for scalars... Superposition works quite fine for circuit analysis
with scalars.

I am curious as to what I wrote on the web page that suggested
disagreement with the superposition principle.

Because my interpretation of this sentences on the wave page:

What happens when the signals from two identical generators
at each end of a transmission line collide in the middle?

Term "collide" without quotes suggest (to me) interaction (as
particles). I learnt travelling waves do not "collides" in space (or
linear mediums), simply they crossing each other (as ghosts).( I do
not be sure about this translation)
or, quoting UCLA web page note, "Wave maintain their integrity upon
overlapping (without themselves being permanently changed)".

Superposition is a mathematical trick that allows the solution of
the problem. It does not mean that the pulses pass through each
other, though that is one of the visualizations. Consider a point
on the line where the current is always 0, no electrons cross
this point nor does any energy. Did the pulses cross through
such a point? The voltage envelope appears to, but does that mean
the pulse did?



Does energy cross the midpoint of the transmission line?
.....
The plot shows that the voltage in the middle of the transmission
line is always zero (that's femtoVolts on the left, not a bad
representation for 0 in a simulation). Recalling that Power =
(Volts times Amps), if the voltage is always 0, then there
is no power. With no power, no energy is crossing the
middle of the transmission line.

My interpretation of last sentence (and reading technical controversy
with Cecil and K1TT in thread) make me think that it does not match to
superposition principle (except when there are not any travelling
waves in system, of course). (I do not considered here spice
application to travelling wave model issues).

Please tell me if you agree with Java applets linked -applied to TL
travelling waves- to clarify my understanding of your proposition.

I have no issues with the applets. They show voltage waves crossing
each other and appropriately use superposition to derive the results.

Like many optical illusions, there are multiple ways to visualize
what is happening. The second one for example can also be seen as
the two pulses bouncing off of each other. The response would be
identical if the transmission line was cut at the point of collision.


only in the very special case of the far end being an open or short
circuit and the line being lossless. simulate it for a more general
case of a load other than those and see what happens.