On 10 jun, 01:45, lu6etj wrote:
On 9 jun, 23:55, 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.

These two simulations do not claim to show energy moving all the
way down the line in both directions, nor do they superpose powers.
So they look fine.

...Keith- Ocultar texto de la cita -

- Mostrar texto de la cita -- Ocultar texto de la cita -

- Mostrar texto de la cita -

Hello Keith:

I believe I just understand where is the problem *You are talking
about "Superposition Theorem" of circuit theory and we are talking
about "Superposition pinciple of waves". There are not the same stuff.
Please read this page from "Physics for scientists and engineers with
modern physics" book to aliviate my translation :)

http://books.google.com.ar/books?id=...01&lpg=PA501&d...

Uf, what a large link!! If do not works search on page 501 of Google
books with the appointed title.

Note = "Two travelling waves can pass trough each other without being
destroyed or even altered". (Op. Cit.). (Please pay attention to pond
example).

The applet there do not represent an opticall illusion, You can
experiment with different shape opposite end launched pulses in a rope
to verify that do not collide but pass through each other. It is a
usual student laboratory work on applied physics.

73

Miguel ghezzi LU6ETJ

PS: Yes Richard I live outside of Buenos Aires city. I hope you have
been welcome on your visit to Argentine... and... what do you think of
our beautiful girls, ah? ;D- Ocultar texto de la cita -

- Mostrar texto de la cita -

Before I forget... Here is early mornig and I am ready for bed (I'm
nocturnal habits). I want give a QSL to Cecil's comment on Maxwell
article and Joe's example in CC. Also, noblesse oblige, I recall that
Cecil make this comment in a very early post in this thread:

Yes, standing waves are hard to visualize, but there is indeed
same- cycle interference involving forward waves and reflected
waves. There is a certain delay from the source signal to the
load and back that can be calculated if one chooses. The
wave reflection model is closer to Maxwell's equations than
is the lumped-circuit model where EM waves propagate
instantaneously.

Pointing to differences between lumped constants circuit theory models
(superposition theorem) and TL issues. I aknowledge his linked page
=
http://www.google.com/url?sa=D&q=htt...06V-3Vix1MXnrA
where it said:

"There are no standing waves on a lumped element circuit component.
(In fact, lumped-element circuit theory inherently employs the
cosmological presupposition that the speed of light is infinite, as
every EE sophomore should know. See, e.g., - Electric Circuits, by
J.W. Nilsson, Addison-Wesley, 1983, p. 3.)"

Probabily Cecil had in mind this controversy when I submitted my
question to this newsgroup. He will correct me if I am wrong.

Thank you very much, and now, I am go to ZZZZZZZ...!

Miguel