wrote:
When excited by a sinusoid, no energy moves at the quarter wave points
where the voltage or current is always 0.

You keep saying that and it keeps being a false statement. There is
absolutely nothing magic about sinusoids.

"we know" is rather strong. I would strongly suggest that no energy
crosses those points in the line where the voltage and current are
always zero since p(t) is always zero at these points.

What about Ramo and Whinnery's forward Poynting vector and reflected
Poynting vector? Why do you choose to ignore them?

Not necessarily. Only once the line has been charged, does the energy
move back and forth between the quarter wave points, while not
crossing them.

That has been shown to be a false assertion regarding component waves.
There is no impedance discontinuity to cause any reflections. Therefore,
the waves do not move back and forth. Do you really believe that the
energy in a bright interference ring is trapped inside the ring? Get
serious!
--
73, Cecil http://www.qsl.net/w5dxp



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W5DXP wrote:

wrote:
When excited by a sinusoid, no energy moves at the quarter wave points
where the voltage or current is always 0.

You keep saying that and it keeps being a false statement. There is
absolutely nothing magic about sinusoids.

Seems to me that the sinusoidal standing wave with minima and maxima
at the quarter wave points can only arise with single frequency
sinusoidal excitation of the line. Are there other signals which
will produce this result?

"we know" is rather strong. I would strongly suggest that no energy
crosses those points in the line where the voltage and current are
always zero since p(t) is always zero at these points.

What about Ramo and Whinnery's forward Poynting vector and reflected
Poynting vector? Why do you choose to ignore them?

I haven't used them because I don't need them to arrive at an answer.
Basic electricity, a dash of circuit theory, a bit of knowledge of
trigonometry, some basic calculus and the ability to think is all
that is required.

Why make the solution more complex than necessary?
Just to scare off the neophyte?

Not necessarily. Only once the line has been charged, does the energy
move back and forth between the quarter wave points, while not
crossing them.

That has been shown to be a false assertion regarding component waves.

Perhaps. Or maybe component waves are not the answer.

There is no impedance discontinuity to cause any reflections. Therefore,
the waves do not move back and forth.
Do you really believe that the
energy in a bright interference ring is trapped inside the ring? Get
serious!

In this context, we are discussing transmission lines. I make NO
assertions about light, how rings happen, or don't, or whether the
theory and practice of optics is in way analogous to what happens
on a transmission line.

Transmission lines and their understanding can stand on their own
without the help of optics.

....Keith

wrote:
Seems to me that the sinusoidal standing wave with minima and maxima
at the quarter wave points can only arise with single frequency
sinusoidal excitation of the line. Are there other signals which
will produce this result?

Probably not, but that makes sinusoids unique, not magic.

What about Ramo and Whinnery's forward Poynting vector and reflected
Poynting vector? Why do you choose to ignore them?

I haven't used them because I don't need them to arrive at an answer.

You need them to keep from making the same mistakes over and over.

Why make the solution more complex than necessary?
Just to scare off the neophyte?

Nope, your solution is simple-minded.

Perhaps. Or maybe component waves are not the answer.

Then go argue with Ramo & Whinnery.

In this context, we are discussing transmission lines. I make NO
assertions about light, how rings happen, or don't, or whether the
theory and practice of optics is in way analogous to what happens
on a transmission line.

You will never understand the present topic unless you understand that
EM wave interference doesn't affect the flow of energy in the individual
waves. That is true for light and RF.
--
73, Cecil http://www.qsl.net/w5dxp



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W5DXP wrote:
You will never understand the present topic unless you understand that
EM wave interference doesn't affect the flow of energy in the individual
waves. That is true for light and RF.

I should have added: "in the absence of a physical impedance discontinuity."
If a physical impedance discontinuity exists, then of course, the flow of
energy in the individual waves is affected by reflections.
--
73, Cecil http://www.qsl.net/w5dxp



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W5DXP wrote:

wrote:
Seems to me that the sinusoidal standing wave with minima and maxima
at the quarter wave points can only arise with single frequency
sinusoidal excitation of the line. Are there other signals which
will produce this result?

Probably not, but that makes sinusoids unique, not magic.

Magic was your moniker not mine. But I am glad that you agree.

What about Ramo and Whinnery's forward Poynting vector and reflected
Poynting vector? Why do you choose to ignore them?

I haven't used them because I don't need them to arrive at an answer.

You need them to keep from making the same mistakes over and over.

I've being using p(t) = v(t) * i(t) and simply arguing that when
v(t) or i(t) is zero for all t, then there is no power.

Poynting won't change a thing. There is no P when E or H is zero.

So the debate can be had with the simpler p(t) = v(t) * i(t).
There is no need to complexify.

....Keith

wrote:
Poynting won't change a thing. There is no P when E or H is zero.

Of course, there are the two component Poynting vectors which each
contain power. How else could (Pz-/Pz+) = |rho|^2

You are continuing to confuse NET power with component power. The
NET Poynting vector is zero. The component Poynting vectors are
Pz- and Pz+ and NOT zero as explained in Ramo & Whinnery. The sum
of the two Poynting vectors is zero at certain points because they
are 180 degrees out of phase at those points. 1/4WL away, they are
in phase.
--
73, Cecil http://www.qsl.net/w5dxp



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wrote:
What about Ramo and Whinnery's forward Poynting vector and reflected
Poynting vector? Why do you choose to ignore them?

I haven't used them because I don't need them to arrive at an answer.

Yes, but you need them to arrive at the correct answer. :-)

Basic electricity, a dash of circuit theory, a bit of knowledge of
trigonometry, some basic calculus and the ability to think is all
that is required.

Apparently, that is not all that is required. Here's a neat web page
that will allow you to visualize what is happening. Note the forward
and reflected waves do not change energy or momentum at a zero
voltage point.

http://www.gmi.edu/~drussell/Demos/s....html#standing
--
73, Cecil http://www.qsl.net/w5dxp



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Keith wrote:
"Basic electricity, a dash of circuit theory, a bit of knowledge of
trigonometry, some basic calculus, and the ability to think is all that
is required."

An electrical education limited to d-c familiarity leads to mistaken
assumptions when dealing with a-c in Keith`s case it seems.

Best regards, Richard Harrison, KB5WZI