Standing-Wave Current vs Traveling-Wave Current
 

Gene, W4SZ wrote:
"Some people like to treat standing waves as poor distant cousins to
"real" waves, or perhaps as "only envelopes"."

Frederick J. Bueche & Eugene Hecht may have said it best in "Schaum`s
College Physics Outline": "Standing waves---These might better not be
called waves at all since they do not transport energy and momentum."

Best regards, Richard Harrison, KB5WZI

Standing-Wave Current vs Traveling-Wave Current
 

On Thu, 3 Jan 2008 20:53:14 -0600, (Richard
Harrison) wrote:

Gene, W4SZ wrote:
"Some people like to treat standing waves as poor distant cousins to
"real" waves, or perhaps as "only envelopes"."

Frederick J. Bueche & Eugene Hecht may have said it best in "Schaum`s
College Physics Outline": "Standing waves---These might better not be
called waves at all since they do not transport energy and momentum."

Hi Richard,

One of the bug-a-boos of definition crafting is using the term within
its own definition. Even worse, is to define in negative terms (there
are an infinite number of things that so qualify) such as a suitcase
is not a planet, not a speaker, not a window, not a.... ad nauseam.

In other words "Standing Waves" are not "Waves" is sloppy writing.
Going on, "transporting momentum?" Egads! Now there's an example of
over-the-top writing. It could only provoke a goggle-eyed question of
"how is momentum transported?" FedEx or UPS?

Does transporting energy mean accelerating a moving charge? Or moving
a static charge? Both are energy, and yet one usage is slightly more
comprehensible than the other. Does a surfer violate this definition?
Would he be classified under traveling waves? (groan)

Hecht may be a commendable spirit, but his acolytes are trashing his
legacy.

73's
Richard Clark, KB7QHC

Standing-Wave Current vs Traveling-Wave Current
 

On Jan 3, 12:55*pm, Mike Monett wrote:
* Keith Dysart wrote:

* [...]

* You did *not directly answer Q1, but I take if from all *the other
* responses that *you *are *saying *the answer *is *"no, *it *is not
* appropriate to view a transmission line as distributed capacitance
* and inductance *and analyze its behaviour using *charge *stored in
* the capacitance and moving in the inducatance?"

* That is not what you originally stated.

* Taking this *invalidates all the subsequent *questions *since they
* are based *on *the * premise * that * this * kind *of *analysis is
* appropriate.

* Yes, it does.

* Your explanation is easily proven false. Let's suppose it was true.

* Suppose it *was *possible *to introduce a *pulse *of *charge *onto a
* conductor.

* Since like charges repel each other, what keeps the pulse together?

* In other words, what prevents it from destroying itself?

* Then, when *the first pulse meets the second, what *mechanism allows
* them to bounce off each other?

* Then, after *they have bounced off each other, what *mechanism keeps
* them together?

All good questions. But it appears that your underlying
suggestion is that charge and charge flow in the distributed
capacitance and inductance can not be used to analyze
transmission lines.

And yet I commonly see discussion of current in transmission
lines. Current is charge flow per unit time. Is this all
invalid? Must we abondon measurements of current? Voltage?
These are all based on the assumption of charge being
a useful concept.

...Keith

Standing-Wave Current vs Traveling-Wave Current
 

On Jan 3, 1:25*pm, Cecil Moore wrote:
For the record: The only controversial assertion
that I have ever made is that coherent EM wave
cancellation can cause a redistribution of the
EM energy in the opposite direction in a transmission
line.

Don't be so modest.

You have also claimed that for an amplifier which can
be modelled as a Thevenin or Norton equivalent circuit,
the output impedance can not be used to derive the
reflection coefficient.

You have claimed that the only way to prevent a
re-reflection at a generator is to use a circulator;
a 10 cent resistor will never do.

You have claimed that energy can cross a point on
the line where V or I is always 0.

You have claimed that there is great importance
to the terms "Traveling-Wave Current" and
"Standing-Wave Current" (the title of this thread).

And there were more that escape my memory.

...Keith

Standing-Wave Current vs Traveling-Wave Current
 

On Jan 3, 2:14*pm, Jim Kelley wrote:
Keith Dysart wrote:
The example was carefully chosen to illustrate the
point, of course. But that is the value of particular
examples.
When the pulses are not identical, the energy that crosses
the point is exactly sufficient to turn one pulse
into the other.
The remainder of the energy must bounce
because it does not cross the mid-point.
...Keith

So it really is almost as though the pulses travel through one
another, rather than bounce off one another.

I have seen the concept that energy doesn't cross nodal points alluded
to in some texts. *However there are so many exceptions to it found in
physical systems as to render it a dubious notion at best. Useful
perhaps for illustration purposes.

In the discussion of standing waves on a string, Halliday and Resnick
says "It is clear that energy is not transported along the string to
the right or to the left, for energy cannot flow past the nodal points
in the string, which are permanently at rest. *Hence the energy
remains "standing" in the string, although it alternates between
vibrational kinetic energy and elastic potential energy."

So the idea is valid for a simple harmonic oscillator in which there
are no losses. *In such a case, once the system begins oscillating, no
further input of energy is required in order to maintain oscillation.
* Clearly there is no flow of energy into or out of such a system.
What is clear is that energy doesn't pass through the nodes. *It is
less clear that there exists an inherent mechanism which prevents the
movement of energy.

And so it appears in cases where there is no transfer of energy that
one might claim that waves bounce off of one another. *There are no
other examples, and no supporting mechanism for it of which I am
aware, and so one might be equally justified in claiming that waves
pass through each other in all cases.

I'd suggest that this is only if the concept of the
waves in question does not include energy. In the
limiting case of the two waves being identical no
energy crosses the nodes. In other cases, only a
portion of the energy crosses the nodes.

If the concept of the waves includes energy, some
explanation is required to account for the wave
crossing the node, but its energy does not.

Some readers like to superpose energy just as
they do voltage, but in general this is not a
valid operation so I am uncomfortable using
it as the explanation.

...Keith

Standing-Wave Current vs Traveling-Wave Current
 

"Keith Dysart" wrote in message
...

Sorry i have been absent for a while, been too busy with other work and had
to turn this off to keep from spending all my time laughing at the postings.
Are we going for another 1000 post thread? almost 2/3's of the way there
now... here is a kick to keep it going.

You have claimed that energy can cross a point on
the line where V or I is always 0.

ah, so once you have a standing wave on a line then no energy can cross the
voltage or current nodes?? thats interesting. so at the place where
current is 'always' 0 the voltage is a max right? so what happens to the
V^2/Z power at that point? is that not flowing past that point?
conversely, at the point where voltage is always zero, what happens to the
large I^2*R power at that point??? where does that go? then try this
thought experiment... take a long coax with an open circuit end, feed it
with sinusoidal ac so it has nice standing waves, keep it lossless just
because that irritates some of the writers on here. then attach a pure
resistance equal to Z0 at the open end. now, if energy can't pass the
points where V or I is zero, and I is obviously zero at the open circuit at
the end of the line there should be no power to flow into that resistor???
Oh, but wait, the voltage is a max there so the resistor could draw power
from the voltage standing wave, but then what happens to the current
standing wave? once the resistor drains the last half wave voltage wave how
does energy get from the next standing wave into the far end one to
replenish it if it can't flow across the voltage node?? sorry, i have to
stop, about to start another laughing fit.

all of the above obvious contradictions become intuitively obvious once you
completely forget the standing waves and think only in terms of the
traveling waves. and remember, again just because it tweaks some
correspondents on here, you only need the voltage OR the current traveling
wave, either one is sufficient to completely describe the conditions on the
line in either steady state or transient conditions. (as long as the line
and components are all linear and time invarient, loss is not a problem for
this statement to be true)

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
And yet I commonly see discussion of current in transmission
lines.

RF current is a *result* of the H-field in the EM
wave. There are photons involved making it different
from DC. Electrons may (or may not) "bounce" off of
each other but photons traveling in opposite directions
in a transmission line do not and cannot "bounce" off
of each other. They pass each other like ships in the
night. Any theory based on photons "bouncing" off of
each other while traveling in opposite directions, is
inaccurate and doomed to failure. Simply applying the
scientific method will remedy the problem.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

cecil scribbled:
RF current is a *result* of the H-field in the EM wave. There are photons
involved making it different from DC.

which comes first, the current or the field? i contend that it is not
necessary to consider the current or the h-field at all. use the voltage
traveling wave and it is not necessary to consider current at all, hence
where does the h-field come from? or consider the current traveling wave
and then where does the e-field come from? forget photons when thinking of
coax, antennas, currents, and waves, they will just confuse you.

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
You have also claimed that for an amplifier which can
be modelled as a Thevenin or Norton equivalent circuit,
the output impedance can not be used to derive the
reflection coefficient.

And have proved it with concepts that existed before
I was born. I cannot take credit for that.

If an amplifier is delivering zero net power, the
calculated rho = SQRT(Pref/Pfor) = plus or minus 1.0
The value of the "output impedance" is irrelevant.
Because of superposition, the reflected energy never
encounters the "output impedance".

You have claimed that the only way to prevent a
re-reflection at a generator is to use a circulator;
a 10 cent resistor will never do.

Roy has said essentially the same thing in so many
words. You see, your concepts lead to a direct
violation of the conservation of energy principle
for which I can take no credit.

You have claimed that energy can cross a point on
the line where V or I is always 0.

Since it is impossible for photons to reflect while
traveling in a homogeneous medium, that one is a
no-brainer. I cannot take credit for anything I
learned from Quantum Electrodynamics.

You have claimed that there is great importance
to the terms "Traveling-Wave Current" and
"Standing-Wave Current" (the title of this thread).

Again, I didn't invent standing wave current and
traveling wave current. I am just reporting what
I have learned from people who knew the difference
before I was born. If one knows much of anything about
mathematics, one can look at the equation for standing
wave current and the equation for traveling wave current
and see the considerable differences. That you cannot
just proves that you don't know much of anything about
mathematics.

Standing wave current = Io*cos(kx)*cos(wt)

Traveling wave current = Io*cos(kx+wt)

I feel sorry for any "technical" person who cannot see
the difference. For traveling waves, the position and
phase are interlocked. For standing waves, the position
and phase are divorced. Those differences are obvious
and are plotted at.

http://www.w5dxp.com/travstnd.gif
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
Some readers like to superpose energy just as
they do voltage, but in general this is not a
valid operation so I am uncomfortable using
it as the explanation.

Optical physicists have been "adding" power
densities (irradiance) for centuries. It's past
time for you to learn how they did it.
--
73, Cecil http://www.w5dxp.com