Standing-Wave Current vs Traveling-Wave Current
 

Gene Fuller wrote:
"Way back" is irrelevant. One only needs to open a serious text book on
Optics, such as Born and Wolf, to see how optical physicists perform
analysis today.

The readers may be interested in how it is done today.
Please tell us how the phase of light is measured today.

What you might also notice in AN 95-1 is that there
is no mention of incident and reflected ...

Sorry Gene, I'm tired of wasting my time proving that you
are lying. Anyone who wants to prove how unethical you are
can do so by accessing:

http://www.ecs.umass.edu/ece/labs/an...parameters.pdf

and searching for "incident" and "reflected".
Lots of unethical BS deleted after that.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Roy Lewallen wrote:
I heartily second Keith's recommendations.

Of course you two want to deny that reflected waves
contain any energy at all. If there is any energy
in reflected waves, your house-of-cards collapses.

So Roy, please explain how all those reflected
waves that are incident upon your optic nerves
don't contain any energy. (I'm not going to hold
my breath for your answer.)
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Gene Fuller wrote:
The
electromagnetic theory for optics (e.g. somewhere in the vicinity of
visible light) is of course identical to the electromagnetic theory for
HF.

Thanks Gene, I never thought you would ever admit that
fact of physics. Now that you have, your entire argument
collapses. If interference can happen in free space, it
certainly can happen in a transmission line.

I have a couple of editions of Born and Wolf, which is a high level
reference and often considered the standard for optics. I have been
unable to find even one mention of "constructive" or "destructive"
interference in their writing.

Try "Optics" by Hecht. He devotes an entire chapter
to interference. Hecht mentions destructive and constructive
interference dozens of times. I can quote page after page
of such if you want me to. Feel free to dispute Hecht if
you want, but that is your problem, not mine.

Of course they delve into the topic of
interference in excruciating detail. They don't, however, ascribe any
particular mysticism or magic to interference. It is simply what happens
when the wave fields are superposed.

Neither do I. It is just what happens when the wave fields
are superposed. The destructive interference must balance
the constructive interference to avoid violation of the
conservation of energy principle.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

I'm top posting this so readers won't have to scroll down to see it, but
so I can include the original posting completely as a reference.


Keith, you've presented a very good and well thought out argument. But
I'm not willing to embrace it without a lot of further critical thought.
Some of the things I find disturbing a

1. There are no mathematics to quantitatively describe the phenomenon.
2. I don't understand the mechanism which causes waves to bounce.
3. No test has been proposed which gives measurable results that will
be different if this phenomenon exists than if it doesn't. (I
acknowledge your proposed test but don't believe it fits in this category.)
4. I'm skeptical that this mechanism wouldn't cause visible
distortion when dissimilar waves collide. But without any describing
mathematics or physical basis for the phenomenon, there's no way to
predict what should or shouldn't occur.
5. Although the argument about no energy crossing the zero-current
node is compelling, I don't feel that an adequate argument has been
given to justify the wave "bouncing" theory over all other possible
explanations.

None of these make an argument with your logical development, although I
think I might be able to do that too. But I'm very reluctant to accept a
view of wave interaction that's apparently contrary to established and
completely successful theory and one, if true, might have profound
effects on our understanding of how things work. So frankly I'm looking
hard for a flaw in your argument. And I may have found one.

A large part of the argument seems to revolve around a single point in a
perfect transmission line, where the current is exactly zero. This is an
infinitesimal point on a perfect line, so some anomalous things might be
expected to happen there.

Let's consider a transmission line as a huge number of series inductors
and shunt capacitors, each an ideal lumped device. In the ideal case, of
course, there would be an infinite number of each, and each would have
an infinitesimal value. However, the LC product and ratio must remain
correct even in the limiting case. Each L and C is an ideal device, so
the current into one terminal of an inductor has to equal the current
out of the other. A consequence of this is that either we have a whole
inductor with zero current, or the zero current point occurs between
inductors, at a node to which a capacitor is connected. I think we'll
get the same result using either scenario, but let's consider the second.

If we analyze this situation carefully, we'll find that the inductor on
each side of the zero-current point does have a finite current, equal in
amplitude and flowing in opposite directions. So for half of the cycle,
both are putting positive charge in the capacitor, and for the other
half of the cycle, both are removing charge. The capacitor voltage goes
up and down as a result, as we can also see by looking at the voltage at
this zero-current point. So current from both sides is contributing to
the capacitor charge, and turning off either one would change the line
conditions. Any change in the current from the inductor on one side
would change the capacitor voltage, and hence the current on the other
side. So there is an interchange of information from one side to the
other. Each inductor is conveying energy to the capacitor, which is
storing and returning it.

Ok, so let's break the capacitor into two, each being half the original
value, and constrain each inductor to deliver charge only to "its"
capacitor. The wire between the capacitors carries no current because
the capacitors always have equal voltages, and can be cut with no effect.

When there was one capacitor, it shared energy from both sides. When we
broke it into two, there was no mixing of energy from either side. Why
might one be a better description of reality than the other? It looks to
me like the argument devolves into speculation about how small the
"point" is at which the current drops to zero.

It would be instructive to see what happens as, for example, the load
resistance is increased toward infinity or decreased toward zero
arbitrarily closely, but not at the point at which it's actually there.
If the "bouncing" phenomenon is necessary only to explain the limiting
case of infinite SWR on a perfect line but no others, then an argument
can be made that it's not necessary at all. I suspect this is the case.

I agree with your argument about two sources energized in turn, and have
used that argument a number of times myself to refute the notion of
superposing powers. Once two voltage or current waves occupy the same
space, the only reality is the sum. We're free to split them up into
traveling waves or any other combination we might dream up, with the
sole requirement being that the sum of all our creations equals the
correct total. (And the behavior of waves you're describing seemingly go
beyond this.) The advantage to the non-interacting traveling wave model
is that it so neatly predicts transient phenomena such as TDR and run-up
to steady state. I spent a number of years designing TDR circuitry,
interfacing with customers, and on several occasions developing and
teaching classes on TDR techniques, without ever encountering any
phenomena requiring explanations beyond classical traveling wave theory.
So you can understand my reluctance to embrace it based on a problem
with energy transfer across a single infinitesimal point in an ideal line.

Roy Lewallen, W7EL

Keith Dysart wrote:
On Dec 30 2007, 6:18 pm, Roy Lewallen wrote:
Keith Dysart wrote:

I predict that the pulse arriving at the left end will
have the same voltage, current and energy profile as
the pulse launched at the right end and the pulse
arriving at the right end will be similar to the
one launched at the left.
They will appear exactly AS IF they had passed
through each other.
The difficulty with saying THE pulses passed
through each other arises with the energy. The
energy profile of the pulse arriving at the left
will look exactly like that of the one launched
from the right so it will seem that the energy
travelled all the way down the line for delivery
at the far end. And yet, from the experiment above,
when the pulses arriving from each end have the
same shape, no energy crosses the middle of the
line.
So it would seem that the energy that actually
crosses the middle during the collision is
exacly the amount of energy that is needed to
reconstruct the pulses on each side after the
collision.
If all the energy that is launched at one end
does not travel to the other end, then I am
not comfortable saying that THE pulse travelled
from one end to the other.
But I have no problem saying that the system
behaves AS IF the pulses travelled from one
end to the other.
You said that:

What will happen? Recall one of the basics about
charge: like charge repel. So it is no surprise
that these two pulses of charge bounce off each
and head back from where they came.

Yet it sounds like you are saying that despite this charge repulsion and
bouncing of waves off each other, each wave appears to be completely
unaltered by the other? It seems to me that surely we would detect some
trace of this profound effect.

. . .
Is there any test you can conceive of which would produce different
measurable results if the pulses were repelling and bouncing off each
other or just passing by without noticing the other?

There are equations describing system behavior on the assumption of no
wave interaction, and these equations accurately predict all measurable
aspects of line behavior without exception. Have you developed equations
based on this charge interaction which predict line behavior with
equal accuracy and universal applicability?

No equations. I expect that such equations would be more complex
than those describing the behaviour using superposition. Since
the existing equations and techniques for analysis are tractable
and produce accurate results, I am not motivated to develop an
alternate set with lower utility.

And yet the "no interaction" model, while accurately predicting
the behaviour has some weaknesses with explaining what is
happening. It is, I suggest, these weaknesses that help lead
some so far astray.

To illustrate some of these weaknesses, consider an example
where a step function from a Z0 matched generator is applied
to a transmission line open at the far end. Charge begins to
flow into the line. The ratio of the current to voltage on
the line is defined by the distributed inductance and
capacitance. The inductance is resisting the change in current
which causes a voltage to charge the capacitance. A voltage
step (call this V for later use) propagates down the line
at the speed of light. In front of this step, the voltage,
current and charge in the line is zero. After the step, the
capacitance is charged to the voltage and charge is flowing
in the inductance.

The step function eventually reaches the open end where
the current can no longer flow. The inductance insists
that the current continue until the capacitance at the
end of the line is charged to the voltage which will stop
the flow. This voltage is double the voltage of the step
function applied to the line (i.e 2*V). Once the
infinitesimal capacitance at the end of the line is
charged, the current now has to stop just a bit earlier
and this charges the inifinitesimal capacitance a bit
further from the end. So a step in the voltage propagates
back along the line towards the source. In front of this
step, current is still flowing. Behind the step, the
current is zero and voltage is 2*V. The charge that
is continuing to flow from the source is being used
to charge the distributed capacitance of the line.

The voltage that is propagating backwards along the
line has the value 2*V, but this can also be viewed as
a step of voltage V added to the already present voltage
V. The latter view is the one that aligns with the "no
interaction" model; the total voltage on the line is
the sum of the forward voltage V and the reverse
voltage V or 2*V.

In this model, the step function has propagated to the
end, been reflected and is now propagating backwards.
Implicit in this description is that the step continues
to flow to the end of the line and be reflected as
the leading edge travels back to the source.

And this is the major weakness in the model. It claims
the step function is still flowing in the portion of
the line that has a voltage of 2*V and *zero* current.

Now without a doubt, when the voltages and currents
of the forward and reverse step function are summed,
the resulting totals are correct. But it seems to
me that this is just applying the techniques of
superposition. And when we do superposition on a
basic circuit, we get the correct totals for the
voltages and currents of the elements but we do
not assign any particular meaning to the partial
results.

A trivial example is connecting to 10 volt batteries
in parallel through a .001 ohm resistor. The partial
results show 10000 amps flowing in each direction
in the resistor with a total of 0. But I do not
think that anyone assigns significance to the 10000
amp intermediate result. Everyone does agree that
the actual current in the resistor is zero.

The "no interaction" model, while just being
superposition, seems to lend itself to having
great significance applied to the intermediate
results.

Partially this may be due to poor definitions. If the
wave is defined as just being a voltage wave, then
all is well.

But, for example, when looking at a solitary pulse,
it is easy (and accurate) to view the wave as having
more than just voltage. One can compute the charge,
the current, the power, and the energy. But when
two waves are simultaneously present, it is only
legal to superpose the voltage and the current.
But it is obvious that a solitary wave has voltage,
current, power, etc. But when two waves are present
it is not legal to.... etc., etc.
The "no interaction" model does not seem to resolve
this conflict well, and some are lead astray.

And it was this conflict that lead me to look for
other ways of thinking about the system.

Earlier you asked for an experiment. How about this
one....

Take two step function generators, one at each end
of a transmission line. Start a step from each end
at the same time. When the steps collide in the
middle, the steps can be viewed as passing each
other without interaction, or reversing and
propagating back to their respective sources. We
can measure the current at the middle of the line
and observe that it is always 0. Therefore the
charge that is filling the capacitance and causing
the voltage step which is propagating back towards
each generator must be coming from the generator
to which the step is propagatig because no charge
is crossing the middle of the line.

Do you like it?

...Keith

Standing-Wave Current vs Traveling-Wave Current
 

Jim Kelley wrote:

It's fairly safe to make this argument when both pulses are identical.
I challenge you to obtain this result when they are not. :-)

73, Jim AC6XG

I proposed this some time ago, and got the response that dissimilar
pulses would still bounce off each other, yet appear exactly as though
they were passing through without interaction. I haven't been able to
understand why this would be, but there are no mathematics to explain it.

Roy Lewallen, W7EL

Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:
Jim Kelley wrote:

That is a question more typically asked by someone who has never taken
a calculus class.


The answer is typically asserted by someone who doesn't
know the difference between joules and joules per second.

Or so it might seem to someone who had neglected to consider that the
'per second' in Joules per second in this case derives from the rate
at which charge is moving.

73, ac6xg

Standing-Wave Current vs Traveling-Wave Current
 

On Wed, 02 Jan 2008 16:38:36 -0800, Roy Lewallen
wrote:

2. I don't understand the mechanism which causes waves to bounce.

If I might amplify a similar concern.

Bounce is a phenomenon in everbody's experience, hence the term easily
clouds the conversation as it also not a very rigorous term in RF.

In the day to day world of, say, rubber balls, bounce implies:
1. an inelastic deformation upon collision;
2. the conversion of kinematic energy into potential energy;
3. a period or interval of holding that potential energy (or further
accumulation of potential energy);
4. the cessation of the inelastic deformation and the rebound
unwinding 1-3 above as potential energy is converted back into
kinematic energy.

So, for this "bounce" in a wave, can I observe the inelastic
deformation? (Not just the superposition of waves, but the actual
inelastic crush against resistance.) Inelastic often has loss
attending it, do you care to characterize it as elastic? If so, then
the usage of "bounce" is running against the grain of popular usage.

In this "bounce" in a wave, can I observe the time interval during
which kinematic energy is converted to potential energy and then back
to kinematic energy? (Is there a retardation in the wave migration? I
would suspect a phase change might reveal this, and not just a phase
inversion, nor a phase reversal.)

73's
Richard Clark, KB7QHC

Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:
Gene Fuller wrote:

What you might also notice in AN 95-1 is that there is no mention of
incident and reflected ...

Sorry Gene, I'm tired of wasting my time proving that you
are lying. Anyone who wants to prove how unethical you are
can do so by accessing:

http://www.ecs.umass.edu/ece/labs/an...parameters.pdf

and searching for "incident" and "reflected".
Lots of unethical BS deleted after that.

I guess I must be hitting close to target. You always get nasty when I
create problems for your pet theories.

Thanks for the reference to AN 95-1, even though I have several copies
already. Your directed search terms prove my point exactly. I suppose
puncturing your balloon is "unethical", but that is your problem, not mine.

I challenged you to find any case in AN 95-1 that supports your claim of
counter-traveling waves in a transmission line, with each wave carrying
its own energy that somehow nets out to zero. You came up with exactly
nothing, which is not surprising.

Ranting and raving does not have any impact on the correct physical
reality.

Oh, by the way, my full comment was, ". . . there is no mention of
incident and reflected waves on a transmission line, each carrying
energy (or power or whatever you prefer), and passing like ships in the
night."

Your careful trimming is noted.

73,
Gene
W4SZ

Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:
Gene Fuller wrote:
The electromagnetic theory for optics (e.g. somewhere in the vicinity
of visible light) is of course identical to the electromagnetic theory
for HF.

Thanks Gene, I never thought you would ever admit that
fact of physics. Now that you have, your entire argument
collapses. If interference can happen in free space, it
certainly can happen in a transmission line.


Cecil,

No one has ever said anything different. No one has ever denied
interference.

You are really grasping at straws now.

73,
Gene
W4SZ

Standing-Wave Current vs Traveling-Wave Current
 

On 2 Jan, 16:38, Roy Lewallen wrote:
I'm top posting this so readers won't have to scroll down to see it, but
so I can include the original posting completely as a reference.

Keith, you've presented a very good and well thought out argument. But
I'm not willing to embrace it without a lot of further critical thought.
Some of the things I find disturbing a

* *1. There are no mathematics to quantitatively describe the phenomenon.
* *2. I don't understand the mechanism which causes waves to bounce.
* *3. No test has been proposed which gives measurable results that will
be different if this phenomenon exists than if it doesn't. (I
acknowledge your proposed test but don't believe it fits in this category.)
* *4. I'm skeptical that this mechanism wouldn't cause visible
distortion when dissimilar waves collide. But without any describing
mathematics or physical basis for the phenomenon, there's no way to
predict what should or shouldn't occur.
* *5. Although the argument about no energy crossing the zero-current
node is compelling, I don't feel that an adequate argument has been
given to justify the wave "bouncing" theory over all other possible
explanations.

None of these make an argument with your logical development, although I
think I might be able to do that too. But I'm very reluctant to accept a
view of wave interaction that's apparently contrary to established and
completely successful theory and one, if true, might have profound
effects on our understanding of how things work. So frankly I'm looking
hard for a flaw in your argument. And I may have found one.

A large part of the argument seems to revolve around a single point in a
perfect transmission line, where the current is exactly zero. This is an
infinitesimal point on a perfect line, so some anomalous things might be
expected to happen there.

Let's consider a transmission line as a huge number of series inductors
and shunt capacitors, each an ideal lumped device. In the ideal case, of
course, there would be an infinite number of each, and each would have
an infinitesimal value. However, the LC product and ratio must remain
correct even in the limiting case. Each L and C is an ideal device, so
the current into one terminal of an inductor has to equal the current
out of the other.

That is not correct. If both the capacitor and the inductance are
ideal
they cannot return the same amount of energy. This can only happen
when the
summation of all vectors are parallel to the axis of the conductor.
One only has to look at the vectors involved with out assigning length
to the vectors to see that the vectorial summation cannot be parallel
to the radiator axis. This is exactly why for maximum horizontal gain
the radiator is tipped away from the earth's surface. This response
is clearly shown when a time varient is added to Gaussian law.




A consequence of this is that either we have a whole
inductor with zero current, or the zero current point occurs between
inductors, at a node to which a capacitor is connected. I think we'll
get the same result using either scenario, but let's consider the second.

If we analyze this situation carefully, we'll find that the inductor on
each side of the zero-current point does have a finite current, equal in
amplitude and flowing in opposite directions. So for half of the cycle,
both are putting positive charge in the capacitor, and for the other
half of the cycle, both are removing charge.

That can only be true for a full wave radiator which emulates
a tank circuit. A half wave radiator is a series circuit,
a whole different ball game !





The capacitor voltage goes
up and down as a result, as we can also see by looking at the voltage at
this zero-current point. So current from both sides is contributing to
the capacitor charge, and turning off either one would change the line
conditions.

Not at the change over point where voltages are equal since a
capacitor
has a slight delay before discharging because of initial inductance
delay.



Any change in the current from the inductor on one side
would change the capacitor voltage, and hence the current on the other
side. So there is an interchange of information from one side to the
other. Each inductor is conveying energy to the capacitor, which is
storing and returning it.

It takes energy to propagate does it not?
Why would you ignore that?

Ok, so let's break the capacitor into two, each being half the original
value, and constrain each inductor to deliver charge only to "its"
capacitor. The wire between the capacitors carries no current because
the capacitors always have equal voltages, and can be cut with no effect.
Again that cannot be. The filling of all the capacitors fill up in a
series format.
snip
Art



Roy Lewallen, W7EL



Keith Dysart wrote:
On Dec 30 2007, 6:18 pm, Roy Lewallen wrote:
Keith Dysart wrote:

I predict that the pulse arriving at the left end will
have the same voltage, current and energy profile as
the pulse launched at the right end and the pulse
arriving at the right end will be similar to the
one launched at the left.
They will appear exactly AS IF they had passed
through each other.
The difficulty with saying THE pulses passed
through each other arises with the energy. The
energy profile of the pulse arriving at the left
will look exactly like that of the one launched
from the right so it will seem that the energy
travelled all the way down the line for delivery
at the far end. And yet, from the experiment above,
when the pulses arriving from each end have the
same shape, no energy crosses the middle of the
line.
So it would seem that the energy that actually
crosses the middle during the collision is
exacly the amount of energy that is needed to
reconstruct the pulses on each side after the
collision.
If all the energy that is launched at one end
does not travel to the other end, then I am
not comfortable saying that THE pulse travelled
from one end to the other.
But I have no problem saying that the system
behaves AS IF the pulses travelled from one
end to the other.
You said that:

* What will happen? Recall one of the basics about
* charge: like charge repel. So it is no surprise
* that these two pulses of charge bounce off each
* and head back from where they came.

Yet it sounds like you are saying that despite this charge repulsion and
bouncing of waves off each other, each wave appears to be completely
unaltered by the other? It seems to me that surely we would detect some
trace of this profound effect.

. . .
Is there any test you can conceive of which would produce different
measurable results if the pulses were repelling and bouncing off each
other or just passing by without noticing the other?

There are equations describing system behavior on the assumption of no
wave interaction, and these equations accurately predict all measurable
aspects of line behavior without exception. Have you developed equations
* based on this charge interaction which predict line behavior with
equal accuracy and universal applicability?

No equations. I expect that such equations would be more complex
than those describing the behaviour using superposition. Since
the existing equations and techniques for analysis are tractable
and produce accurate results, I am not motivated to develop an
alternate set with lower utility.

And yet the "no interaction" model, while accurately predicting
the behaviour has some weaknesses with explaining what is
happening. It is, I suggest, these weaknesses that help lead
some so far astray.

To illustrate some of these weaknesses, consider an example
where a step function from a Z0 matched generator is applied
to a transmission line open at the far end. Charge begins to
flow into the line. The ratio of the current to voltage on
the line is defined by the distributed inductance and
capacitance. The inductance is resisting the change in current
which causes a voltage to charge the capacitance. A voltage
step (call this V for later use) propagates down the line
at the speed of light. In front of this step, the voltage,
current and charge in the line is zero. After the step, the
capacitance is charged to the voltage and charge is flowing
in the inductance.

The step function eventually reaches the open end where
the current can no longer flow. The inductance insists
that the current continue until the capacitance at the
end of the line is charged to the voltage which will stop
the flow. This voltage is double the voltage of the step
function applied to the line (i.e 2*V). Once the
infinitesimal capacitance at the end of the line is
charged, the current now has to stop just a bit earlier
and this charges the inifinitesimal capacitance a bit
further from the end. So a step in the voltage propagates
back along the line towards the source. In front of this
step, current is still flowing. Behind the step, the
current is zero and voltage is 2*V. The charge- Hide quoted text -

- Show quoted text -...

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