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On Apr 9, 3:03*pm, Roy Lewallen wrote:
Keith Dysart wrote:
On Apr 8, 8:51 am, Cecil Moore wrote:
. . .
The
forward wave flows unimpeded through the node as does
the equal magnitude reflected wave. The net energy flow
is zero. The average energy flow is zero.

Anyone who believes there is zero energy at a standing-
wave current node should touch that point on a transmission
line (which just happens to be the same point as the
maximum voltage anti-node).

No one has said there is zero energy. Only that there is
zero energy flow. For energy flow, one needs simultaneous
voltage and current.
. . .

In the interesting case of a current node on an infinite-SWR line, it
appears we do have energy flow without any current, and therefore
without power. Energy flows into the node from both directions in equal
amounts at the same time, and out to both directions in equal amounts at
the same time.

I think I would be tempted to cut the node down the middle creating
two nodes with no current flow or energy flow between them.

What we don't have is *net* energy flow at the node.
Likewise, there's charge flowing into the node from both directions, and
out in both directions, which results in the zero net current. I don't
believe that's the same as saying there's no energy or charge flow at
all, even though the power and current are zero. And it's not necessary
to separately consider forward and reverse waves of current, energy, or
power in order to observe this -- it can be seen from looking only at
the total charge or energy.

One thought experiment I rather like is the infinite SWR ideal line.
Cut the line at all the current zeroes. The voltage, current, and,
I'd suggest, the energy distribution do not change. The line can
be re-assembled, again with no change.

Those who argue that energy is crossing the node, have to explain that
the cut has completely changed the mechanism that keeps the net energy
in its place, but the voltage and current distributions remain the
same. I prefer the basic circuit theory tenet that one can cut a
line carrying no current without impacting the circuit. This leads
to a model with no energy crossing the node.

...Keith

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On Apr 9, 12:29*pm, Cecil Moore wrote:
Keith Dysart wrote:
Thus I strongly suggest that Vg, Ig, Pg, represent reality. The
others are a convenient alternative view for the purposes of
solving problems.

Of course they represent *net* reality but we are trying
to determine what is happening at a component wave level.
Defining the component waves out of existence is an un-
acceptable substitute for ascertaining what is happening
in reality.

Typically we see Vg split into Vf and Vr, but why stop at two.
Why not 3, or 4?

Because two is what a directional wattmeter reads. The
two superposed waves, forward and reverse, can be
easily distinguished from one another. Two superposed
coherent forward waves cannot be distinguished from
each other. That's why we stop at two - because it is
foolish to go any farther.

You sometimes use three. Discussions of ghosts have at
least three. Not so foolish, methinks.

There is power coming from the transmission line. Looking at Pg(t),
some of the time energy flows into the line, later in the cycle
it flows out. The energy transfer would be exactly the same if the
transmission line was replaced by a lumped circuit element. And
we don't need Pf and Pr for an inductor.

OTOH, the distributed network model is a superset of
the lumped circuit model so the inadequate lumped
circuit model might confuse people. Hint: changing
models to make waves disappear from existence doesn't
make the waves disappear.

The model is not inaccurate when the question is framed
with the model, as you do for Fig 1-1.

The lumped circuit model is adequate for lumped circuits.
It is inadequate for a lot of distributed network problems.
If the lumped circuit model worked for everything, we
wouldn't ever need the distributed network model.

True, but the question at hand, based on Fig 1-1 is lumpy.

I suggest that you take your circuit and apply distributed
network modeling techniques to it including reflection
coefficients and forward and reflected voltages, currents,
and powers at all points in the circuit. Note that the
reflections are *same-cycle* reflections. If the lumped
circuit model analysis differs from the distributed network
model analysis, the lumped circuit analysis is wrong.

Ummm. It was your circuit.

It goes up because the impedance presented by the transmission
changes when the reflection returns. This change in impedance
alters the circuit conditions and the power in the various
elements change. Depending on the details of the circuit,
these powers may go up, or they may go down when the reflection
arrives.

That is true, but the impedance is *VIRTUAL*, i.e. not an
impedor, and is therefore only an *EFFECT* of superposition.
We are once again left wondering about the *CAUSE* of the
virtual impedance, i.e. the details of the superposition
process. Ignoring those details will not solve the problem.

Actually, the transmission line input impedance is quite real,
formed from distributed capacitance and inductance. Like most two
terminal circuits, it can be reduced to simpler form.

...Keith

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On Apr 9, 12:59*pm, Cecil Moore wrote:
Keith Dysart wrote:
Cecil Moore wrote:
There is no capacitance or inductance in the source to
store energy.

"In" is an oxymoron for the lumped circuit model.
The lumped reactance exists *at* the same point as
the source because everything is conceptually lumped
into a single point.

In the real world, circuits are never single points
and there exists a frequency at which distributed
network effects cannot be ignored. In reality,
distributed network effects occur for all real
circuits but they can often be ignored as negligible.

The two inches of wire connecting the source to the
source resistor has a characteristic impedance and
is a certain fraction of a wavelength long. If it is
not perfectly matched, reflections will occur, i.e.
there will exist forward power and reflected power on
that two inches of wire.

It was your Fig 1-1, made of ideal elements with none
of these issues.

For the 1/8WL
shorted line, there appears to be 125 watts of forward
power and 25 watts of reflected power at points on each
side of the source.

Not if there is no transmission line.

Aha, there's your error. What would a Bird directional
wattmeter read for forward power and reflected power?
Consider that short pieces of 50 ohm coax are used
to connect the real-world components together.

It would read something completely different if it was
calibrated for 75 ohms, though the difference between
Pf and Pr would be the same.

But that is not the circuit of your Fig 1-1.

Or chose any characteristic impedance and do the math.
You will discover something about the real world, i.e.
that you have been seduced by the lumped circuit model.

It was your circuit; Fig 1-1.

Perhaps. *But I don't need more examples where the
powers balance. I already have the one example where
they don't.

And that one example is outside the scope of the
preconditions of my Part 1 article. Let me help you
out on that one. There are an infinite number of
examples where the reflected power is NOT dissipated
in the source resistor but none of those examples,
including yours, satisfies the preconditions specified
in my Part 1 article. Therefore, they are irrelevant
to this discussion.

As long as you agree that the imputed energy in the
reflected wave is not dissipated in the source
resistor; and only claim that the imputed average
power in the reflected wave is numerically equal
to the increase in the dissipation.


But there are no component powers in the source. It
is a simple circuit element.

No wonder your calculations are in error.
Perform your calculations based on the readings of
an ideal 50 ohm directional wattmeter and get back to us.

Well there's a plan. Measure everything in a
circuit with a directional wattmeter. You first.
Start with Fig 1-1.

But you'll have to choose the calibration impedance.

I'd suggest 100 ohms for the section between the
source and the source resistor because the source
resistor and the line initially present a 100 ohm
impedance and you would not want any reflections
messing up the measurements.

Hint: Mismatches cause reflections, even in real-world
circuits. The reflections happen to be *same-cycle*
reflections. The simplified lumped circuit model, that
exists in your head and not in reality, ignores those
reflections and thus causes confusion among the
uninitiated who do not understand its real-world
limitations.

We should explore this new world. Please discard your
voltmeter, ammeter, oscilloscope, .... All you need
is a Bird wattmeter.

...Keith

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Keith Dysart wrote:
On Apr 9, 12:51 pm, Roger Sparks wrote:
. . .
So far as breaking Vg into many sequential/different Vf and Vr, we usually need to do that. Cecil chose our simple example to prevent re-reflection (reflection of the reflection) but even then it is apparent that the voltage source will have a reactive component.

I still think of a voltage source as just being a voltage source, not
something
with resitance, reactance or impedance.
. . .

An ideal voltage source has, by definition, zero impedance, which means
zero resistance and zero reactance. No amount of current you put into it
or take out of it will alter its voltage. The ratio of voltage to
current at its terminals is the impedance of the load which the source
sees, not the impedance of the source. If a source used in an analysis
has finite resistance, it's not an ideal voltage source.

Roy Lewallen, W7EL

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Keith Dysart wrote:
One thought experiment I rather like is the infinite SWR ideal line.
Cut the line at all the current zeroes. The voltage, current, and,
I'd suggest, the energy distribution do not change. The line can
be re-assembled, again with no change.

When you cut the line, you introduce an open circuit
where none existed before. Everything obeys the
distributed network model, at least conceptually.

Before you cut the line, there is no physical
impedance discontinuity and therefore no
reflections. You have to invent complete new
laws of physics for that one. I'm not against
you inventing new laws of physics but you need
to invent them before, not after, you use them. :-)
--
73, Cecil http://www.w5dxp.com

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On Apr 9, 1:22*pm, Cecil Moore wrote:
Keith Dysart wrote:
On Apr 8, 8:51 am, Cecil Moore wrote:
Roy Lewallen wrote:
Now, I don't know of any way to assign "ownership" to bundles of energy.
One way is to add a unique bit of modulation to each
bundle of wave energy. I am fond of using a TV signal
and observing ghosting on the screen. This, of course,
assumes that the modulation stays with the same component
wave to which it was originally associated.

But as soon as you modulate, you no longer have sinusoidal
steady state.

You know and I know that is a copout diversion to avoid
your having to face the technical facts.

You seem to be the one who knows this. I don't.

Consider the 1 second interval from 4.5 to 5.5 seconds.
In this second 0.016393 joules flow for an average
power of 0.016393 W. But the sum of the imputed power
in the two spectral components is 1 W. Where did the
missing energy go?

Hint: Missing energy is impossible except in your mind.
Just because you are ignorant of where the energy goes
doesn't mean it is missing. It just means that you fail
to understand interference. Have you not read Hecht's
Chapter 9 on "Interference"?

Obviously, interference is present and there is *NO*
missing energy. I have previously listed the possibilities
at least four times so will not bother listing them again.

Between 9.5 and 10.5 seconds, 1.983607 J (average 1.983607 W)
of energy flows. By 'interference', I think you are suggesting
the missing power from 4.5 to 5.5 appears as excess power
between 9.5 and 10.5, thus satisfying your conservation of
energy requirement. But where was the energy stored for
5 seconds until it could be delivered.

Or, more intriguing, between 0 and 1 second, 1.935466 J
(average 1.935466 W) of energy flowed, but the sum of
the powers of the two constituents was only 1 J (average
1 W) in this interval. Where did the extra energy come from?
Was it borrowed from the future? It did not come from
the past since the generator was not yet on.

Just another example of why assigning too much reality
to the imputed powers of the components of superposition
is misleading.

Just another example of ignorance in action. Waves
possess energy that cannot be destroyed. Just because
you cannot track it doesn't mean it cannot be tracked.

That is why I pose the question, hoping for someone to
describe the mechanism that the energy for the flow that
is happening now can be borrowed from the future.

But what happens if the generator is turned off before
the future arrives? Where did the extra energy come from
then?

In other examples, you have suggested inserting a zero length
transmission line to aid analysis. Why not insert a zero length
transmission line with an impedance to produce the desired
reflection?

What would be the characteristic impedance of a length of
transmission that caused a reflection coefficient of 1.0?

Exactly. With the source impedance being zero, you can use
any impedance line you like.

No one has said there is zero energy. Only that there is
zero energy flow. For energy flow, one needs simultaneous
voltage and current.

Vfor/Ifor = Z0, Vfor*Ifor = Pfor = EforxHfor
If an EM wave exists, it is moving at the speed of
light and transferring energy. For Z0 purely resistive,
Vfor cannot exist without Vfor/Z0 = Ifor. Vfor is
always in phase with Ifor.

Assigning too much reality to component signals is
seriously misleading.

Assigning reality to the components of superposition
is seriously misleading???? Can we therefore throw
out the entire principle of superposition?

Well, you can solve these problems in other ways.
Superposition is not required, but it is certainly
convenient. I would not throw it out just because
the constituent powers do not necessarily have
any real meaning. I would just make sure I used
it in ways that did not mislead.

Until one can grasp the simplicity of a transmission line,
moving to the complexity of free space offers nothing but
obfuscation.

It is obvious that you have many things you desire to
hide inside that black transmission line to which we
are not even allowed to attach a directional wattmeter.

Since you are incapable of explaining what happens in
free space for all to see, why should we believe that
you have figured out what is happening inside a
transmission line where everything is hidden from view?

Actually, I have a pretty good grasp of what is happening
in free space, and it is all available to you by extension
from the behaviours of the one dimensional transmission
line. But there is little point in going there until the
transmission line is understood. Three dimensional free
space has much too much wiggle room. And you are an
expert at wiggling.

...Keith

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Keith Dysart wrote:
Actually, the transmission line input impedance is quite real,
formed from distributed capacitance and inductance. Like most two
terminal circuits, it can be reduced to simpler form.

I didn't say virtual impedances are not real. I
said they are not causes of anything and are,
instead, effects of superposition incapable of
causing anything in the complete absence of a
physical impedance.

You have for a long while now, confused cause
and effect. Maybe you should review the three
separate definitions of "impedance" given in
the IEEE Dictionary.
--
73, Cecil http://www.w5dxp.com

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On Apr 9, 9:33*pm, Cecil Moore wrote:
Keith Dysart wrote:
One thought experiment I rather like is the infinite SWR ideal line.
Cut the line at all the current zeroes. The voltage, current, and,
I'd suggest, the energy distribution do not change. The line can
be re-assembled, again with no change.

When you cut the line, you introduce an open circuit
where none existed before. Everything obeys the
distributed network model, at least conceptually.

Before you cut the line, there is no physical
impedance discontinuity and therefore no
reflections. You have to invent complete new
laws of physics for that one. I'm not against
you inventing new laws of physics but you need
to invent them before, not after, you use them. :-)

And yet....

The voltage distribution on the line, the current
distribution on the line and the energy distribution
on the line has not changed one iota.

This new physical impedance discontinuity has not
had any observable effect. All it seems to change
is the reflection of the unobservable forward and
reflected waves.

But the voltage distribution on the line, the current
distribution on the line and the energy distribution
on the line has not changed one iota.

These reflections can not be so important if they
can not be observed.

...Keith

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Keith Dysart wrote:
As long as you agree that the imputed energy in the
reflected wave is not dissipated in the source
resistor;

My ethical standards will not allow me to lie about
technical facts in evidence. You cannot bully me
into doing so.

When the average interference is zero, all of the
average reflected energy is dissipated in the source
resistor. It is true for all examples of Fig. 1-1.
You have not presented even one example where
that is not a true statement.

We should explore this new world.

There's no new world. All I am presenting is the
distributed network model which is lots older than
I. What you should present are your new laws of
physics that contradict the distributed network model.
--
73, Cecil http://www.w5dxp.com

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Roger Sparks wrote:
Of course one way would be if Vf actually did reflect from Vr.

That would require a brand new set of laws of physics.
--
73, Cecil http://www.w5dxp.com