On Jun 6, 10:13*pm, lu6etj wrote:
On 6 jun, 18:00, Keith Dysart wrote:
On Jun 6, 9:45*am, Cecil Moore wrote:
On Jun 5, 6:28*pm, Keith Dysart wrote:
There are indeed negative values. These occur when the energy is
flowing in the other direction, ...

Let's take a close look at the illusion that you are seeing and not
comprehending. Observe a snapshot of the instantaneous power envelope
of a traveling wave. It is a sinusoidal envelope with peak
instantaneous power levels and zero instantaneous power levels. When
it is traveling in the forward direction we consider that to be
positive power. When it is traveling in the reverse direction, we
consider that to be negative power. It is only a directional
*convention* not proof that negative power exists. The only waves that
can exist as waves on a transmission line are traveling waves.

Ahhh. I see part of your problem. You are thinking envelopes.

You need to change your point of view to be a particular point on the
line.
At this point, there is a function that describes the voltage: V(t).
It
may or may not be a sinusoid. There is a function for the current:
I(t).
And from these can trivialy be derived a function for power:
P(t)=V(t)I(t).

When I clip my instantaneous voltmeter across a line and measure 0 for
all time, I can confidently say that no energy is flowing, for there
is
not. I am curious as to what you would answer?

In "Optics", Hecht says instantaneous power is "of limited utility."
You seem to have discovered that limit, stepped over it, and stepped
in it. :-)

Well, Hecht may have his limitations when dealing with Optics, but
there
is no reason to expect these same limitations to apply to circuit
analysis.

...Keith

Hi folks, good night (from here).

I do not disagree with anything you have written, but I do think it
is much too early to introduce Poynting vectors and lossy conductors
to the discussion.

Hello Keith, Yes, I understand your comment, I introduced Poynting
vector only because both, energy and power, are scalars and we can not
talk about scalars having direction without get in conceptual
troubles; flux of power instead, have direction because surface vector
presence in its definition gives directive characteristics to power
crossing an imaginary surface.
Slanted flux of electromagnetic power (Poynting) due resistive
conductor simply seems to me a good example of a power flux in a TL
not totally coincident with axial direction to provide a little more
supporting to "directive" notion of Power Flux.
However IMHO power flux do not seems to me more complicated than
power, work, voltage, potential, energy, E and H fields, etc. All of
them -I believe- are not very simple stuff :(, but they are very
funny and interesting, indeed...!! :D. What do you think?

My interests lie in understanding the behaviour of transmission lines
to a level necessary to predict their basic behaviour. I did not find
that I needed power flux to achieve this so I have not explored it. I
suspect that you are right and it is an interesting topic.

.....
Please would you mind tell me why "sine wave" it is not a correct use
of "wave" word. The only dictionary I have = "Oxford *advanced
english dictionary of current english defines wave as: "move to and
fro, up and down", I believe also in english there are word qualifiers
(sine, traveling, standing, etc) who specify the precise meaning of
them in diverse contexts. Am I wrong about this?.

Sine wave. Square wave. Triangle wave. Sawtooth wave. Waveform.
Waveshape. 'Wave' seems to fit well with many words. I do not see a
problem.

....
Sorry by my insistence about convenience of discuss about "models".
Please let me bring a citation:
"At times, two quite differents models may serve equally well, but
eventually one is usually found to prevail, not because it is right,
but because it is both more convenient and more logically constructed.
After all, models are constructed for convenience in thinking and
recording, not as photographic images of nature"
(From "Electromagnetic Engineering", Ronold W.P. King (PhD), page 94.
McGraw Hill.1946).

It seems to me that all is well as long as the model is used properly
in the contexts in which it yields answers which are adequately
accurate.

....
I studied "Principle of Conjugates Impedance Matching" in my early
student days and the "mirror reflection" explained by Walter Maxwell
in his article agree with my undestanding about "where the reflected
waves go" because to balance magnitudes it is necessary that they
found a full mismatch on its way (path?) to generator. My own limited
analisis led me to the same notion even without conjugate match if I
calculate Incident and reflected voltages values in a half wave TL (as
my early thread example),
As I said, reading Cecil's web page quarter wave line examples led me
to considerate another possible representations of the problem, in
addition Owen's own ideas about it also made me consider the issue
from another point of view.

When I was trying to understand the behaviour of reflections in
transmission lines, I found it extremely valuable to consider
waveforms
other than sinusoids. Step functions into open, shorted and properly
terminated lines were quite enlightening. The arithmetic is much
easier to perform than for sine waves and some of the results rather
surprising.

For example, apply a step function from a matched generator to an
open transmission line. After the step makes one round trip, there
will be a constant voltage everywhere on the line and the current
will be zero everywhere. The wave reflection will show that there
is a constant forward wave which is summed with a constant reflected
wave to produce the constant voltage on the line. This is a strong
example of why there is not necessarily power in the forward and
reflected wave.

Other interesting thought experiments are pulses and pulse trains.
Arrange the timing so that a forward pulse collides with a reflected
in the middle of the line. What are the voltages and currents that
would be observed? Try alternating positive and negative pulses.

And lastly, inject signals simultaneously from both ends of a
transmission line. What is the result?

When doing these, I would compute the power provided by the source
and dissipated in the source resistor (I tend towards ideal
Thevenin generators to simplify the analysis, though it is
worth occasionaly doing the same with Norton), the energy stored
in the line and the energy being dissipated in the load resistor,
if there is one. Dealing with all of this in the time domain can
help make the energy flows clear.

These simple thought experiments definitely helped my understanding.
Some of the assertions that have been made can be shown to be false
when tested with these waveforms and analysis.

....Keith

On Jun 6, 3:40*pm, Keith Dysart wrote:
In the past you have insisted that only average powers were relevent.
Does this mean you are ready to look at power (i.e. energy flow) in
the time domain?

Your concepts violate the laws of physics so no, I am not going to
discuss it with you until you correct your numerous technical
blunders. You need to give up on waves that violate Maxwell's
equations. You need to give up on the occurrence of reflections where
reflections are impossible. You need to give up on the concept that
photons obey your every whim.
--
73, Cecil, w5dxp.com

On Jun 6, 3:48*pm, Keith Dysart wrote:
You do seem to mention looking in the mirror quite frequently, as if
it had something to do with understanding the behaviour of a
transmission line.

Are you aware that visible light and RF waves are identical phenomena,
just at different frequencies? An RF transmission lines operates much
the same as fiber optics.

When I clip my instantaneous voltmeter across a line and measure
0 for all time, I can confidently say that no energy is flowing, for
there is not. I am curious as to what you would answer?

I have already answered. I agree with you that there is no NET energy
flowing across that boundary. All it means is that the forward
Poynting vector and reverse Poynting vector are of equal magnitudes.
The reflection coefficient at that zero voltage point is zero so
reflections are impossible. Yet, your concept requires a reflection at
every node - which violates the laws of physics. Until you eliminate
those magical metaphysical functions from your concepts, they are "of
limited utility", to quote Hecht.

Again, you are saying that there is zero traffic on the Golden Gate
Bridge because the northbound vehicles equal the southbound vehicles.
There is zero NET traffic, but such information is worthless. Someone
still has to repair the bridge.
--
73, Cecil, w5dxp.com

On Jun 6, 9:13*pm, lu6etj wrote:
I studied "Principle of Conjugates Impedance Matching" in my early
student days and the "mirror reflection" explained by Walter Maxwell
in his article agree with my undestanding about "where the reflected
waves go" because to balance magnitudes it is necessary that they
found a full mismatch on its way (path?) to generator. My own limited
analisis led me to the same notion even without conjugate match if I
calculate Incident and reflected voltages values in a half wave TL (as
my early thread example),
As I said, reading Cecil's web page quarter wave line examples led me
to considerate another possible representations of the problem, in
addition Owen's own ideas about it also made me consider the issue
from another point of view.

Miguel, you might be surprised to know that I got the constructive/
destructive interference concepts first from Walter Maxwell's,
"Reflections". Take a look at "Sec 4.3 Reflection Mechanics of Stub
Matching". Walt says:

"The destructive wave interference between these two complementary
waves at the stub point causes a complete cancellation of energy flow
in the direction toward the generator."

"Conversely, the constructive wave interference produces an energy
maximum in the direction toward the load, resulting from the sum of
the two reflected waves and the source wave."

Walt clearly understands that wave cancellation, interference, and
redistribution of reflected energy back toward the load is involved
with his "conjugate mirror" and virtual-short-circuit concepts.

So you see the concept of wave cancellation of complimentary reflected
waves at a Z0-match didn't come first from me. The concept of all of
that energy involved in wave cancellation changing direction and
joining the forward wave didn't come first from me. I only resorted to
the field of optics to gain additional technical information and
expanded on Walt's original "Reflections" concepts in my article.
--
73, Cecil, w5dxp.com

Keith Dysart wrote:

These simple thought experiments definitely helped my understanding.
Some of the assertions that have been made can be shown to be false
when tested with these waveforms and analysis.

...Keith


Here is a thought experiment for you.


A C E
+----\/\/\--+--/\/\/\--+--/\/\/\--+--/\/\/\--+
| |
--- -
- ---
| B | D | F |
+-----------+-----||---+---||-----+----------+
| |

Four resistors, equal value.
Four DC sources, equal value.
Voltage A-B = 0, no power past here.
Voltage C-D = 0, no power past here.
Voltage E-F = 0, no power past here.

No power crossing the boundaries on either side of the resistor between
A and C. The resistor is not directly connected to a supply, how is it
dissipating power, if any?

(Yes, I do know the answer.)

On Jun 7, 10:11*pm, Cecil Moore wrote:
On Jun 6, 3:40*pm, Keith Dysart wrote:

In the past you have insisted that only average powers were relevent.
Does this mean you are ready to look at power (i.e. energy flow) in
the time domain?

Your concepts violate the laws of physics so no, I am not going to
discuss it with you until you correct your numerous technical
blunders. You need to give up on waves that violate Maxwell's
equations. You need to give up on the occurrence of reflections where
reflections are impossible. You need to give up on the concept that
photons obey your every whim.
--
73, Cecil, w5dxp.com

It took a lot of words to say "no, I am not ready."

It is too bad, because the time domain is quite enlightening.

....Keith

On Jun 8, 5:30*am, joe wrote:
Here is a thought experiment for you.

Does anyone know of a better Google solution to reading an ASCII
schematic than copying from Google and pasting to Notepad?
--
73, Cecil, w5dxp.com

On Jun 8, 6:04*am, Keith Dysart wrote:
It is too bad, because the time domain is quite enlightening.

Nothing wrong with a time domain analysis but analyzing problems whose
basic premises violate the laws of physics is a waste of my time and
yours.
--
73, Cecil, w5dxp.com

On 8 jun, 09:54, Cecil Moore wrote:
On Jun 8, 6:04*am, Keith Dysart wrote:

It is too bad, because the time domain is quite enlightening.

Nothing wrong with a time domain analysis but analyzing problems whose
basic premises violate the laws of physics is a waste of my time and
yours.
--
73, Cecil, w5dxp.com

Good day. Sorry for the large extension of this post, my friends...

My interests lie in understanding the behaviour of transmission lines
to a level necessary to predict their basic behaviour. I did not find
that I needed power flux to achieve this so I have not explored it. I
suspect that you are right and it is an interesting topic.

OK. I understand. I suposse you are more interested in "know how".
When I complained about "the bench" at Richard, I was thinking on so
many "know how" working years in my life. Today, I have more time to
the "know WHYs" and I am trying to take my chance... :)
A knowledge on Smith Chart (or software equivalent tools) using, solve
most (if not all) of our ham practical and professional situations and
provide enough basic theory for design purposes, I think in such sense
I agree with you about it; however seems to me this topic thread have
dealt a little more in the why's than the how's :)

Look, several years ago many hams in my country -Argentine- came from
technical schools, I become a ham in my seventeens (1969) when I was a
very young electronic technician student. Here we have three
fundamental educative levels: Primary, secondary (college?) and
terciary (university). In secondary and terciary levels one of the
first matters we study is physics. If we study electronics -on RF
speciality-, only when we reach later study years of each level we
learn transmission lines in the frequency domain with infinite
lattices of RLCG, Telegrafer's equations solution, Smith charts,
impedances, reactances, etc.
If you do not go to study any RF especialities, the only knowledge you
will have about transmission lines will be the physics ones. Physics
models teach us the associated phenomena reffering basically to
electromagnetic fields = we learn about, E field, H field, power and
energy in more basics terms that frequency domain later more advanced
studies. We do not learn typical AC models in basic physics (as you
can see in Resnick-Hallyday books, for example, I can not give you
college's references books because I study from local authors).
In addition at very early physical mechanics courses we learn
stationary and traveling waves, superposition principle and late,
interference, in optics.
Probably this is not the way to approaching to this topic that medium
Ham employ because our natural ansiety to put the rig to work :D but
seems to be a consensus about what is more basic and what more complex
in formal pedagogic/understanding approaches to this matters.

May be for that some of us tend to emphasize in directional power flux
and other similar "ugly stuff" to analize transmission line questions,
Perhaps for this reason it is easy and illustrative to me the Cecil's
bridge car analogy about net energy flux, in addition, energy fluxes
crossing areas results very intuitive to me because I can easily
visualize (imagine) thousands of them hit and cross my body all the
time. Sun light and infrared energy flux, light in houses, streets
lights, sky diffused light, RF waves from broadcast and Hams, cellular
phones, etc. Instead it is not so ease visualize in such intuitive
context a single point with a permanent zero voltage (or E field,
better) all the time.

Measurement of interference phenomenom requires much more sofisticated
and special reductive technics to simplify the problem. One of this
technics it is, for example, voltage measurement on a transmission
line point with a zero volt pure AC voltage node; but as Cecil et al
said, a zero voltage point does not implicate not power flux crossing
that point, that is a very known wave interference phenomenom, it is a
little easy to visualize it if we remember that fields are "force
fields" -fields are forces acting on testing devices- (charges,
compass needles, etc), as we learnt in Coulomb laws. Fields being
forces let us intuite that having two horses pulling a rock in right
angles results in rock moving on a direction resulting of composition
of that forces. Seem to be only one force acting in movement direction
but are two!. also you can have both horses pulling in opposite
directions, then we do not measure any movement and we could think
there is not any force acting on the rock!, but our zero force
measurement do not implicate there are not two horse pulling the
rock! , zero net force it is different of zero force, I think we agree
in that.

I believe I undestand your reasoning: P=V*I, = not V, not P!, it is
OK. But power not represent the internal system energy, power
implicate "energy developed = work/time", you need energy (applied
during certain time, then "power") to accelerate a charge, but the
charge can have cinetic energy of its own; then, zero volt line point
simply are a point where not any energy it is ADDED to the charges.
not a point where there is not have (or not can have) preexistent
electric energy (current) flowing; why zero volt net force field point
would be stop travelling wave energy flow?; think of zero volt line
point as a zero potential energy point, not acceleration in it, as the
lowest part of a roller coaster...
Incidentally, Poynting vector is defined as "speed of energy flux by
unity of area", it is a different thing that power developed on
interchange of energy phenomena such electric energy converted to heat
or chemical reaction or movement, if we remember what we learn about
P=V*I in Joule law (electric to heat transformation) it is a little
more evident its transforming (not transport) energy context. Thus,
transmited power its different than "developed power" in the other
sense (perhaps here my translation not be clear enough). What is your
opinion?

Miguel Ghezzi LU6ETJ

PS: I have some more things in my inkwell about models used on our
issue but I have to leave it for future postings :)

On Jun 8, 4:20*pm, lu6etj wrote:
I believe I undestand your reasoning: P=V*I, = not V, not P!, it is
OK. But power not represent the internal system energy, power
implicate "energy developed = work/time", you need energy (applied
during certain time, then "power") to accelerate a charge, ...

One comment here. "Power" is defined differently in pure physics vs
engineering. In physics, power requires work to be done. In
engineering, one definition of power is energy passing a point in a
unit of time, i.e. the energy doesn't have to be used up to be defined
as power. One might think of it as potential power waiting to be used.
These two quite different definitions of "power" are at the root of a
lot of disagreements.

For RF engineers we should probably honor "The IEEE Dictionary"
definition: "power - the rate of generating, transferring, or using
energy". Since energy cannot be destroyed, all energy that has been
generated and is so far unused, is in the process of being
transferred. Thus any reflected energy in a transmission line that is
in the process of being transferred will be used (lost to heat or
radiated) during the transient state following key-up.
--
73, Cecil, w5dxp.com