Standing morphing to travelling waves, and other stupid notions
 

Keith Dysart wrote:
Expanding on statement 2...
Cecil's claim is that the "energy in" the
forward and reflected waves travel from end
to end on the transmission line.

The forward wave and reflected wave each possess
energy and momentum which must be conserved.
Assuming the transmission line is a homogeneous
medium, i.e. a constant Z0, there is nothing
anywhere along the line that can possibly cause a
reflection. A reflection is necessary to reverse
the momentum of a wave and reflections are impossible
in a homogeneous medium. By the process of elimination,
there must be something wrong with statement #1.

This is easy to demonstrate on the bench using a TV
signal. Even though there are points of zero power
in the standing wave, ghosting will be clearly visible
proving that the forward wave has made a round trip to
the end of the stub and back.

The superposition principle allows us to analyze the
forward wave and reflected wave separately. When we
do that, it is obvious that energy is flowing both
ways across that zero power node location and at all
other points on the line. If the reflected wave is
equal in magnitude to the forward wave, the net power
is zero at every point on the line, not just at the
nodes. The Poynting vector for the forward wave is
equal in magnitude and opposite in direction to the
Poynting vector for the reflected wave.
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:


3. The electric field is either 0 or 180 degrees apart from the
magnetic field. I proved that with math equations in an earlier
posting which I invited you to disprove and you declined. Hint:
see R&W quote below. The pure standing wave Poynting vector is
known to be zero. The only way for that to happen (when E and H
are both not zero) is for the E and H vectors to be mutually
parallel, i.e. 0 or 180 degrees apart.


Oops, I am afraid I must retract my previous congratulatory progress
report. You are obviously still confusing phasors with field vectors.
Until you get that terrible misconception sorted out, there is no hope
for further progress.

I assume that Hecht covers the equations and such. I am sure that Born
and Wolf cover this subject in detail. Check out page 277 in the 6th
edition or page 308 in the 7th edition. You will quickly observe that
the H-field is always perpendicular (90 degrees) to the E-field, even
for standing waves. There is no "0 or 180 degrees" involved.

Is there anything else you plan to teach me about physics? There is
still a whole lot I don't know. I think I may seek out another source,
however.

8-)

73,
Gene
W4SZ

Standing morphing to travelling waves, and other stupid notions
 

On 9 Jan, 19:27, Cecil Moore wrote:
On Jan 9, 3:13 pm, Jim Kelley wrote:

On what page has Dr. Hecht written "a standing wave is a different
kind of electromagnetic wave"?

Since I didn't say that Dr. Hecht said that, it must be a rhetorical
question. Here's what Dr. Hecht did say: In "Schaum`s College Physics
Outline" by Bueche & Hecht on page 214 is written: "Standing
Waves:....These might better not be called waves at all since they do
not transport energy and momentum." (Thanks to Richard Harrison for
that quote.) I agree with Dr. Hecht. Standing waves should not be
called waves at all since they do not meet the definition and
requirements for EM waves.

I asserted that expression for the sum of traveling waves and the
expression for the resulting standing wave pattern are related by trig
identity, as per page 140 of the 28th Edition of the CRC Standard
Mathematical Tables Handbook.

Sorry Jim, that's not what you said. You asked if I recognized the
trig identity that (presumably) equated a standing wave to a traveling
wave. If that was not your meaning, it is time to say exactly what
meaning I was supposed to assume.

The 'wave' which stands is merely an amplitude envelope for the waves
which move.

Key word there is "waves". A standing wave is NOT self sufficient - it
requires the superposition of a forward-traveling wave and a reverse-
traveling wave. A standing wave loses its EM wave identity in the
process of that superposition and apparently creates an illusion
capable of mass hysteria. To alleviate that hysteria, one has only to
compare the equations for standing waves and traveling waves or the
corresponding graphs of those functions to see that they are hardly
anything alike.
--
73, Cecil, w5dxp.com

Cecil'
How can one focus so long on travelling and standing waves when the
radiation portion
of the subject has not been explained? If waves is the subject it
cannot be discussed coherently if you cannot describe the mechanism of
radiation, and that subject is inexplicitely bound up with this whole
discussion. All of this is pure conjecture based on what is happening
behind a closed door which cannot continue until that door is opened.
Only then will this discussion be revealed for what it truely is,
which is all the things that could be happenning where the winner, if
there is one,will be picked when the door is finally opened. Until
then every thing is pure guess work.
Best regards
Art

Standing morphing to travelling waves, and other stupid notions
 

Gene Fuller wrote:
Oops, I am afraid I must retract my previous congratulatory progress
report. You are obviously still confusing phasors with field vectors.
Until you get that terrible misconception sorted out, there is no hope
for further progress.

Let's skip your objection for the moment and let you
answer this simple technical question.

Poynting vector = ExH = E*H*sin(A)

The Poynting vector for a pure standing wave = 0.

It is always zero even when both E and H are not zero.

So here is the question for you. Assuming that neither
E nor H is equal to zero:

When E*H*sin(A) = 0 (Poynting vector)

What are the possible magnitudes of angle 'A'?

This is a simple technical question having absolutely
nothing to do with confusing phasors with field vectors.

Please provide an answer.

I assume that Hecht covers the equations and such.

Yes he does. He also recognizes when the EH fields
incident upon a plane can be validly represented by
phasors. Apparently, Hecht also "confuses phasors
with field vectors". (SIC)
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

art wrote:
How can one focus so long on travelling and standing waves when the
radiation portion
of the subject has not been explained? If waves is the subject it
cannot be discussed coherently if you cannot describe the mechanism of
radiation, ...

The mechanism of radiation is pretty simple from a quantum
electrodynamic standpoint. Accelerated electrons emit
photons. Some of the photons escape the antenna. The
energy lost by the escaping photons must be replaced
by the source. QED. :-)

Art, if you would replace electrons with photons in
your blast-off theory, you will be closer to the facts.
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

Gene Fuller wrote:
Oops, I am afraid I must retract my previous congratulatory progress
report. You are obviously still confusing phasors with field vectors.
Until you get that terrible misconception sorted out, there is no hope
for further progress.

Draw a plane through which a plane EM wave is passing
normal to the plane. Now please explain exactly why
the E-field and H-field cannot be represented by
phasors.

I posted this separately to keep from confusing simple
issues with complex issues. Get it? Complex issues? :-)
--
73, Cecil http://www.w5dxp.com

Standing morphing to travelling waves, and other stupid notions
 

On 17 Jan, 09:51, Cecil Moore wrote:
art wrote:
How can one focus so long on travelling and standing waves when the
radiation portion
of the subject has not been explained? If waves is the subject it
cannot be discussed coherently if you cannot describe the mechanism of
radiation, ...

The mechanism of radiation is pretty simple from a quantum
electrodynamic standpoint. Accelerated electrons emit
photons. Some of the photons escape the antenna. The
energy lost by the escaping photons must be replaced
by the source. QED. :-)

Art, if you would replace electrons with photons in
your blast-off theory, you will be closer to the facts.
--
73, Cecil *http://www.w5dxp.com

Thank you for your civil reply.
What I am trying to say is that this long long thread has got a life
of its own that it is excluding a lot of people. If it concentrated on
say, a simple parallel circuit, a very simple circuit then the
absolute physics of what is being discussed would be an immense help
in explaining this wave discussion.ARRL states that an antenna is a
simple parallel circuit but this concentration on antenna workings is
blind siding every body as well as providing a means for twisting the
discussion because the makings of radiation is not known.
Why not illustrate waves in a simple parallel circuit so that
observers can partake in this discussion which, if it ever comes to
closure, could then be used to demonstrate their effect on radiation?
Onlookers are more than willing to partake in the discussion but
presently they are on the side lines because as presented it is
limited to only those whose intent is to argue without obtaining
closure and their feeding habits are insatiable as you are finding
out.
Best regards
Art Unwin KB9MZ......XG

Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:
Gene Fuller wrote:
Oops, I am afraid I must retract my previous congratulatory progress
report. You are obviously still confusing phasors with field vectors.
Until you get that terrible misconception sorted out, there is no hope
for further progress.

Let's skip your objection for the moment and let you
answer this simple technical question.

Poynting vector = ExH = E*H*sin(A)

Incorrect. The Poynting vector is defined as E x H*. The vector
directions are critically important. It is absolutely incorrect to try
to reduce to some scalar type equation. (The '*' means complex
conjugate, but this detail is not always important.)

The Poynting vector for a pure standing wave = 0.

Says who? Perhaps the time and space averages or "net", whatever that
means, but not the local instantaneous Poynting vector.


It is always zero even when both E and H are not zero.

Nonsense. It is E x H* at every point. If E or H is zero then the
Poynting vector is zero. Otherwise it will not be zero.


So here is the question for you. Assuming that neither
E nor H is equal to zero:

When E*H*sin(A) = 0 (Poynting vector)

What are the possible magnitudes of angle 'A'?

This is a simple technical question having absolutely
nothing to do with confusing phasors with field vectors.

Please provide an answer.

The answer is that you have started with incorrect equations.


I assume that Hecht covers the equations and such.

Yes he does. He also recognizes when the EH fields
incident upon a plane can be validly represented by
phasors. Apparently, Hecht also "confuses phasors
with field vectors". (SIC)

You have obviously misunderstood what Hecht is saying. A phasor does not
carry any vector information. It is a representation of magnitude and
phase angle only. That says absolutely nothing about the direction of
the field vector. The phase angle is completely unrelated to the vector
direction of the E-field and/or H-field.

73,
Gene
W4SZ

Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:
Gene Fuller wrote:
Oops, I am afraid I must retract my previous congratulatory progress
report. You are obviously still confusing phasors with field vectors.
Until you get that terrible misconception sorted out, there is no hope
for further progress.

Draw a plane through which a plane EM wave is passing
normal to the plane. Now please explain exactly why
the E-field and H-field cannot be represented by
phasors.

I posted this separately to keep from confusing simple
issues with complex issues. Get it? Complex issues? :-)

Cecil,

The phasor has nothing to do with spatial direction of the field vector.
It has everything to do with the amplitude and the (wt-kx) term in the
wave equation. (The 'x' is simply a distance measure in the propagation
direction. It does not say anything about the field vector directions,
since the fields are transverse to the propagation direction.)

This is really, really basic E&M stuff. If you still disagree, then you
are own your own.

73,
Gene
W4SZ

Standing morphing to travelling waves, and other stupid notions
 

art wrote:
Why not illustrate waves in a simple parallel circuit so that
observers can partake in this discussion which, if it ever comes to
closure, could then be used to demonstrate their effect on radiation?

This discussion, to a large extent, is concerned with the
nature of RF waves. There are no RF waves in a simple
parallel circuit. I posted a list of characteristics
of an EM plane wave. A parallel circuit doesn't match
those characteristics.
--
73, Cecil http://www.w5dxp.com