Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
 

Michael Coslo wrote:

...
Non sequitar here?

I do care about why and how the antenna works. I just don't agree with
AI4QJ's premise that Eznec is for discussion purposes only. It isn't, it
works just fine for design and implementation of them also.

Its a good tool for design of antennas. It gives me the data I need and
the expected outcome. I've designed simple antennas using "personal
level math" too. I don't do that much any more. I did the calculations
on paper too. I don't know if that makes them better than if they were
done using a calculator though.

There are some people that
operate at 27MHz who don't care how their radios work, only that they
can peg your meter at 10 pounds.

And there are some sanctimonius people out there who are educated
orders of magnitude beyond their intelligence, ready to throw out veiled
insults at the drop of a hat.......

Fortunately no one like that is in this conversation, eh?

- 73 de Mike N3LI -

I really don't want to be involved, the complexities of this argument
are too great a demand for my time, and I lack the deep understanding to
add beyond where others have already gone (indeed, they have gone well
beyond my understandings--I play a game of catch-up.)

However, I don't believe anyone is actually dismissing EZNEC. I know of
no better which does what EZNEC does. Nor am I aware of anyone actually
attacking the personalities behind or around EZNEC--it is the premises,
formulas, equations EZNEC is based on which harbors the discussion ...
and such discussion cannot hurt.

I believe the above is most accurate--just now and then a temper might
flare ...

Regards,
JS

Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
 

Cecil Moore wrote:
On Jan 9, 3:33 pm, Gene Fuller wrote:
When you get back to the wilds of Texas go check out some rural power
lines. Count the number of power factor correcting capacitors you see. I
bet it is a lot less than the equivalent of one per city block. Power
factor correcting capacitors are intended to correct for reactive loads,
such as motors, not for reflections or standing waves on open ended
power transmission lines.

Within the city limits of my home town of Madisonville, TX, there is
approximately one capacitor every city block. I had one in my front
yard. But the exact number and distances do not matter one iota. Those
capacitors exist to neutralize the inductive reactance in the system
at the load. I use exactly the same method to twist the feedpoint
impedance of my 75m Bugcatcher to 50 ohms.

You said: "Power factor correcting capacitors are intended to correct
for reactive loads,"

:-) Reactive loads cause reflections. The opposite reactance reduces
reflections. Does that scheme of matching a transmission line to a
load sound familiar? :-) My Bugcatcher antenna has about 25=j25 ohm
feedpoint impedance on 40m. I install a -j50 cap from antenna to
ground to achieve 50+j0 at the feedpoint. That's exactly what the
power company capacitors do.

Reflections *ARE* power factor problems. When the power company brings
the power factor to unity, they have eliminated reflections and turned
the system into a traveling wave energy delivery system. That you do
not recognize the similarity between VARS and standing waves is really
strange indeed. Standing waves contain nothing except VARS.
--
73, Cecil, w5dxp.com

You never give up, do you? Even when you are caught in an utter lie. You
know exactly what the capacitors are for, and it isn't to control
transmission line reflections from open ends of the line.

73,
Gene
W4SZ

Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:
On Jan 9, 3:30 pm, Gene Fuller wrote:
So do we now have a new requirement for waves and photons that there
must be *net* energy flow?

It's not a new requirement, Gene, just a very old requirement of
physics. Photonic, i.e. EM waves, do not flow back and forth as you
are implying. As long as the medium is homogeneous, i.e. doesn't
change, a photon travels at the speed of light in one direction in a
medium. So yes, net energy flow is absolutely a requirement for
photons.

EM waves *are* photons and do not vibrate back and forth in a medium.
They travel in one direction at the speed of light in the medium until
they encounter an impedance discontinuity. Virtually any physics book
with a diagram of the EM wave E-field and H-field will show the
direction of travel as one direction without the "one step forward and
one step back" concept that you are proposing.

You claimed that standing waves cannot be real waves because they cannot
obey photon rules. I easily demonstrated that idea is incorrect.v

All you demonstrated was your ignorance of the nature of photons. Your
analysis was incorrect. You are seeing the standing wave illusion and
assuming an impossibility of physics. It is very clear that you and
others simply do not understand the nature and physics of photons and
photonic waves.
--
73, Cecil, w5dxp.com

It is really amazing that you can make up so many requirements that are
completely unknown to the rest of the world. Is that a Mensa thing?

73,
Gene
W4SZ

Standing morphing to travelling waves, and other stupid notions
 

Richard Harrison wrote:
Jim Kelley, AC6XG wrote:
"On what page has Dr. Hecht written "A standing wave is a different kind
of electromagnetic wave?"

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."

I hope my question was not interpretted to imply that standing waves
transport energy and momentum.

Thanks for the page number.

73, ac6xg

Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
 

Gene Fuller wrote:

...
You never give up, do you? Even when you are caught in an utter lie. You
know exactly what the capacitors are for, and it isn't to control
transmission line reflections from open ends of the line.

73,
Gene
W4SZ

I do know it has been speculated that events on the sun have caused
"phenomenon" in utility lines to the point of power outages. Indeed, I
think there is still some mystery about why this occurs. And, I know
power companies have tried some fixes to these ... decades ago I had
line noise to the point I contacted the power company. They sent
someone out and, I thought, installed some sort of cap/filter on the
line--anyway, they did "stick something up there you could see." I did
notice a slight improvement--but finally ended up giving up the battle
with them ... a move to a quieter location changed everything.

Regards,
JS

Standing morphing to travelling waves, and other stupid notions
 

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.)

Hi Cecil - please note that Dr. Hecht does not post to this newsgroup.
If you follow this thread back, you will find that you were the one
who wrote "a standing wave is a different kind of electromagnetic wave".

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.

And so do I. But as I said, I am not disputing anything that Dr.
Hecht has written in his textbooks. Though, there are more elegantly
written physics books.

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.

See above.

ac6xg

Standing morphing to travelling waves. was r.r.a.a LaughRiot!!!
 

Hi Roy,

This helps a lot. I much better understand exactly how you are running the calculations.

I have just three comments/suggestions mixed into your posting.

On Wed, 09 Jan 2008 14:24:23 -0800
Roy Lewallen wrote:

Roger Sparks wrote:

Using the reflection point as the zero reference seems to correspond with an observation you made about the end of the line controlling the SWR.

The choice of zero reference is entirely arbitrary; any point on the
line, or off the line, for that matter, can be used. I used the input
end of the line as the x = 0 reference, so my equations are correct only
when that reference is used. The choice of a reference has no effect on
the SWR or any other aspect of line operation; it simply modifies the
equations.

For example, my equations for the first forward and first reflected
voltage wave we

vf1(t, x) = sin(wt - x)
vr1(t, x) = Gl * sin(wt + x)

and for the second set:

vf2(t, x) = Gs * sin(wt - x)
vr2(t, x) = Gs * Gl * sin(wt + x)

where here I've explicitly shown the source and load reflection
coefficients as Gs and Gl respectively. They were 0.5 and 1 in my second
analysis (the one with a 150 ohm resistor at the source).

The more general case where the line is some length L, rather than the
integral number of wavelengths in the example,

vf1(t, x) = sin(wt - x)
vr1(t, x) = Gl * sin(wt + x - 2L)

vf2(t, x) = Gs * Gl * sin(wt - x - 2L)
vr2(t, x) = Gs * Gl^2 * sin(wt + x - 4L)

Should we add an L to vf1(t, x, L) to keep the notation consistant in that we are considering 3 phase components. Rewriting,
vf1(t, x, L) = sin(wt - x + 0*L) (input point is congruent with refection point)
vr1(t, x, L) = Gl * sin(wt + x - 2L)(2L evaluates the entire line travel time)

In general,

(1) vfn(t, x) = (Gs * Gl)^n * sin(wt - x - 2nL)
(2) vrn(t, x) = Gl * (Gs * Gl)^n * sin(wt + x - (2n + 1)L)

where L is expressed in the same units as x and wt (degrees or radians).

These equations are correct with x being the distance from the input end
of the line.

I get your drift here. You are writting the general equation as if the first event is event zero, computer programming style.

Shouldn't these be written like this, changing the term "(2n + 1)L"?

(1) vfn(t, x) = (Gs * Gl)^n * sin(wt - x - 2nL)
(2) vrn(t, x) = Gl * (Gs * Gl)^n * sin(wt + x - 2(n+1)L)


You could, as I mentioned, use a different reference, for example x' = L
- x, where L is the line length in radians or degrees (same units as x
and wt). Then you have, simply by substituting L - x' for x:

vf1(t, x') = sin(wt - L + x')
vr1(t, x') = sin(wt + L - x' - 2L) = sin(wt - L - x')

and so forth, and for the general case,

(3) vfn(t, x') = (Gs * Gl)^n * sin(wt + x' - (2n + 1) * L)
(4) vrn(t, x') = (Gs * Gl)^n * sin(wt - x' - 2nL)

or, you can use x for the forward wave and x' for the reverse wave or
vice-versa in order to reference to the point the wave was reflected
from or where it will be reflected from. Any combination of the
equations is equally valid and will give correct results. You can't,
however, simply redefine the reference point without a corresponding
change in the equation. In general, equation 1 and equation 3 will give
different results if you put in the same value for x and x'; likewise
equations 2 and 4. There are some special cases, as you showed, where
you can change the reference without modifying the equations and not
have any impact on the sum of the waves. However, you can see from the
equations that this won't usually work.

Yes, the discussion becomes confusing quickly. If we were to have a rigorus discussion, we would need diagrams locating the points and directions. Lacking that, we are adrift.


The general case with complex reflection coefficients and arbitrary line
length is mathematically a little more difficult than the simple example
I worked earlier. Not only does each reflection have a different
amplitude than the previous one, it also has a different phase angle,
due to the line length and the reflection coefficients. Consequently,
the simple a / (1 - r) formula I used for summing the infinite series of
waves can't be applied to the equations in the form I used. This is
where a change to phasor notation is really beneficial, since the phase
delay simply becomes e raised to an imaginary exponent which can be
treated more conveniently than its constituent sine and cosine
functions. With phasor notation, the summing formula can be used even
for the general case to find the steady state results from the
individual reflected waves. There's a very excellent treatment of this
in Chipman's _Transmission Lines_ (Schaum's Outline Series). He does
just about exactly what I did in my earlier posting, except for the
general case and using phasors rather than time representations. It's an
excellent text and reference, and I highly recommend it for anyone
seriously interested in transmission lines.

Roy Lewallen, W7EL

This has been very productive for me Roy. I am gaining a much better appreciation for the whole subject, especially the use of phasors. Your use of the phase angle (posted with the corrections) was particularly helpful. I am planning to find Chipman's book.

Thanks for your efforts.

73, Roger, W7WKB

Standing morphing to travelling waves, and other stupid notions
 

On Jan 9, 11:22 pm, Roy Lewallen wrote:
Just what is a "wave", anyway? Are there different "kinds" of
electromagnetic wave?

Take a look at the E-field, H-field, and direction of travel for an EM
(photonic) wave. An RF standing wave does not behave like an EM wave
nor does it meet the definition of an EM wave which can be represented
by a Poynting vector. The Poynting vector for an RF standing wave has
a magnitude of zero and no direction.
--
73, Cecil, w5dxp.com

Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
 

Roger Sparks wrote:
Roy Lewallen wrote:
. . .
The more general case where the line is some length L, rather than the
integral number of wavelengths in the example,

vf1(t, x) = sin(wt - x)
vr1(t, x) = Gl * sin(wt + x - 2L)

vf2(t, x) = Gs * Gl * sin(wt - x - 2L)
vr2(t, x) = Gs * Gl^2 * sin(wt + x - 4L)

Should we add an L to vf1(t, x, L) to keep the notation consistant in that we are considering 3 phase components. Rewriting,

Yes, that's fine. It can be viewed as either a variable or a constant,
but it won't change during the course of a single analysis.

vf1(t, x, L) = sin(wt - x + 0*L) (input point is congruent with refection point)

It's not necessary to explicitly add the 0*L term, even if you consider
vf to be a function of a variable L. And it adds unnecessary clutter and
potential confusion without any effect on the result.

vr1(t, x, L) = Gl * sin(wt + x - 2L)(2L evaluates the entire line travel time)

The equation is correct and what I wrote. I don't understand the
parenthetical comment.

In general,

(1) vfn(t, x) = (Gs * Gl)^n * sin(wt - x - 2nL)
(2) vrn(t, x) = Gl * (Gs * Gl)^n * sin(wt + x - (2n + 1)L)

where L is expressed in the same units as x and wt (degrees or radians).

These equations are correct with x being the distance from the input end
of the line.

I get your drift here. You are writting the general equation as if the first event is event zero, computer programming style.

Sorry, I don't know what event you're talking about. And it's not
"computer programming style", but standard notation as you'll find in
any text. I am making the assumption that the line is initially
discharged, if that's what you mean.

Shouldn't these be written like this, changing the term "(2n + 1)L"?

(1) vfn(t, x) = (Gs * Gl)^n * sin(wt - x - 2nL)
(2) vrn(t, x) = Gl * (Gs * Gl)^n * sin(wt + x - 2(n+1)L)


You're right. I made an error -- thanks for spotting it. The reflected
wave has an additional 2L delay relative to the corresponding forward
wave, and I didn't write it correctly. I apologize for the error.

You could, as I mentioned, use a different reference, for example x' = L
- x, where L is the line length in radians or degrees (same units as x
and wt). Then you have, simply by substituting L - x' for x:

vf1(t, x') = sin(wt - L + x')
vr1(t, x') = sin(wt + L - x' - 2L) = sin(wt - L - x')

and so forth, and for the general case,

(3) vfn(t, x') = (Gs * Gl)^n * sin(wt + x' - (2n + 1) * L)
(4) vrn(t, x') = (Gs * Gl)^n * sin(wt - x' - 2nL)

Equation 3 has the same error.

or, you can use x for the forward wave and x' for the reverse wave or
vice-versa in order to reference to the point the wave was reflected
from or where it will be reflected from. Any combination of the
equations is equally valid and will give correct results. You can't,
however, simply redefine the reference point without a corresponding
change in the equation. In general, equation 1 and equation 3 will give
different results if you put in the same value for x and x'; likewise
equations 2 and 4. There are some special cases, as you showed, where
you can change the reference without modifying the equations and not
have any impact on the sum of the waves. However, you can see from the
equations that this won't usually work.

Yes, the discussion becomes confusing quickly. If we were to have a rigorus discussion, we would need diagrams locating the points and directions. Lacking that, we are adrift.

It depends on your ability to visualize equations, which usually
improves as you work with them. But sketches of the waves are definitely
very helpful in keeping track of what's going on. I hope my little
program will also prove helpful for this.

This has been very productive for me Roy. I am gaining a much better appreciation for the whole subject, especially the use of phasors. Your use of the phase angle (posted with the corrections) was particularly helpful. I am planning to find Chipman's book.

Thanks for your efforts.

You're welcome. I'm glad to help when I can. Chipman's book might be
hard to find, but it's well worth the search. I have more than a dozen
texts dealing with transmission lines, but Chipman's has material, like
the concise development of steady state from startup, that you'll find
in few others.

I haven't used phasors in these postings at all, but would have to in
order to sum the waves for the general case. In phasor notation,

vfn(t, x) = (Gs * Gl)^n * exp(j(-x - 2nL))
vrn(t, x) = Gl * (Gs * Gl)^n * exp(j(x - 2(n + 1)L))

where Gs and Gl are complex. So the ratio of successive terms vfn(t, x)
/ vfn-1(t, x) = vrn(t, x) / vrn-1(t, x) is a multiplier term Gs * Gl *
exp(-j2nL). So we can use the formula for summing an infinite series to get

vf(ss)(t, x) = vf1 / (1 - Gs * Gl * exp(-j2nL))
vr(ss)(t, x) = vr1 / (1 - Gs * Gl * exp(-j2nL))

which can be evaluated as complex numbers and converted back to time
functions for evaluation. While the summation of the infinite series
could almost certainly be done by clever application of trig identities,
it's trivial with phasors.

Roy Lewallen, W7EL

Standing morphing to travelling waves, and other stupid notions
 

Cecil Moore wrote:

An RF standing wave does not behave like an EM wave
nor does it meet the definition of an EM wave which can be represented
by a Poynting vector. The Poynting vector for an RF standing wave has
a magnitude of zero and no direction.

So much for the Poynting vector of a position envelope. What are your
thoughts regarding the Poynting vector for a time varying envelope of
an electromagnetic wave? :-)

ac6xg