On Apr 16, 12:19 pm, Richard Clark wrote:
On 16 Apr 2007 10:07:55 -0700, "K7ITM" wrote:

I have yet to see Cecil, or anyone else, post an example of how waves
can become perfectly collinear, except at an interface: a
discontinuity in a transmission line, a partially-reflecting surface
in an interferometer, ... -- a physical interface of some sort.

Two sources impinging upon each other? If we take a specialized
example of lasers, their being bore sight in opposition. If we take
two antennas, where their -ahem- waves meet, again in opposition.
Nothing physical but the sources are required. As for perfection....

Best stick with transmission lines, and not lasers, but yes, you're
absolutely right. In my mind I was qualifying it as being waves
propagating in the same direction, since the discussion centers around
propagating EM cancelling out in a finite (non-zero) volume, and as
far as I know, there hasn't been anyone suggesting that waves on a
line in opposite directions cancel over a non-zero distance. I should
have explicitly stated that qualification, especially in this group.
I should, of course, also specified that all this propagation is
assumed to be in a perfectly linear medium, so someone can now offer a
transmission line made from wire wound around a ferrite core, shunted
by varicap diodes, and we'll have a nice nonlinear TEM line that all
sorts of strange things can happen on.

I have yet to see Cecil, or anyone else, post an example of perfectly
collinear waves that perfectly cancel over some small finite volume
which do not also cancel perfectly at all points up to their point of
origin: a physical interface. In other words, lacking that example,
I see NO physical evidence that those waves exist beyond that "point
of origin." Specifically, I have not seen an example of a uniform TEM
line on which it is supposed that two waves cancel perfectly over some
distance, but over some other length on the same line with no
interposed interfaces, the two do not perfectly cancel.

This one is extremely simple to reveal. Those familiar with
microwaves would immediately sputter "Magic T!" Tom, if you have not
seen this offered in several many posts by me, it stands to reason you
must have filters set (but how is it you are reading this?). Of
course, this like the "rat race" coupler (or hybrid ring) all share
the same dynamics. However, for the "Magic T" the cancellation port
is fed by two apparent sources wherein their phases combine to a null
(given the appropriate phases, of course) at this "point of origin."
This may beg what is meant by interface as the "Magic T" is replete in
transmission line arms - however, all are identical in characteristic
Z (a uniformity), all can be Zload matched (a uniformity which then
discards the useful illustration of cancellation), and all are TEM (a
uniformity). As for perfection....

The "Magic T" as I know it is most certainly a physical interface in
the line. It's a four-port network. I'm surprised you'd even think
to mention it as a counter-example. Next you'll be saying that a
Michaelson interferometer (also a 4-port, where one port is commonly
terminated in a full reflection) isn't a physical interface...


I have yet to see Cecil, or anyone else, post an example wherein the
behaviour of a uniform, linear TEM transmission line is not adequately
explained by the propagation constant of the line, the concept that Vf/
If=-Vr/Ir=Zo, Vtotal=Vf+Vr, and Itotal=If+Ir, and the boundary
conditions at any transitions or interfaces.

Hmmm, those filters must have been a brick wall: In times past I've
offered Soliton waves in fiber optics (TEM lines, of course) wherein
there is no dispersion as would be typically found. This, of course,
stretches the concept of "linear" TEM lines insofar as NONE are! So
much for perfection, or practicality....

Fiber optics are TEM lines??? I find lots of references to the
contrary. Can you give me any showing that they are?

I have to admit I haven't paid any attention to anything you've posted
about Soliton waves. (Do they differe from soliton waves?) Are you
saying they propagate as TEM waves in a linear medium but don't follow
the same rules with respect to linearity that other TEM waves do? Do
they not behave at boundaries in the same way that other waves do?
How do you create one in a piece of coax? I'm afraid I don't see in
what way they might be an example of something that propagates as a
TEM wave but doesn't obey the rules I'm used to seeing TEM waves obey.


Whether or not any claims about power and energy formulas are accurate
or not, I don't know. I'd have to be convinced they're actually
useful before I looked at them more closely. So far, I've not been
convinced of their utility. But then maybe I'm just slow. I could
never see how the current at two ends of a wire (with no other
conductive paths between the ends) could be different unless the wire
in between was storing or giving up charge, either, and I was LAUGHED
AT and told that was just flat-out wrong. The laughing didn't seem to
help; I still don't see it.

I don't trust claims, and measurements proving them even less so. If
this statement above is about perfection; then, again, the last word
has yet to be made such that accuracy can be guaranteed. [Even Ohm's
law isn't accurate. Hence any power statement made in regard to it
fails at some digit to the right of the decimal.]

No, it's about practicality. Convince me that calculations based
primarily on power (or energy) rather than on voltage and current
offer me something useful, with respect to TEM lines, and I might have
a closer look at them. I have tools that give me an accurate picture
of the distribution of voltage and current on a line as a function of
time, at any point along the line. From these, I can find the power
delivered to loads (a useful, practical quantity that I do care
about). I can calculate the power dissipated as heat as a function of
distance along the line, which in some cases is useful and practical
information. I can easily calculate the steady-state load impedance
presented to a source, given a particular line and load, and again
that's useful, practical information. Give me a practical reason for
caring about "power" in "forward" and "reverse" waves on a TEM line.

When I brought up that applet a few days ago, the same thing jumped
out at me, and gave ME a good laugh. Yes, it shows waves cancelling,
but it never shows how they got there.

When a sudden galactic Gamma burst hit us in the past, it too was of
unknown origin (meaning no one knew how they got here). Later, we put
up satellites to warn detectors an event was coming so we could
roughly triangulate any new Gamma burst. One such event suggested a
galactic black hole. Back of the envelope calculations have suggested
similar Gamma burst sources (millions of light years away, but bore
sight on us) could obliterate life in an entire solar systems in the
space of milliseconds. Some might call that canceling waves - or a
cosmic laugh.

I don't know what that was all about, but it doesn't matter anyway,
since I'm only a figment of Cecil's imagination.

Cheers,
Tom


OK, so admittedly all responses above entail exotic, rare, or strained
examples. Some are ordinary within the context of experience. If all
of your provisos were combined, then yes, nothing would satisify by
virtue of a self-fulfilling definition.

Copy made in accordance with "Fair Use."

73's
Richard Clark, KB7QHC

On 16 Apr 2007 14:29:01 -0700, "K7ITM" wrote:

In my mind I was qualifying it as being waves
propagating in the same direction, since the discussion centers around
propagating EM cancelling out in a finite (non-zero) volume, and as
far as I know, there hasn't been anyone suggesting that waves on a
line in opposite directions cancel over a non-zero distance.

Hi Tom,

Then the challenge devolves to a self-fulfilling proposition (which
may be your point at this turn) as it requires two sources to occupy
the same point.

The "Magic T" as I know it is most certainly a physical interface in
the line. It's a four-port network. I'm surprised you'd even think
to mention it as a counter-example. Next you'll be saying that a
Michaelson interferometer (also a 4-port, where one port is commonly
terminated in a full reflection) isn't a physical interface...

Again, you have a self-fulfilling proposition. This has nothing to do
with obtaining a condition of interference, but about filling an
impossible constraint.

Consider, you do not mention where the line begins (or ends) or
otherwise constrain this physically, and yet you can easily dismiss an
example out of hand. It seems it is up to the respondent to feel out
these constraints, much like reading Braille on a waffle iron.

Any issue of "interface" as has been offered by quotes from Terman, or
otherwise bandied about in discussion is that the "interface" presents
a disturbance (a step-wise shift in characteristic Z). There is
nothing, per se, about an interface that disqualifies it from the
study of interference as it is quite obvious power must enter through
a system through some interface.

The "Magic T" and similar devices make every effort to present a
non-perturbing environment to the transmission of waves, otherwise
their utility would be nil.

Also, the "Magic T" offers an excellent solution to your first issue
in that it does present two sources combining at one point whereby
there is total null following. There is absolutely nothing about the
"Magic T" that disturbs the field with discontinuities and would
appear (from the perspective of the energy) as continuous.

Fiber optics are TEM lines??? I find lots of references to the
contrary. Can you give me any showing that they are?

I have to admit I haven't paid any attention to anything you've posted
about Soliton waves. (Do they differe from soliton waves?) Are you
saying they propagate as TEM waves in a linear medium but don't follow
the same rules with respect to linearity that other TEM waves do? Do
they not behave at boundaries in the same way that other waves do?

OK, this is foreign turf for you. I don't think offering a course on
Solitons, fiber optics and TEM waves will change the discussion here.
You asked for examples and they were provided. Do you want to further
constrain to RF below a certain frequency?

How do you create one in a piece of coax? I'm afraid I don't see in
what way they might be an example of something that propagates as a
TEM wave but doesn't obey the rules I'm used to seeing TEM waves obey.

So we are now confined to coax? The refinement of constraints is
painting examples into a corner as we progress.

I don't trust claims, and measurements proving them even less so. If
this statement above is about perfection; then, again, the last word
has yet to be made such that accuracy can be guaranteed. [Even Ohm's
law isn't accurate. Hence any power statement made in regard to it
fails at some digit to the right of the decimal.]

No, it's about practicality.

Practicality when your post is littered with "perfect?" You have
rebutted every practical example offered! Do we now constrain what
practical means or is this about studying the effects of interference?

Convince me that calculations based
primarily on power (or energy) rather than on voltage and current
offer me something useful, with respect to TEM lines, and I might have
a closer look at them.

I presume this challenge is to the general readership.

73's
Richard Clark, KB7QHC

On Apr 16, 3:38 pm, Richard Clark wrote:
On 16 Apr 2007 14:29:01 -0700, "K7ITM" wrote:

In my mind I was qualifying it as being waves
propagating in the same direction, since the discussion centers around
propagating EM cancelling out in a finite (non-zero) volume, and as
far as I know, there hasn't been anyone suggesting that waves on a
line in opposite directions cancel over a non-zero distance.

Hi Tom,

Then the challenge devolves to a self-fulfilling proposition (which
may be your point at this turn) as it requires two sources to occupy
the same point.

Well, maybe I'm mistaken, but I was under the impression that there
was someone around here who was promoting the idea that two waves
propagating in a linear medium could cancel over some non-zero finite
volume, but not cancel everywhere along their path, even though that
path was uninterrupted by any discontinuities in the medium. Maybe
I'm mistaken, but I was under the impression that there was someone
around here who was promoting the idea that calculations based on
power rather than on voltage and current in a TEM transmission line
offered some inherent value. I posted my original, "I have yet to
see...," statements as a way of saying that I'm not convinced about
the truth of either of those ideas, and it would go a long ways toward
convincing me if someone posted examples. I'm still waiting. I still
don't have a reference that a fiber optic cable is a TEM transmission
line, though I have others that say that it's not. I still don't have
information on whether a soliton wave can propagate in a linear
medium, though I have references that say it is a non-linear
phenomenon that occurs in non-linear media. If you can convince me
that a wavefront coming to a Magic T doesn't see it as an impedance
discontinuity, we could perhaps post more about that--or not.

But so far, your responses make me think you don't disagree with my
implicit suggestions: that it's impossible to distinguish between the
condition of two cancelled waves that somehow still exist (huh?) and
the condition of no wave at all; and that there's precious little
value in doing calculations based on "forward power" and "reverse
power" in TEM lines--qualify that if you want by limiting it to the
frequency range where we find it relatively easy to express what's
going on in terms of voltage and current. That seems a reasonable
qualification in this newsgroup.

Beyond that, you're of course welcome to go off on whatever tangents
you wish. Basenote drift is the expected norm here; I engage in it
all the time myself.

And I still don't exist; I'm only a figment of Cecil's imagination.

Cheers,
Tom

K7ITM wrote:
Well, maybe I'm mistaken, but I was under the impression that there
was someone around here who was promoting the idea that two waves
propagating in a linear medium could cancel over some non-zero finite
volume, but not cancel everywhere along their path, even though that
path was uninterrupted by any discontinuities in the medium.

Would you please name the person who said such. It certainly
was NOT me. The waves involved in the cancellation are
canceled so fast that they cannot be viewed on an o'scope.
But if they didn't exist, nothing would happen at an
impedance discontinuity.

Take the s-parameter equation, for instance.

b1 = s11(a1) + s12(a2) = 0

If s11(a1) doesn't exist, then s11 and/or a1 must not exist
either. But s11 and a1 can be measured. So if s11 and a1
exist, does s11(a1) exist only to be canceled or did it
never exist. If s11(a1) never existed, what the heck is
an s-parameter analysis good for?

Maybe
I'm mistaken, but I was under the impression that there was someone
around here who was promoting the idea that calculations based on
power rather than on voltage and current in a TEM transmission line
offered some inherent value.

An energy analysis is not supposed to replace a voltage analysis
but is supposed simply to settle the question, Where does the
energy go? If we assume that in a Z0 transmission line, that
Vfor^2/Z0 = forward joules/sec and Vref^2/Z0 = reflected joules/sec,
the energy analysis falls out from the voltage analysis.

If you don't care where the energy goes, that's cool, but some
of us, like Bruene and Maxwell, do care and have been arguing
about it for decades.

To keep an energy analysis from falling out from the voltage
analysis, we have been told that reflected waves don't exist,
and if they did exist, they would be devoid of energy content.
"I have yet to see" an EM wave that can exist devoid of
energy content.
--
73, Cecil http://www.w5dxp.com

On 16 Apr 2007 17:50:10 -0700, "K7ITM" wrote:

On Apr 16, 3:38 pm, Richard Clark wrote:
On 16 Apr 2007 14:29:01 -0700, "K7ITM" wrote:

In my mind I was qualifying it as being waves
propagating in the same direction, since the discussion centers around
propagating EM cancelling out in a finite (non-zero) volume, and as
far as I know, there hasn't been anyone suggesting that waves on a
line in opposite directions cancel over a non-zero distance.

Hi Tom,

Then the challenge devolves to a self-fulfilling proposition (which
may be your point at this turn) as it requires two sources to occupy
the same point.

Well, maybe I'm mistaken, but I was under the impression that there
was someone around here who was promoting the idea that two waves
propagating in a linear medium could cancel over some non-zero finite
volume, but not cancel everywhere along their path, even though that
path was uninterrupted by any discontinuities in the medium.

Hi Tom,

'T'warn't me.

Maybe
I'm mistaken, but I was under the impression that there was someone
around here who was promoting the idea that calculations based on
power rather than on voltage and current in a TEM transmission line
offered some inherent value.

'T'warn't me.

I posted my original, "I have yet to
see...," statements as a way of saying that I'm not convinced about
the truth of either of those ideas, and it would go a long ways toward
convincing me if someone posted examples. I'm still waiting.

'T'was me.

I still
don't have a reference that a fiber optic cable is a TEM transmission
line, though I have others that say that it's not.

That example of the non-TEM fiber optic would be rare species indeed.
I've seen them, but that hardly constitutes the sole species of the
breed.

I still don't have
information on whether a soliton wave can propagate in a linear
medium, though I have references that say it is a non-linear
phenomenon that occurs in non-linear media.

Of course it can propagate in a linear medium. Solitons were first
reported in linear media - water - something like one hundred seventy
years ago. Solitons can induce non-linearity in otherwise linear
media. Solitons also interact in collision with a phase shift
afterwards. Solitons have been applied to data transmission in fiber
optics for a dozen years or more.

Your references are pretty sparse.

If you can convince me
that a wavefront coming to a Magic T doesn't see it as an impedance
discontinuity, we could perhaps post more about that--or not.

Consult Terman. He is quite compelling when it comes to describing
microwave plumbing. This hardly constitutes more than 4 pages total
reading, if you choose to move on beyond the first page of discussion.

But so far, your responses make me think you don't disagree with my
implicit suggestions:

True enough to a point.

that it's impossible to distinguish between the
condition of two cancelled waves that somehow still exist (huh?)

The elliptical huh? seems to be a curious toe in the water for many
here. Strange how a concept draws borders around energy it to make it
"disappear" simply because both contributions cancel. This is like
saying gravity disappears on a 1 square inch patch of earth when the
falling apple has come to rest on the ground. This is also akin to
the misnomer of zero-gravity environment of the astronauts in the
space shuttle.

For example (drawing away from G and towards V), if I were to place
two batteries in series opposition
- + + -
and connect a load to the two free terminals; sure, no current would
flow because there is no potential difference, but that numerical
combination doesn't make the batteries disappear. Yes, the condition
is indistinguishable from a load floating in null space, but we have a
priori knowledge of existing energy that informs us otherwise. If we
choose to be ignorant of the knowledge in that specific locality, the
map of all phase combinations around it will certainly bring it to our
attention again.

Beyond that, you're of course welcome to go off on whatever tangents
you wish. Basenote drift is the expected norm here; I engage in it
all the time myself.

The point of my going into a basenote drift is to present examples
that demonstrate what is necessary to answer your objections (like
providing two sources at one point that cancel on one side, but exist
independently on the other side of an interface). If those who
present their "theories" cannot meet these demonstrated
characteristics, then it is reasonable to reject their claims barring
their offering treatments that are equally compelling.

73's
Richard Clark, KB7QHC

On Apr 17, 12:33 am, Richard Clark wrote:
On 16 Apr 2007 17:50:10 -0700, "K7ITM" wrote:
....
I still
don't have a reference that a fiber optic cable is a TEM transmission
line, though I have others that say that it's not.

That example of the non-TEM fiber optic would be rare species indeed.
I've seen them, but that hardly constitutes the sole species of the
breed.

So give me a reference already. I find lots of references, including
ones that explain the propagation, that talk about TM, TE, hybrid, and
even quasi-TEM mode propagation in a fiber. What boundary conditions
are there in an optical fiber that give TEM mode?


I still don't have
information on whether a soliton wave can propagate in a linear
medium, though I have references that say it is a non-linear
phenomenon that occurs in non-linear media.

Of course it can propagate in a linear medium. Solitons were first
reported in linear media - water - something like one hundred seventy
years ago.

Solitons can induce non-linearity in otherwise linear
media. Solitons also interact in collision with a phase shift
afterwards. Solitons have been applied to data transmission in fiber
optics for a dozen years or more.

Your references are pretty sparse.

Yours seem non-existent. Mine at least did a good job explaining the
phenomena.

From Wikipedia, for example, about solitons:
"The stability of solitons stems from the delicate balance of
"nonlinearity" and "dispersion" in the model equations. Nonlinearity
drives a solitary wave to concentrate further; dispersion is the
effect to spread such a localized wave. If one of these two competing
effects is lost, solitons become unstable and, eventually, cease to
exist. In this respect, solitons are completely different from "linear
waves" like sinusoidal waves. In fact, sinusoidal waves are rather
unstable in some model equations of soliton phenomena. Computer
simulations show that they soon break into a train of solitons."

There is specific mention of the Kerr effect--a nonlinearity in
optical media that support soliton transmission. One of the
references I saw specifically said that solitons are solutions to non-
linear differential equations. Since the equations governing the
behaviour of waves derive from the properties of the propagation
medium, I expect that any medium that can propagate a soliton is
nonlinear. Another reference specifically addressed the nonlinearity
of water as a transmission medium, as a necessary part of its being
able to propagate solitons.



If you can convince me
that a wavefront coming to a Magic T doesn't see it as an impedance
discontinuity, we could perhaps post more about that--or not.

Consult Terman. He is quite compelling when it comes to describing
microwave plumbing. This hardly constitutes more than 4 pages total
reading, if you choose to move on beyond the first page of discussion.

I find nothing in the index of my "Radio Engineers' Handbook" by
Terman under either "Magic" or "Hybrid". Sorry. The three different
coaxial "Magic T" hybrid designs I DID find all do show an impedance
discontinuity: the junction of more than two lines of equal impedance
and/or impedance steps in through-lines. Sorry.

Time to move on.

Cheers,
Tom

On 17 Apr 2007 08:30:41 -0700, K7ITM wrote:

On Apr 17, 12:33 am, Richard Clark wrote:
On 16 Apr 2007 17:50:10 -0700, "K7ITM" wrote:
...
I still
don't have a reference that a fiber optic cable is a TEM transmission
line, though I have others that say that it's not.

That example of the non-TEM fiber optic would be rare species indeed.
I've seen them, but that hardly constitutes the sole species of the
breed.

So give me a reference already. I find lots of references, including
ones that explain the propagation, that talk about TM, TE, hybrid, and
even quasi-TEM mode propagation in a fiber. What boundary conditions
are there in an optical fiber that give TEM mode?

Hi Tom,

This is curious request indeed. Can you name any example of light
that is not TEM? Let's see, wikipedia's entry for TEM includes Fiber
Optics as example (along with the sources and illustrations for many
modes). TEM00 is the principle mode of the ubiquitous "single mode"
fiber optic that is laid in the millions of miles every year.

One vendor of Fiber modeling software
http://www.zemax.com
specifically at
http://www.zemax.com/kb/articles/154...MAX/Page1.html
offers:
"ZDC thanks Steve Dods of OptiWave Corporation for supplying the
SMF-28 fiber simulation data used in this article.

"In the article How to Model Coupling Between Single-Mode Fibers
SMF-28 single mode fiber is modeled using data from the
manufacturer's datasheet. The only data provided on the optical
radiation produced at 1.31 is the mode field diameter, which is
stated to be 9.2 ± 0.4 µm.

"As a result, the fiber mode of both launch and receiver fibers
was entered as a Gaussian (TEM0,0) mode of waist 4.6µ. The
resulting fiber coupling calculation agrees well with experimental
measurement."

Corning SMF-28 has been in production for nearly 20 years.

I still don't have
information on whether a soliton wave can propagate in a linear
medium, though I have references that say it is a non-linear
phenomenon that occurs in non-linear media.

Of course it can propagate in a linear medium. Solitons were first
reported in linear media - water - something like one hundred seventy
years ago.

Solitons can induce non-linearity in otherwise linear
media. Solitons also interact in collision with a phase shift
afterwards. Solitons have been applied to data transmission in fiber
optics for a dozen years or more.

Your references are pretty sparse.

Yours seem non-existent. Mine at least did a good job explaining the
phenomena.

To which there is scant difference as nearly every point you recite
has already been anticipated in my earlier post (shown above). Your
rebuttal that water is non-linear is already answered in this same
quote. If this is basenote drift, we are now into the treble clef.

If you can convince me
that a wavefront coming to a Magic T doesn't see it as an impedance
discontinuity, we could perhaps post more about that--or not.

Consult Terman. He is quite compelling when it comes to describing
microwave plumbing. This hardly constitutes more than 4 pages total
reading, if you choose to move on beyond the first page of discussion.

I find nothing in the index of my "Radio Engineers' Handbook" by
Terman under either "Magic" or "Hybrid". Sorry. The three different
coaxial "Magic T" hybrid designs I DID find all do show an impedance
discontinuity: the junction of more than two lines of equal impedance
and/or impedance steps in through-lines. Sorry.

Time to move on.

For others that are not moving on, but interested in the use and
issues of reflection to the source driving a Magic T, I quote work
from Q MEASUREMENTS FOR HIGH-Q CAVITIES
R. A. RAPUANO and J. HALPERN, MIT (1946):

"The heart of this equipment is the "magic T". This is an
eight-terminal network (Fig. 3) in waveguide or coax having
symmetry properties analogous to those of a "hybrid coil".
In the case of an ideal T, power entering the E aria is divided
equally between S1 and S2, both parts being out of phase; none
goes directly to H. Power entering the H arm is divided equally
between S1 and S2, with both parts now in phase; no power goes
directly to E. Power reflected from the loads on S1 and S2,
however, can be coupled from H to E, depending upon the magnitude
and phase of the terminal impedances on S1 and S In the case of
two short circuits the power going from H to E can be caused to
vary from zero to the full amount depending on their position
along the line. If a short circuit is placed on S1 and a resonant
cavity is placed on S2, then the power going from H to E is a
function of frequency. The power reflected back from H is the
difference between the input and the loss due to transmission
through E and absorption in the resonator."

Figure 3 (use fixed font):
S1
||
||
||
H ======== ======== E
||
||
||
S2

where the interior blank space represents the plumbing too difficult
to render here.

I would further offer that Walt is working on a fairly similar
treatment employing the "Rat Race" (alluded to as a Hybrid Coil in the
monograph extract above). The discussion above is germane in that
sense and would be beneficial to those who eventually see his
rebuttals to arguments pressed against him.

73's
Richard Clark, KB7QHC

On Apr 17, 2:57 pm, Richard Clark wrote:
....

Richard, it really doesn't much matter to me what modes fiber optic
cable supports. If there are types that support true TEM mode, I'd be
happy to hear about it. So far, though, I've followed links from over
a dozen searches and found NO reference that claims that true TEM mode
is supported by a fiber, be it single-mode or multi-mode. I've gone
to the Wikipedia pages you suggested and other pages there, and found
quite a bit of info about fiber optic cables and their modes. In all
that, I have found no claim that true TEM mode is supported. I
followed the link you provided to the simulation software provider,
and found only that they modeled a particular cable as having TEM 0,0
mode; nowhere could I see a claim that the cable modeled actually
propagates by true TEM mode. The way the article was worded sounded
to me like the TEM entry was an approximation. In my research, the
closest to a claim of true TEM mode I've found has been in one recent
article that says TEM would be the ideal, but the best anyone's been
able to do is quasi-TEM or TEM-like.

You're welcome to think it's true TEM if you wish, of course, but your
saying it, over and over if you wish, isn't going to be nearly as
convincing as if we can find one, even one, ligitimate reference that
claims true TEM.

Cheers,
Tom

K7ITM wrote:
No, it's about practicality. Convince me that calculations based
primarily on power (or energy) rather than on voltage and current
offer me something useful, with respect to TEM lines, and I might have
a closer look at them.

Assume you are dealing with light waves in free space
instead of RF waves in a transmission line. Would you
then find intensity (power density) calculations useful?
That's why optical physicists find them so useful.

Tom, are you familiar with an s-parameter analysis?

If so, it seems to me that b1 = s11(a1) + s12(a2) = 0
represent two wave components that immediately cancel
to zero when superposed at the impedance discontinuity.
Would you care to comment?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
K7ITM wrote:
No, it's about practicality. Convince me that calculations based
primarily on power (or energy) rather than on voltage and current
offer me something useful, with respect to TEM lines, and I might have
a closer look at them.

Assume you are dealing with light waves in free space
instead of RF waves in a transmission line. Would you
then find intensity (power density) calculations useful?
That's why optical physicists find them so useful.

Tom, are you familiar with an s-parameter analysis?

If so, it seems to me that b1 = s11(a1) + s12(a2) = 0
represent two wave components that immediately cancel
to zero when superposed at the impedance discontinuity.
Would you care to comment?

Cecil,

Most serious calculations by optical physicists are done through
Maxwell's Equations solvers. Intensity calculations are utterly
inadequate for exploring the details of high resolution imaging, for
example.

73,
Gene
W4SZ