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