Constructive interference in radiowave propagation
 

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....

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....

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....

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.]

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.

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

Constructive interference in radiowave propagation
 

Cecil Moore wrote:


Partially reflective surfaces cannot, by themselves,
reflect 100% of the incident energy.

They can and certainly do when no energy is passing through the
reflecting surface. In such a case the only energy conveyed by the
wave is that which is reflected. The 100% number comes not in a
single bounce, or from a single wavefront. But I don't expect you to
understand this.

The waves existed along with their energy components before
they were canceled.

I believe your misunderstanding probably lies somewhere within that
statement. It does not convey concise meaning.

What happens to those energy components
after the waves are canceled.

Where there are waves, there is energy. Where there are no waves,
there is no energy. Show me the canceled waves.

73, Jim AC6XG

Constructive interference in radiowave propagation
 

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

Constructive interference in radiowave propagation
 

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

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
I really do appreciate your courteous and patient offer. But in fact,
you have already waded us through that so many times it's kinda funny
that you hope it will somehow turn out differently this time.

We have never discussed the point in the analysis that
I would like to discuss next. It will be brand new
territory. What have you got to lose?
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

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

Constructive interference in radiowave propagation
 

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.

Please stop the unfair innuendo. You have yet to see me say that
waves can become perfectly collinear, except at an impedance
discontinuity. I have gone out of my way to say reflections
happen only at a physical impedance discontinuity. Waves become
perfectly collinear because of reflections at a physical
impedance discontinuity. I don't know how you can possibly
be confused regarding what I said.

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.

Please stop the unfair innuendo. You have yet to see me say that
waves do not cancel immediately at the point of reflection. That's
because they are canceled immediately, like delta-t, after the
reflection. They exist for such a short time that they cannot even
be seen on an o'scope. There existence can only be deduced because
if they didn't exist, nothing would happen at a physical impedance
discontinuity.

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.

Not sure what you are getting at. All those waves are associated
with joules/second. I am not trying to replace anything. I am
merely adding an energy analysis to the voltage analysis. The
voltage analysis remains exactly the same as it has always been.

In an S-parameter analysis, if you square any of the normalized
voltage terms, you get joules/sec (power). If you square any
of the voltage reflection or transmission coefficients, you
get the power reflection coefficient. The S-Parameter analysis
seems to have been designed with power in mind. The HP Ap Note
says, "The previous four equations show that s-parameters are
simply related to power gain and mismatch loss, quantities
which ARE OFTEN OF MORE INTEREST than the corresponding
voltage functions." What do you suppose HP meant by, "ARE
OFTEN OF MORE INTEREST" regarding the power components?
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Jim Kelley wrote:
They can and certainly do when no energy is passing through the
reflecting surface. In such a case the only energy conveyed by the wave
is that which is reflected. The 100% number comes not in a single
bounce, or from a single wavefront. But I don't expect you to
understand this.

I fully understand it Jim. I'm willing to take the time
to explain it to you with s-parameter examples, but you
have refused to listen. One wonders what you are afraid
of and what you have to lose except face.

Where there are waves, there is energy. Where there are no waves, there
is no energy. Show me the canceled waves.

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

s11(a1) and s12(a2) are the two waves that are being
canceled. They exist sum to zero. Have you ever done
any phasor or vector addition?
--
73, Cecil http://www.w5dxp.com

Constructive interference in radiowave propagation
 

Cecil Moore wrote:


We have never discussed the point in the analysis that
I would like to discuss next. It will be brand new
territory. What have you got to lose?

Time, patience, energy......

As Jack Nicholson once said, "I'd rather stick needles in my eyes".

ac6xg

Constructive interference in radiowave propagation
 

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