Analyzing Stub Matching with Reflection Coefficients
 

Jim Kelley wrote:
It certainly is an interesting way of looking at things, Cecil. It's
certainly true that equal and opposite fields cancel. When that's the
case though it becomes problematic arguing that there are waves there.

The waves are certainly there and are measured in
the process of determining the values of the
s-parameters. That's enough proof of their
existence for me. If you deny their existence,
you are denying that the s-parameter measurement
procedure is valid.

Jim, what happens to the ExB power density in the
equal and opposite fields that cancel?
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

On Apr 18, 9:19 pm, Cecil Moore wrote:
Dr. Honeydew wrote:
Cecil Moore wrote:
A Bird wattmeter reads 100 watts forward and 100w reflected. The
current in the source is zero. The source is not only not sourcing any
forward power, it is also not sinking any reflected power.

What complete and utter Texas-size bullsh*t. It's obvious that the
source is sourcing the forward voltage wave, and it's sucking up
entire reverse voltage wave from the line.

And doing it while magically expending zero energy.
Perpetual motion is possible, after all.

If zero power is being dissipated in the source, it cannot
be sourcing the forward voltage wave and it cannot be
sucking up the reverse voltage wave.
--
73, Cecil http://www.w5dxp.com


Ah, I can see you didn't take me seriously. But I was dead serious.
It is absolutely not necessary for the source to be dissipating the
reverse wave it sucks up as heat.

A challenge: given a linear system consisting of a source of
impedance Z1, connected to a line (any length you want; any loss you
want) of impedance Z2, and the far end of the line connected to a load
of impedance Z3, or even to a different source of impedance Z3
(possibly different frequency, phase, and/or amplitude from the first
source). Give us one example, even one, that's not accurately
described by source Z1 launching waves into impedance Z2 in the
"forward" direction, plus whatever "reverse" wave is on the line doing
exactly the expected things at the Z2:Z1 boundary. In other words,
viewed from both sides, show us even one instance where the system is
not correctly analyzed with your S11--S12 equations for the Z1--Z2
interface. Show us even one instance where those equations will not
tell you exactly what happens to waves coming into that interface from
either direction, and in fact from both directions at once.

What the source does with the incoming wave is another matter,
independent of the Z1--Z2 interface. Whether it causes increased or
decreased dissipation of heat in the source depends on how the source
is made, and the characteristics (phase, amplitude, frequency, ...) of
the incoming wave.

From the labs,

Bunsen

Analyzing Stub Matching with Reflection Coefficients
 

Cecil Moore wrote:

Gene Fuller wrote:

Do you see the common factor in your response about "wave
interaction"? In all of your examples there is an interface or some
sort of discontinuity. Nobody argues that waves are forever
unchanging. However, those changes take place only through interaction
with interfaces or other discontinuities.


I don't disagree and I have gone on record as saying that
reflections only occur at physical impedance discontinuities.

You have also gone on record as saying is this:

4/19/07 6:12 AM
"The only thing s11(a1) and s12(a2) encounter are each other and that
interaction completely changes those two waves. The two waves cancel
and their energy components are re-distributed in the opposite
direction. s11(a1) and s12(a2) never encounter an impedance
discontinuity."

73, ac6xg

Analyzing Stub Matching with Reflection Coefficients
 

Cecil Moore wrote:

Jim, what happens to the ExB power density in the
equal and opposite fields that cancel?

Let's see E=0, and B=0; what power density, Cecil?

73, Jim AC6XG

Analyzing Stub Matching with Reflection Coefficients
 

Cecil Moore wrote:

That is the nature of EM waves, Gene. EM waves flowing
in opposite directions do NOT interact. However, their
reflected and transmitted components traveling in the
same direction can and do interact at an impedance
discontinuity.

Actually it's even more straightforward than that. They do interact
with a physical impedance discontinuity, and don't interact with each
other no matter which way they are traveling.

73, Jim AC6XG

Analyzing Stub Matching with Reflection Coefficients
 

Richard Clark wrote:
On Thu, 19 Apr 2007 14:56:33 GMT, Gene Fuller
wrote:

Do you have any connection with "optical physicists" beyond your reading
of Hecht and the Melles Griot website?

Hi Gene,

Aside from the number of us that have experience in the practice?

73's
Richard Clark, KB7QHC

Hi Richard,

I have not seen an optical physicist since I looked in the mirror this
morning.

8-)

73,
Gene
W4SZ

Analyzing Stub Matching with Reflection Coefficients
 

Cecil Moore wrote:
Gene Fuller wrote:
Help me out. How can we have scalars flowing in opposite directions?
If the waves can interact, as you claim, why does the associated
energy fail to interact and merely pass like ships in the night?

That is the nature of EM waves, Gene. EM waves flowing
in opposite directions do NOT interact. However, their
reflected and transmitted components traveling in the
same direction can and do interact at an impedance
discontinuity.



Cecil,

Progress!

All we need now is that you also understand that waves flowing in the
SAME direction do NOT interact unless there is an interface or other
discontinuity.

All sorts of things can happen at discontinuities. The detailed physical
mechanisms and the models are well understood.

73,
Gene
W4SZ

Analyzing Stub Matching with Reflection Coefficients
 

On Apr 19, 12:27 pm, Cecil Moore wrote:
Richard Harrison wrote:
How much energy will continue to enter the stub? Practically none
because there is no difference of potential between the source and the
reflection.

In a lossless stub, zero energy will continue to enter the stub.
In fact, in a lossless stub, the source can theoretically be
completely disconnected and everything remains the same
including 100% re-reflection of reflected waves by the new
open circuit.

I've always liked this example. By extension, on a line multiple
quarter wavelengths long, you can disconnect the line at ANY
of the voltage maxima and see exactly the same result as you
describe above. Are those travelling waves really crossing the
voltage maxima? Or are they being reflected? Or are they just
reflected at the maxima that actually occur at a discontinuity?
But there is no discontinuity at the source, so why would they
be reflected there? But if they are reflected at the
non-discontinuity at the source, then they should be reflected
at the non-discontinuities in the line as well. But wait, those
non-discontinuities are virtual opens and shorts, so maybe
they reflect at virtual ones as well. But no, it has been agreed
that reflections only happen at physical discontinuities.

And what if the stub is not a quarter (or multiple) wavelength
long? Then where does the reflection at the source occur?
At the last maximum or minimum along the line? Inside the
generator? It works for any length of line. Somehow the
generator knows exactly what reactance to supply?

It is definitely best to recognize that when the source impedance
is equal to the line impedance, there is no reflection at the
source. And it does not matter if the source impedance is
achieved with a circulator, a resistor, a multiplicity of resistors,
feedback, or what have you; there is no reflection if the
impedance is the same as the line. No discontinuity, no
reflection. A simple rule. Works at a load. Works at a
generator. Works along the line. Always works.

....Keith

Analyzing Stub Matching with Reflection Coefficients
 

Dr. Honeydew wrote:
Ah, I can see you didn't take me seriously. But I was dead serious.
It is absolutely not necessary for the source to be dissipating the
reverse wave it sucks up as heat.

Can a wave exist without energy? Where does the energy in the
sucked up wave go since it doesn't go into the source.

In other words,
viewed from both sides, show us even one instance where the system is
not correctly analyzed with your S11--S12 equations for the Z1--Z2
interface. Show us even one instance where those equations will not
tell you exactly what happens to waves coming into that interface from
either direction, and in fact from both directions at once.

You must have me confused with someone else. I'm a supporter
of the s-parameter analysis. It's others who have called
it "Gobbledegook" (sic).
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

Jim Kelley wrote:


Cecil Moore wrote:
... I have gone on record as saying that
reflections only occur at physical impedance discontinuities.

You have also gone on record as saying is this:

4/19/07 6:12 AM
"The only thing s11(a1) and s12(a2) encounter are each other and that
interaction completely changes those two waves. The two waves cancel
and their energy components are re-distributed in the opposite
direction. s11(a1) and s12(a2) never encounter an impedance
discontinuity."

There's no conflict between those two statements. s11(a1) and
s12(a2) indeed *NEVER* encounter an impedance discontinuity
since they originate already flowing *away from* the impedance
discontinuity. Any interference between two coherent collinear
EM waves traveling in the same path is a permanent interaction.
--
73, Cecil, w5dxp.com