Analyzing Stub Matching with Reflection Coefficients
 

Jim Kelley wrote:

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?

Play your silly word games if you will. Fields cannot
cancel unless those fields first exist. Assume E1xB1
joules/sec associated with the first field and E2xB2
joules/sec associated with the second field. The fields
cancel. What happens to the E1xB1 joules/sec and the
E2xB2 joules/sec? Hint: Their energy components are
redistributed in a direction that allows constructive
interference. In a transmission line, there is only
one other direction available.
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

Jim Kelley wrote:
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.

Sorry Jim, the s11(a1) wave and s12(a2) wave are *NEVER*
incident upon an impedance discontinuity yet they cancel.
How do two waves cancel without interacting?
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

On Apr 19, 3:44 pm, Cecil Moore wrote:
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.

You are getting close to the truth. Yes, the forward and reverse
travelling waves are not necessarily moving energy. The Bird
wattmeter, despite its name, is computing a number with the
dimension of watts, but which does not necessarily represent
energy flowing (it represents flowing energy when the indicated
value is 0 in one direction or the other).

This will probably (I understate) be hard to accept but is the
only reasonable conclusion after examining a large number
of experiments and trying to rationalize the answer
to "Where does the energy in the reflected wave go?" Once
it becomes clear that there is no good answer to that
question, the only possible conclusion is that the question
is invalid and the roots of its invalidity lie in the assumption
of energy in the reflected wave.

....Keith

Analyzing Stub Matching with Reflection Coefficients
 

Gene Fuller wrote:
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.

Please stop implying things that I have never said. When I
asserted that reflections only happen at a physical impedance
discontinuity, that implies that interaction can only happen
at a physical impedance discontinuity. It is impossible to
get two coherent waves flowing in the same direction except
at a physical impedance discontinuity.

Assume b1 = s11(a1) + a12(s2) = 0

What I have said is that s11(a1) and s12(a2) are wave components
that cancel without ever being incident upon an impedance discontinuity.
Those two wave components originate at the impedance discontinuity
flowing *AWAY FROM* the impedance discontinuity. They are canceled
in a delta-t, i.e. a very short time. Those two waves are the result
of interaction at the impedance discontinuity but neither of them
ever interacted with the impedance discontinuity because they
originated at the impedance discontinuity.
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

Keith Dysart wrote:
Are those travelling waves really crossing the
voltage maxima? Or are they being reflected?

There is no impedance discontinuity - therefore no
reflections.

But there is no discontinuity at the source, ...

You are still making the same mistake as you have from
the beginning. There is a discontinuity at the source.
In your example, it is called the load-line. The load-
line in the previous example is source voltage divided
by zero, i.e. infinity. That's what the reflected wave
sees.

It is definitely best to recognize that when the source impedance
is equal to the line impedance, there is no reflection at the
source.

You have been asserting that since your first posting and it
is a *FALSE STATEMENT* as proved by the latest example.
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

Cecil Moore wrote:

Fields cannot
cancel unless those fields first exist.

Please clarify for us the distinction between canceled fields, and
fields which don't exist.

There is no energy traveling in the direction of fields that cancel;
E1xB1 and E2xB2 in this example.

Assume E1xB1
joules/sec associated with the first field and E2xB2
joules/sec associated with the second field. The fields
cancel. What happens to the E1xB1 joules/sec and the
E2xB2 joules/sec?

Since the fields cancel, and energy does not travel in the company of
nonexistent fields, there is no energy here with which to concern
ourselves.

Hint: Their energy components are
redistributed in a direction that allows constructive
interference. In a transmission line, there is only
one other direction available.

Producing a result which can only occur when there is no energy
traveling in the direction of E1xB1 and E2xB2.

73, Jim AC6XG

Analyzing Stub Matching with Reflection Coefficients
 

Keith Dysart wrote:
You are getting close to the truth. Yes, the forward and reverse
travelling waves are not necessarily moving energy.


How in the world is EM traveling waves existing without
energy getting close to the truth? Seems it is getting
closer to fantasy than anything else.

The Bird
wattmeter, despite its name, is computing a number with the
dimension of watts, but which does not necessarily represent
energy flowing (it represents flowing energy when the indicated
value is 0 in one direction or the other).

If the Bird is properly used, it indicates joules flowing
past a point in one second in the environment for which it
is calibrated. If EM energy waves ever stop flowing, they
cease to be EM waves. The boundary conditions for EM waves
will not permit them to travel at any other speed than
d(VF) nor exist devoid of energy.

This will probably (I understate) be hard to accept but is the
only reasonable conclusion after examining a large number
of experiments and trying to rationalize the answer
to "Where does the energy in the reflected wave go?" Once
it becomes clear that there is no good answer to that
question, the only possible conclusion is that the question
is invalid and the roots of its invalidity lie in the assumption
of energy in the reflected wave.

False, false, and false. *Every* EM wave is associated with ExB
joules/sec. The energy supporting a reflected EM wave is either
reflected or transmitted or dissipated. Those EM waves do not
care a whit if you never figure them out.
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

Cecil Moore wrote:

How do two waves cancel without interacting?

No interaction is required in order for fields to cancel. Only that
they occupy the same space at the same time and be of the correct
amplitude and phase.

73, Jim AC6XG

Analyzing Stub Matching with Reflection Coefficients
 

On Apr 19, 12:44 pm, Cecil Moore wrote:
Dr. Honeydew wrote:

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

Ah, thank you. Then it follows directly from that, that when you
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.
you were not disallowing the fact that the source, which is matched to
the line, sucks up the entire reverse wave from the line. I'm happy
to see we agree on that little point after all.

Fallacies of the, "if the source absorbs the reverse wave, it must be
dissipated as heat," school: Start with a source which is a voltage
generator, 141.4Vrms sinewave, in series with a 50 ohm resistor.
Connect it to a 50 ohm load, and you have 100 watts dissipated inside
the source and 100 watts dissipated in the load. Put a 50 ohm
lossless line between the source and the load. We now have a
70.71Vrms wave from the source to the load, and no reflected. Assume
the line is 1/4 wave long; replace the load with a short. A moment
later, steady state is reached and the dissipation in the source's 50
ohm resistor dropped from 100W to 0W. We may be tempted to say that
source did not absorb the return wave and is no longer supplying the
forward wave. But that requires complete reflection of the return
wave at the interface between the source and the line. Ah, but there
is an infinite set of conditions under which the same should be
true. What if we make the line 1/2 wave long, still shorted at the
far end? In steady state, the source is still apparently delivering
no power to the line, but now, instead of it dissipating NO power,
it's suddenly dissipating 400 watts! In the line, though, we still
see 100 watts of forward power, and 100 watts of reverse power.

Ooops. The "if the source absorbs the reverse wave, it must be
dissipated as heat" school ... better go back to school. Or to the
lab. Or SOMEwhere else, till they get it figured out. It didn't hold
water when Dr. Slick (remember him?) tried to push it on us, and it
doesn't hold water now.

More fun: the guts of my source are now a 282.8V source and the 50
ohm resistor, feeding a fairly long piece of 50 ohm transmission line
to the front panel connector. The line has 6.02dB loss. Now back to
the original situation with 1/4 wave of 50 ohm line, shorted at the
far end, connected to the generator's output connector. NOW are you
going to say that the reverse wave on the 1/4 wave line stops when it
gets back to the generator? What if I put even a couple inches of
line between the guts of the source and the front panel connector,
does the reverse wave on the external line stop when it gets to the
front panel connector?

I repeat: [In the case of a line connected to a source, with the
impedance of the two matched--not conjugate] It's obvious that the
source is sourcing the forward voltage wave, and it's sucking up the
entire reverse voltage wave from the line.

What happens to that reverse voltage wave inside the source depends on
what's in the guts of the source.

From the lab,

Bunsen

Analyzing Stub Matching with Reflection Coefficients
 

On Thu, 19 Apr 2007 14:11:21 -0700, Jim Kelley
wrote:

Cecil Moore wrote:

How do two waves cancel without interacting?

No interaction is required in order for fields to cancel. Only that
they occupy the same space at the same time and be of the correct
amplitude and phase.

And are put into a load.

As waves are completely independant, then they never interact. A load
is required to reveal the cancellation. No load, and any issue of
cancelling fields is strictly limited to what goes on between the
ears.

73's
Richard Clark, KB7QHC