Analyzing Stub Matching with Reflection Coefficients
 

On Apr 26, 1:24 am, Cecil Moore wrote:
Can we at least agree that a class-C amplifier is not linear?

By this, do you mean that the input to output transfer function
of a class-C amplifier is not linear?

Or do you mean that the output aspects of a class-C amplifier
can not be modelled as a linear circuit?

The former is certainly true, but for the latter, it seems to me
a first order model of the output circuit would be a voltage
controlled current sink (the tube), a constant voltage source
(the power supply), an RFC, a coupling capacitor and an
output filter constructed of inductors and capacitors; all of
which are linear components.

....Keith

Analyzing Stub Matching with Reflection Coefficients
 

Keith Dysart wrote:
On Apr 26, 1:24 am, Cecil Moore wrote:
Can we at least agree that a class-C amplifier is not linear?

By this, do you mean that the input to output transfer function
of a class-C amplifier is not linear?

It's a little more subtle than that. I mean that the
output of an active dynamic class-C amplifier does not
lend itself to passive superposition. The component of
the sums is not the sum of the components.

Or do you mean that the output aspects of a class-C amplifier
can not be modelled as a linear circuit?

If a class-C amplifier is modeled as a linear circuit,
the model is wrong.

The former is certainly true, but for the latter, it seems to me
a first order model of the output circuit would be a voltage
controlled current sink (the tube), a constant voltage source
(the power supply), an RFC, a coupling capacitor and an
output filter constructed of inductors and capacitors; all of
which are linear components.

But the model bears little resemblance to the actual
active dynamic source which has been my objection all
along. When the tube is off, the source impedance is
essentially infinite. It is like the energy tick provided
by the weights in a pendulum clock. One can assume that
the linear pendulum is the energy source but the weights
are actually the energy source and that energy is
delivered as a step function pulse.
--
73, Cecil http://www.w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

Dave wrote:


no, i heartily DO believe in superposition. what i hate the misnomer
'standing waves' that has misled many non technical people to an incorrect
view of how waves work.



Dave,

You say the words, but you gotta walk the talk.

When superposition applies, the superposed function is completely
equivalent to the sum of the components. There are no remaining hidden
variables still lurking in the original components, invisible to the
standing wave.

When two traveling waves combine to form a standing wave, the standing
wave result contains *all* the information and properties there are to
be had. The standing wave is just as valid as the two component waves
taken together.

Now Cecil (and others) may immediately come along and assert that we can
take one traveling wave at a time and yadda, yadda, yadda. Sure we can,
but it is now a different setup. He may also yammer on about all sorts
of special cases, with transients, circulators, non-linear setups, and
so on. Superposition does not always apply, but when it does, it works.

I have said many times that all of this is strictly a matter of
mathematical convenience. In that regard there is some agreement with
your assertion that standing waves were first recognized as a matter of
expediency. However, standing waves are *not* an approximation. A
correct standing wave function works just fine as a solution to the
standard wave equation. No traveling waves are needed at all, but you
can use the completely equivalent set of traveling waves if you prefer.

73,
Gene
W4SZ

Analyzing Stub Matching with Reflection Coefficients
 

Gene Fuller wrote:
When superposition applies, the superposed function is completely
equivalent to the sum of the components. There are no remaining hidden
variables still lurking in the original components, invisible to the
standing wave.

When two traveling waves combine to form a standing wave, the standing
wave result contains *all* the information and properties there are to
be had. The standing wave is just as valid as the two component waves
taken together.

Let me remind you of what you said earlier - that all phase
information disappears from the phase of the standing wave
and that the phase information from the component waves is
contained in the amplitude of the standing wave. Conversely,
the amplitude information from the component waves is contained
in the phase of the standing wave. This is why standing wave
current cannot be used to measure phase shift and why standing
wave amplitude cannot be used to measure the "current drop"
through a loading coil.

Roy's and Tom's measured "current drop" is actually phase
delay information. Their phase measurement is actually
information about the amplitudes of the forward and
reflected waves. They apparently didn't (and still don't)
understand that fact.

Now Cecil (and others) may immediately come along and assert that we can
take one traveling wave at a time and yadda, yadda, yadda. Sure we can,
but it is now a different setup.

This seems to contradict what you said in the paragraph just above.
Taking the component waves together is either valid or it is not,
no if's and's, or but's.

I have said many times that all of this is strictly a matter of
mathematical convenience. In that regard there is some agreement with
your assertion that standing waves were first recognized as a matter of
expediency. However, standing waves are *not* an approximation. A
correct standing wave function works just fine as a solution to the
standard wave equation.

The problem is that some people have been seduced by the standing
wave solution not realizing that the constant standing wave phase
cannot be used to measure phase shift. Roy's and Tom's measurements
of standing wave phase through a loading coil are meaningless yet,
to the best of my knowledge, you have not voiced an opinion about
those bogus measurements.

No traveling waves are needed at all, ...

The question is not whether, when properly implemented, a standing
wave analysis yields valid results. The questions a

1. Can the component forward and reverse traveling waves be used
to obtain a valid solution? If the answer is no, then the
superposition principle is invalid. If the answer is , yes,
then why do you object?

2. Have some people made errors in their analysis using standing
waves? The answer is obviously, yes, since standing wave phase
was used for loading coil phase delay invalid "measurements".
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

Roy Lewallen wrote:
Once again, I request that anyone who is interested in seeing what I
wrote please look it up at groups.google.com, and not rely on Cecil's
recollection and creative interpretation of what I wrote.

Incidentally, everyone (including me) was wrong in the
discussions back in 2003. There were two sides to the
argument and both sides were partially right and partially
wrong. The correct answer lies somewhere in between the
two positions.

The key to understanding the phase shift through a
loading coil is in first understanding how a stub
that is physically 41 degrees long can cause 90
degrees of phase shift. Here's an example:

---30 deg 450 ohm line---+---11 deg 50 ohm line---open

The above stub is physically 41 degrees long and
electrically 90 degrees long. Understanding how that
is possible is the key to understanding how 30 degrees
of coil and 11 degrees of stinger can resonate as if
it were 90 degrees long.

There is NOT (90 - 11 = 79) degrees of phase shift through
the coil.

There is NOT zero degrees of phase shift through the coil.

There *IS* 30 degrees of phase shift through the coil.
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

Cecil Moore wrote:


Let me remind you of what you said earlier -


Cecil,

Thanks, but no thanks. I know exactly what I said, and have consistently
said the same thing.

(Life is easier when one does not need to keep inventing new tall tales
to cover up the previous tall tales.)

8-)

73,
Gene
W4SZ

Analyzing Stub Matching with Reflection Coefficients
 

Gene Fuller wrote:
Cecil Moore wrote:
Let me remind you of what you said earlier -

Thanks, but no thanks. I know exactly what I said, and have consistently
said the same thing.

Unfortunately, some of your guru friends say just the
opposite.
--
73, Cecil, w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

"Cecil Moore" wrote in message
...
Tom Donaly wrote:
Yep, Darwin was a tool of the Devil, the Earth is flat, faith can heal
all disease, and the Earth is 6000 years old.

You forgot: Forward waves and reverse waves interact to form
standing waves which is what would have to happen to satisfy
some of the assertions made in this thread.
--
73, Cecil http://www.w5dxp.com

NO THEY DON'T! the traveling waves do not interact! Your measurement of
the superimposed voltages or currents makes you THINK they interact, but you
are just fooling yourself.

note, the superposition theorem says basically that the response of a linear
network to several input signals can be represented as the sum of the
responses of the individual signals. it says nothing about being able to
take apart a signal to regain the separate inputs once you have added them
together.

i.e. suppose you have a linear system f() and feed it with signals x(t) and
y(t). the superposition theorem says:
f(x(t)+y(t))=f(x(t))+f(y(t))

so lets say the function 'f' just doubles the input voltage. and to make it
really simple assume x(t) and y(t) are just constant values x and y. now
answer the following question using superposition:

Given f(x+y)=4
And f(x)+f(y)=4
Find x and y (show your work)

Give up? Good for you! now you understand that knowing the sum does NOT
tell you the components, even in a very simple linear system.

Analyzing Stub Matching with Reflection Coefficients
 

Dave wrote:
"Cecil Moore" wrote:

Tom Donaly wrote:
Yep, Darwin was a tool of the Devil, the Earth is flat, faith can heal
all disease, and the Earth is 6000 years old.

You forgot: Forward waves and reverse waves interact to form
standing waves which is what would have to happen to satisfy
some of the assertions made in this thread.

NO THEY DON'T! the traveling waves do not interact! Your measurement of
the superimposed voltages or currents makes you THINK they interact, but you
are just fooling yourself.

Dave, just to be clear, here's the list I added to.

1. Darwin was a tool of the Devil.
2. The Earth is flat.
3. Faith can heal all disease.
4. The Earth is 6000 years old.
5. Forward waves and reverse waves interact to form standing waves.

It is a list of foolish absurd notions - so I agree with you.
--
73, Cecil http://www.w5dxp.com

Analyzing Stub Matching with Reflection Coefficients
 

On Apr 26, 9:14 am, Cecil Moore wrote:
Keith Dysart wrote:
Or do you mean that the output aspects of a class-C amplifier
can not be modelled as a linear circuit?

If a class-C amplifier is modeled as a linear circuit,
the model is wrong.

Well, all models are wrong. The question is, "Are they good
enough?"

It seems to me
a first order model of the output circuit would be a voltage
controlled current sink (the tube), a constant voltage source
(the power supply), an RFC, a coupling capacitor and an
output filter constructed of inductors and capacitors; all of
which are linear components.

But the model bears little resemblance to the actual
active dynamic source which has been my objection all
along. When the tube is off, the source impedance is
essentially infinite.

The impedance of an ideal current sink is always infinite,
whether it is conducting no current or any current. So the
first level model I proposed above aligns with your
statement.

Certainly the model I described is linear. Is there some
other fault in the model that makes it sufficiently incorrect
to be unusable?

....Keith