Jim Lux wrote in
:

Owen Duffy wrote:

....
Actually, in modern systems with very complex signals, there are more
meaningful tests like noise power ratio with a notch that look for
spectral regrowth. The two tone test has the advantage of being
moderately easy to perform for middling performance
amplifiers/devices.
But if you're looking for very high performance, such things as
generating the two tones without one generator interfering with the
other get to be challenging.

Noted.


I suspect that the issue of transfer linearity is a red herring to
your proposition about the Thevenin equivalent of an RF PA, but if
you do depend on arguing that the transfer characteristic of a Class
C RF PA is linear, I think you are on shaky ground.

I don't know that the concept of a Thevenin equivalent (a linear
circuit theory concept) really has applicability to "box level"
models, except over a very restricted range, where one can wave one's
hands and ignore the nonlinearities as irrelevant to the question at
issue. Sure, over a restricted dynamic range and bandwidth and
restricted class of input signals, a Class C (or class E or Class F or
E/F1, or a fancy EER system) can be adequately modeled as a linear
ideal amplifier.

I agree with you. I am not implying that you cannot design a PA with
controlled equivalent source impedance, but you don't do they way most
ham PAs are designed.

As I understand it, Walt's proposition is that the Thevinin equivalent
source impedance (at the device terminals) of the PA is equal to the
conjugate of Zl (at the device terminals) as a consequence of adjustment
of the PA for maximum power output, a twist on the Jacobi MPT theorem.
For that model to be generally useful in explaining behaviour of the PA
in the presense of 'reflections', it would need to be true for a wide
range of load impedances.



The real question is what is the value of that model. If the model
provides conceptual understanding of some underlying problem, great.
For instance, it might help with a link budget. If the model helps
design a better amplifier, great. The model might allow prediction of
behavior; so that you can, for instance, detect a fault by the
difference between model and actual observation, as Richard mentioned
with the harmonic energy detector.

I think it goes to whether Walt's proposition and observations apply in
general, and then a valid explanation for what happens.

Owen

Richard Harrison wrote:
Owen Duffy wrote:
"Richard, I accept that you are committed to your view. Let`s leave it
at that."

Owen is "throwing in the towel' but not admitting error.

I have no allegiance to a particular view. I am happy to view things
from another`s perspective. Owen mught do the same.

Owen Duffy also wrote:
"I understand your position to be that the behavior of a tank circuit is
independent of the transfer linearity of the active device...but
asserting that things are linear because there are no harmonics is wrong
and saying so is no support for your argument."

Owen has it wrong. The final amplifier is linear because its output is
an exact replica of its input except for amplitude, or close enough so.

When the waveshape of the output signal from an amplifier varies in any
respect other than amplitude from the waveshape of the signal feeding
the amplifier, the amplifier is distorting the signal.

Sinewave a-c is considered the perfect waveform. It consists of a single
frequency. Any other waveform consists of more than one frequency, So
the presence or absence of harmonics in addition to the fundamental is a
clear indication of distortion. Anyone can confirm waveform using an
oscilloscope.

Best regards, Richard Harrison, KB5WZI



From _Filtering in the Time and Frequency Domains_ by Herman J.
Blinchikov and Anatol I. Zverev: "A system is linear if the input
c1f1(t)+ c2f2(t) produces and output c1g1(t)+ c2g2(t) for all
f1(t) and f2(t), when it is known that an input f1(t) produces an
output g1(t) and an input f2(t) produces and output g2(t). The c1 and
c2 are arbitrary constants but may be complex numbers. This property of
superposition is characteristic of linear systems." You're ignoring the
addition part of the concept of linearity, Richard. Moreover, the
functions f1(t) and f2(t) don't have to be sine waves; the concept
is more general than that. Finally, read Richard Clark's post.
A sine wave out doesn't prove a sine wave in.
73,
Tom Donaly KA6RUH

Richard Clark wrote:
"The presumption (forced or otherwise) is that the output is sinusoidal.
In fact, the cathode current of the amplifier proves quite positively
that only a pulse in, 180 degrees of sinewave, or even less, is
sufficient to generate a remarkably clean sinewave at the final`s
output."

That is a remarkably clear statement of the behavior of a Class C
amplifier. The amplifier acts as a generator of a sinewave which is
synchronized by its input signal instead of being an accurate reproducer
of the waveform at its input.

The less than half wave of current flow of the Class C amplifier allows
an efficiency exceeding 50%. Walt Maxwell`s tests show that the Class C
amplifier sticks to the parameters of a Thevenin source.

The question of "what is the source impedance" presented to a load by
the amplifier? is answered, not by magic, but by the maximum power
transfer theorem. The amplifier must be adjusted to deliver all its
available power. Then, the output impedance of the amplifier is simply
the conjugate of the load impedance which is easily measured.

Best regards, Richard Harrison, KB5WZI

On Wed, 18 Jun 2008 03:39:54 -0500, (Richard
Harrison) wrote:

The question of "what is the source impedance" presented to a load by
the amplifier? is answered, not by magic, but by the maximum power
transfer theorem. The amplifier must be adjusted to deliver all its
available power. Then, the output impedance of the amplifier is simply
the conjugate of the load impedance which is easily measured.

Hi Richard,

MPT Conjugate Match Z Match

You can NOT achieve the COMBINATION of any two, much less all three
with a Class C amplifier. This is like checking all three possible
answers on a multiple choice exam. It follows that source impedance
has not been answered here as a qualifiable (which is certainly not
what I was looking for).

I will take it that you don't know what the source impedance is as a
quantifiable either. That is, unless you unwind all the confounding
statements and remove those in error. There cannot be three,
simultaneous quantifiables of differing values.

73's
Richard Clark, KB7QHC

"Owen Duffy" wrote in message
...
Jim Lux wrote in
:

Owen Duffy wrote:

...
Actually, in modern systems with very complex signals, there are more
meaningful tests like noise power ratio with a notch that look for
spectral regrowth. The two tone test has the advantage of being
moderately easy to perform for middling performance
amplifiers/devices.
But if you're looking for very high performance, such things as
generating the two tones without one generator interfering with the
other get to be challenging.

Noted.


I suspect that the issue of transfer linearity is a red herring to
your proposition about the Thevenin equivalent of an RF PA, but if
you do depend on arguing that the transfer characteristic of a Class
C RF PA is linear, I think you are on shaky ground.

I don't know that the concept of a Thevenin equivalent (a linear
circuit theory concept) really has applicability to "box level"
models, except over a very restricted range, where one can wave one's
hands and ignore the nonlinearities as irrelevant to the question at
issue. Sure, over a restricted dynamic range and bandwidth and
restricted class of input signals, a Class C (or class E or Class F or
E/F1, or a fancy EER system) can be adequately modeled as a linear
ideal amplifier.

I agree with you. I am not implying that you cannot design a PA with
controlled equivalent source impedance, but you don't do they way most
ham PAs are designed.

As I understand it, Walt's proposition is that the Thevinin equivalent
source impedance (at the device terminals) of the PA is equal to the
conjugate of Zl (at the device terminals) as a consequence of adjustment
of the PA for maximum power output, a twist on the Jacobi MPT theorem.
For that model to be generally useful in explaining behaviour of the PA
in the presense of 'reflections', it would need to be true for a wide
range of load impedances.



The real question is what is the value of that model. If the model
provides conceptual understanding of some underlying problem, great.
For instance, it might help with a link budget. If the model helps
design a better amplifier, great. The model might allow prediction of
behavior; so that you can, for instance, detect a fault by the
difference between model and actual observation, as Richard mentioned
with the harmonic energy detector.

I think it goes to whether Walt's proposition and observations apply in
general, and then a valid explanation for what happens.

Owen

Owen, on whether my observations apply in general, if you re-read the
summarizing paragraph on my Chapter 19A you'll see that I've made measurements
of the source impedance of two different xmtrs with several different complex
impedance loads. All measurements showed the source impedance equal to the load
impedance when all available power is delivered to the load.

As to the explanation, Richard H said it well. When all available power is
delivered, according to the maximum power transfer theorem the source impedance
equals the load impedance. My measurements have proved this to be true in
determining the source impedance of the xmtrs I measured.

Walt, W2DU

"Richard Clark" wrote in message
news
On Wed, 18 Jun 2008 03:39:54 -0500, (Richard
Harrison) wrote:

The question of "what is the source impedance" presented to a load by
the amplifier? is answered, not by magic, but by the maximum power
transfer theorem. The amplifier must be adjusted to deliver all its
available power. Then, the output impedance of the amplifier is simply
the conjugate of the load impedance which is easily measured.

Hi Richard,

MPT Conjugate Match Z Match

You can NOT achieve the COMBINATION of any two, much less all three
with a Class C amplifier. This is like checking all three possible
answers on a multiple choice exam. It follows that source impedance
has not been answered here as a qualifiable (which is certainly not
what I was looking for).

I will take it that you don't know what the source impedance is as a
quantifiable either. That is, unless you unwind all the confounding
statements and remove those in error. There cannot be three,
simultaneous quantifiables of differing values.

73's
Richard Clark, KB7QHC

Hi Richard C,

Am I hearing you correctly? Are you disagreeing with Richard H? Are you saying
that maximum power transfer, conjugate match at the output, and Z match cannot
occur simultaneously? Are you serious? As I understand Everitt's statement of
the maximum-power-transfer theorem, when the maximum available power is being
transferred to the load there is a conjugate match. Does this not also mean
there is a 'Z' match? Can't 'Z' be assumed to be the impedance of the source as
well as the load?

Walt, W2DU

Richard Clark wrote:
"I will take it that you don`t know what the source impedance is as a
quantifiable either."

Terman wrote on page 76 of his 1955 opus:
"Alternatively, a load impedance may be matched to a source of power in
such a way as to make the power delivered to the load a maximum. (The
power delivered under these conditions is termed the "available power"
of the power source.) This is accomplished by making the load impedance
the conjugate of the generator as defined by Thevenin`s theorem. That
is, the load impedance must have the same magnitude as the generator
impedance, but the phase angle of the load is the negative of the phase
angle of the generator impedance."

Best regards, Richard Harrison, KB5WZI

On Wed, 18 Jun 2008 11:59:40 -0400, "Walter Maxwell"
wrote:

Hi Richard C,

Am I hearing you correctly? Are you disagreeing with Richard H? Are you saying
that maximum power transfer, conjugate match at the output, and Z match cannot
occur simultaneously?

Hi Walt,

For a Class C tube amplifier.

All descriptions of tune-up for a Class C tube amplifier describe a
qualitative MPT as this classic method offers absolutely no
information about the quantitative degree of initial mismatch, nor
subsequent proximate match. In other words, there are no quantitative
values of load impedance revealed by this method. It may even be said
that the classic tune-up only describes "an attempt" at MPT; as it
may, in fact, not even achieve anything more than Mediocre Power
Transfer. After peaking the grid and dipping the plate, I have
observed many different peaks and dips for many various loads to know
that not all loads obtained all available power.

The classic description of a tune-up is based on qualitative
assumptions and the amplifier is brought into its best attempt, which
is not demonstrably efficient, nor even proven to be "matched"
conjugately or by impedance. This takes more information (so far
unrevealed) obtained by current into the known load (unrevealed), and
power into the source (unrevealed). No one other than myself has
expressed the loss of the source because no one else has ever
enumerated its resistance (a topic commonly hedged and avoided) Hence
discussion of efficiency is lost in the woods and correlation to
MPT/Z/Conjugation is equally doomed to ambiguity.

Are you serious? As I understand Everitt's statement of

Everitt notwithstanding, Lord Kelvin trumps him with
"when you cannot express it in numbers, your knowledge is of a
meagre and unsatisfactory kind"
This thread has suffered from a lack of measurables that are not that
difficult to obtain.

So, to return to my very specific question:
What is the source resistance of any power amplifier?
I will further loosen constraints (if that isn't loose enough)
For any match?

One complex number is sufficient, and certainly that value will
resolve all imponderabilities is what I am asking for.

73's
Richard Clark, KB7QHC

"Richard Harrison" wrote in message
...
Richard Clark wrote:
"I will take it that you don`t know what the source impedance is as a
quantifiable either."

Terman wrote on page 76 of his 1955 opus:
"Alternatively, a load impedance may be matched to a source of power in
such a way as to make the power delivered to the load a maximum. (The
power delivered under these conditions is termed the "available power"
of the power source.) This is accomplished by making the load impedance
the conjugate of the generator as defined by Thevenin`s theorem. That
is, the load impedance must have the same magnitude as the generator
impedance, but the phase angle of the load is the negative of the phase
angle of the generator impedance."

Best regards, Richard Harrison, KB5WZI

That's the way I understand it too, Richard. But also works in the opposite
direction too, by adjusting the source impedance to have the same magnitude and
opposite phase of the load impedance. This is the procedure I used to prove the
value of the source impedance.

Walt, W2DU

"Richard Clark" wrote in message
...
On Wed, 18 Jun 2008 11:59:40 -0400, "Walter Maxwell"
wrote:

Hi Richard C,

Am I hearing you correctly? Are you disagreeing with Richard H? Are you
saying
that maximum power transfer, conjugate match at the output, and Z match
cannot
occur simultaneously?

Hi Walt,

For a Class C tube amplifier.

All descriptions of tune-up for a Class C tube amplifier describe a
qualitative MPT as this classic method offers absolutely no
information about the quantitative degree of initial mismatch, nor
subsequent proximate match. In other words, there are no quantitative
values of load impedance revealed by this method. It may even be said
that the classic tune-up only describes "an attempt" at MPT; as it
may, in fact, not even achieve anything more than Mediocre Power
Transfer. After peaking the grid and dipping the plate, I have
observed many different peaks and dips for many various loads to know
that not all loads obtained all available power.

The classic description of a tune-up is based on qualitative
assumptions and the amplifier is brought into its best attempt, which
is not demonstrably efficient, nor even proven to be "matched"
conjugately or by impedance. This takes more information (so far
unrevealed) obtained by current into the known load (unrevealed), and
power into the source (unrevealed). No one other than myself has
expressed the loss of the source because no one else has ever
enumerated its resistance (a topic commonly hedged and avoided) Hence
discussion of efficiency is lost in the woods and correlation to
MPT/Z/Conjugation is equally doomed to ambiguity.

Are you serious? As I understand Everitt's statement of

Everitt notwithstanding, Lord Kelvin trumps him with
"when you cannot express it in numbers, your knowledge is of a
meagre and unsatisfactory kind"
This thread has suffered from a lack of measurables that are not that
difficult to obtain.

Richard, are you inferring that I have not submitted the measurables required to
determine the source impedances of the xmtrs I measured? What additional
measureables that I haven't already submitted are you asking for to prove the
source impedances that I've already submitted are valid?

So, to return to my very specific question:
What is the source resistance of any power amplifier?

Richard, the source impedance of one of the xmtrs I measured with load impedance
of 17.98 + j8.77 ohms measured 18 - j8 ohms. Considering measurement error,
wouldn't you agree that these two impedances qualify for a conjugate match, and
that this value of source impedance is valid at least within the realm of
possibility?

For any match?

One complex number is sufficient, and certainly that value will
resolve all imponderabilities is what I am asking for.

OK, Richard, is impedance 18 - j8 ohms sufficient?

Richard Clark, KB7QHC

Walt,W2DU