Richard Clark wrote:

Hi OM,

This goes into the intricacies of how forced propositions do not yield
a forceful argument.

LOL.

On Tue, 01 Mar 2005 18:06:18 GMT, gwhite wrote:

You don't know the output impedance because you
don't have a way of determining it by swinging the output full-scale.

This is more properly an admission from you, than a projected
inability upon us. You may not know how, but this does not prevent me
from expressing a value that is suitably accurate.

Now, within the field of measurement, no statement is accurate without
an expression of its range of error. However, in this regard accuracy
is still a remote issue as you offer nothing of practical
consideration and have failed to respond to a simple example to
provide context.

Sheesh!

Richard Harrison, , KB5WZI, has in this sense already done the heavy
lifting with:
From the specifications page also, the power reguirement is TX: 18A
13.8V DC. It`s a linear amplifier. Only 40% efficiency. The designer
probably was more interested in low harmonics than efficiency. The final
by itself only takes part of the 18A ao its efficiency is more than 40%.

Efficiency seems to be important enough to mention.

continuing....

Even for class A, large signals will/can have rail to rail swing.

This marks an artificial imposition not required to respond to the
spirit of the topic. Such swings are not necessary.

No one said they "are necessary." But not driving "as hard as possible" simply
means you are wasting power and paying for a bigger device than you need to.

The device will not be
linear for large swings: sinusoidal input swing will not result in a sinusoidal
output swing.

This is immaterial to impedance,...

Oh? The definition of impedance is:

Z = V/I

V and I are sinusoid (phasors), *by definition*. It is as if you don't know the
definition of impedance.

and is a set-up of another artificial
imposition: the Thevenin Model (which was specifically dismissed).
Hence we are into a cascade of impositions.

But "impedance" is a sinusoidal (s-domain) concept.

This is baloney cut thick. S Domains (?) are at best a modern
contrivance to model well behaved small signal devices.

S-domain *is* linear circuit theory.

Their utility
follow theory, they do not drive theory.

It *is* linear circuit theory. The theory was developed for its utility.

http://www.amazon.com/exec/obidos/tg.../-/0801869099/

So how can
you define an impedance--a sinusoidal concept--when the waveform is not
sinusoidal for an inputted sine wave?

There are no sine waves in nature, so by this contortion of logic from
above there are no s-domains (?).

What are you talking about? No circuit is perfectly linear, and no one I knows
claims such. That does not invalidate linear theory, nor denigrate its utility
properly applied. Many circuits are "sufficiently linear," and "care" little
about supply rails and efficiency.

Why are there no sine waves in
nature? Because nature is bounded by the Big Bang (a discontinuity)
at one end, and has yet to fulfill its infinite extent.

I'm not religious, but you beg me.

Ohmigod!

In other words, tedious appeals to artificial impositions of purity
fail at the gate for their sheer collapse of internal logic. This
kind of stuff appeals to arm-chair theorists who find themselves
impotent to perform.

Suit yourself. Go ahead and apply theory to that for which it was not designed
to handle. In fact, you don't do it -- your own example about testing your PA
stated absolutely nothing about linear theory, or output impedance of the
device. I use (apply) linear theory a good share of the time. That doesn't
mean I don't recognize its limitations as a theory (a model).

The point is that the output impedance is
time dependent ("causes" the non-sinusoid output for sinusoid drive), which
rather makes the concept questionable. As I wrote earlier, one might decide to
consider a time averaged impedance, but I'm not clear on what the utility would
be.

Classic performance anxiety. Engineers learn to live with limitation
and to express results and sources of error so that others can judge
merit. Priests are better suited with mulling over these issues of
ambiguity.

Wow. More importantly, engineers select appropriate models for the design
task. They don't bother with ones that have no application to the task at hand.

There is no "presumption." Linear parameters and theorems totally ignore
practical limitations--this is a fact and you can look it up in just about any
text on circuit analysis.

Knowledge limited. There are many suitable texts that offer a wider
spectrum of discussion that are fully capable of answering these
issues.

Yeah, like for example:

http://www.amazon.com/exec/obidos/tg.../-/0890069891/

However, it is made worse that most of this stuff is
derivable from first principles and no recourse to vaster libraries is
actually needed.

Yes, load line matching is certainly a first principle.

The simple linear model is perfectly okay for small
signal devices. It isn't okay for large signal devices.

And yet there is no substantive illustration to prove this ambiguous
point. What constitutes small, and what demarcates large?

Maybe you didn't read those first principles quite closely enough. Nor have you
read this thread well. Large signal amplifiers -- i.e. power amplifiers --
"care" about DC to RF efficiency and supply rails. Small signal amplifiers
don't "care" about that.

Such nebulous thinking clouds the
obvious observation that the full range
of devices themselves operate on only one principle.

Quite afraid to ask, but being brave, I ask: what "one principle" is it "that
the full range of devices themselves operate" upon?

What is limited
is the human component of their perception, not the physical reality
of their operation.

And you critiqued me for nonsense.

The faulty choice of models (S Parameters) is not
the fault of either Physics or the devices when they diverge from the
crutch of calculation against the wrong mathematical expression.

And no one said so.

In any case, load pull
equipment does not make the pretense of defining output impedance of an active
large signal device. It does say what the load needs to be to acquire maximum
power out of the device.

This is simply the statement from a lack of experience.

No, it is a fact of the matter. You don't know what the equipment does.

Thevenins and conjugate matching (for maximum power transfer) are
explicitly linear small signal device models. Their use in RF PA output design
is a misapplication.

These statements are drawn from thin air.

No, for PA design, the thevenin impedance of the output source never enters "the
equation." Thus pretending that it "is there" is an unfounded assertion. You
asserted thevenins to PA design, now prove it. You can't.

So to return to a common question that seems to defy 2 out of 3
analysis (and many demurred along the way) - A simple test of a
practical situation with a practical Amateur grade transistor model
100W transmitter commonly available for more than 20-30 years now:
1. Presuming CW mode into a "matched load" (any definition will do);

Any definition won't do, and for this discussion the specific "won't do" is
using conjugate matching which is a small signal (linear) model.

Given the failure to provide any discussion for either or any form of
matching suggests a lack fluency in any of them.

What utter ignorance of what has actually been written. In my very first post I
described the first order cut of matching technique.

*You* brought up Thevenins and armchair philosophy regarding it, not me.

I rejected it as an unnecessary filigree,...

Exactly. It is not necessary. But you brought it up, and Ken implied a simile
with "impedance matching." You might wonder why it is not necessary. You might
even ask the question wondering if the reason it never shows up is because it
would be a misapplication of the concept.

... but I notice in the quotes
above that you readily embraced it as a necessary imposition.

I said
Thevenins was irrelevent, and now you appear to agree with me. Ken effectively
brought up conjugate matching, not me.

This compounded with the denial of Thevenin is quickly closing the
available matching mechanisms. If it is not about Thevenin, and it is
not about Conjugation, then I am willing to wait to hear what it IS
about.

Ah, at last a relevent question/statement. See my first post in this thread.

...But not really. I have little faith that the difference is
appreciated,...

You don't appreciate it because you don't understand it. That's not my problem.

nor how many ways a match may be accomplished or for what
ends.

If you don't know what the end is for an RF PA, how could you hope to scratch a
meaningful and optimal solution?

The original comment I was challenging
was:

"...the antenna works as an impedance mathcing network that matches the output
stages impedance to the radiation resistance."

I am always suspicious of how a quoted claim is couched by the
rebutter (cut and paste from the original is always available and
citing the link to the complete contextual post is hardly Herculean).

LOL. I guess you don't appreciate convenience.

However, responding to the bald statement, I find nothing
objectionable about it.

That's because you don't understand the difference between impedance matching
and ac load line matching.

I simply wanted to make it clear that the "matching" done was not an issue of
"output impedance" per se. It is an issue of how the transistor is to be loaded
to extract maximum ouput power.

Again, a presumption not brought to the table.

It was brought to the table in my first post to this thread.

It may follow as a
consequence, but it is not a necessary condition.

Our questioner who started this thread is undoubtedly interested in
the outcome in terms of maximum radiation for a limited power - it is
a chain of causality that is a forced step matching issue from the
battery to the æther. This is a first principle of successful
production engineering.

How would you know about first principles of production engineering and what
does it have to do with this thread?