Hi OM,

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

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.

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%.

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.

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 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. Their utility
follow theory, they do not drive theory.

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 (?). 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.

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.

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.

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

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? Such
nebulous thinking clouds the obvious observation that the full range
of devices themselves operate on only one principle. What is limited
is the human component of their perception, not the physical reality
of their operation. 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.

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.

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.

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.

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

I rejected it as an unnecessary filigree, 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.

....But not really. I have little faith that the difference is
appreciated nor how many ways a match may be accomplished or for what
ends.

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

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 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.

73's
Richard Clark, KB7QHC

Asimov wrote:
In fact the power difference is
always zero, so there is no reason for the device to cool.

Here's the reason the device cools under load.

Plate loss = Eb*Ib - Ip^2*RL

With no signal, the plate loss is Eb*Ib. When
the signal is increased from zero, any power
delivered to the load is subtracted from Eb*Ib,
thus causing the device to cool.
--
73, Cecil http://www.qsl.net/w5dxp


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

One would think that a 12 billion year windowing
would be close enough. :-)
--
73, Cecil http://www.qsl.net/w5dxp


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Asimov wrote:
harmonic generation...

Why do the instructions on my stereo amp warn against
running the amp with no speakers attached?
--
73, Cecil http://www.qsl.net/w5dxp


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I read in sci.electronics.design that Cecil Moore
wrote (in ) about '1/4 vs 1/2 wavelength
antenna', on Wed, 2 Mar 2005:
Richard Clark wrote:
There are no sine waves in nature, so by this contortion of logic from
above there are no s-domains (?). 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.

One would think that a 12 billion year windowing
would be close enough. :-)

Not only that, but since by definition the Universe started at T=0, any
'sine wave' that starts at a positive zero-crossing is at any later time
indistinguishable from a real one that started at T=0.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Asimov wrote:
"Let`s look at it from the dynamic point of view (loss in a Class A
amplifier)."

The no-signal loss of a Class A amplifier is 100%. It equals volts x
amps and appears in the amplifier. Now feed a signal to the ideal
amplifier set just below the clipping level. Average d-c power is
unchanged from the unloaded and no-signal conditions.

Connect a matched load resistor to the amplifier output. If physically
small, the resistor may become warm with heat that were it not for the
load would be otherwise dissipated in the amplifier. Input power to the
Class A amplifier is unchanging.

Finding the internal resistance theoretically is simple. It is simply
the open-circuit output voltage divided by the short-circuit current.

Open-circuit voltage at full output and short-circuit current may be
severe. Internal resistance can be found under less stressful
conditions. Internal resistance will drop the voltage to any load
reasistance. Use the voltage-divider formula to calculate the internal
resistance.

With pure resistances, half the open-circuit volts are dropped by the
internal resistance when the load is a match.

A power amplifier`s internal impedance can be determined.

Power output from a Class A amplifier cools it.

Best regards, Richard Harrison, KB5WZI

"Cecil Moore" bravely wrote to "All" (02 Mar 05 07:55:04)
--- on the heady topic of " Say what you mean."

CM From: Cecil Moore
CM Xref: aeinews rec.radio.amateur.antenna:26244

CM Asimov wrote:
harmonic generation...

CM Why do the instructions on my stereo amp warn against
CM running the amp with no speakers attached?

Because then the screen tries to carry the plate signal, the reactance
in the output transformer is not damped, and because a tube is
sensitive to voltage, this quickly leads to a molten hole in the side?
Watts to plasma.

A*s*i*m*o*v

Ken Smith wrote:


The strongest argument for dropping the impedance matching concept is PA
efficiency, and therefore maximum signal swing. Obtaining maximum swing is a
load line issue.

What do you mean by "maximum signal swing" in this context. I can get a
bigger swing by leaving the output completely unloaded and hence causing
the actual efficiency to be zero.

LOL. Sure, the purpose of a power amp is to actually extract power. This is a
good start.

Perhaps a simplistic (and of course idealized) class A example would help. And
I want to remind that this is a simplification of the first order design cut.

The first assumption/idealization for the class A example would be to demarcate
between strong and weak non-linearity. This demarcation is basically the
boundary of clipping, both positive and negative. That is, we want our class A
amp to swing to the rails but not go beyond. In our class A design we will
accept weak non-linearity but not strong non-linearity.

Lets say we have selected a class A device/amplifier for which we can statically
dissipate 10W. The drain DC circuit is simply an RF choke (see, it is a simple
example!). Let's say the quiescent values are a 10 V supply and 1 A of current
(10 W). The question is: how do we load the device to extract maximum power
given the "no clipping" (strong non-linearity) constraint?

Say we load it with 20 ohms, what happens? The max positive swing before
clipping is Id*rL = 1*20 = 20 V. The max negative swing is, of course, Vd = 10
V. Since the 10 V is the lesser of the two swings, our non-clipping design
constraint limits us to 20 Vp-p. So we can deliver (Vp)^2/(2*rL) =
(10)^2/(2*20) = 2.5 W.

Say we load it with 5 ohms, what happens? The max positive swing before
clipping is Id*rL = 1*5 = 5 V. The max negative swing is, of course, Vd = 10
V. Since the 5 V is the lesser of the two swings, our non-clipping design
constraint limits us to 10 Vp-p. So we can deliver (Vp)^2/(2*rL) = (5)^2/(2*5)
= 2.5 W.

Say we load it with 10 ohms, what happens? The max positive swing before
clipping is Id*rL = 1*10 = 10 V. The max negative swing is, of course, Vd = 10
V. Since they are equal, we get 20 V of p-p swing. So we can deliver
(Vp)^2/(2*rL) = (10)^2/(2*10) = 5 W.

Our circuit loaded with 10 ohms delivers twice as much power as with the lesser
5 ohms or greater 20 ohms. That is, extracted output power is peaking at some
finite non-zero value. This is also easily seen to be most efficient point for
this simplistic example.

In no way was the ouput-Z of the amplifier considered in deciding how to load it
for the purpose of extracting maximum power from the circuit. The output-R is
completely irrelevent.

This example is intended to be illustrative rather than exact.

The reactive component issue is still there too. Reactive loads cause
increased currents in the output stage without delivering any power to the
load so they still need to be reduced as much as practical.

Yes, I already noted that for that portion of the impedance, it should be tuned
out *as best* possible.

"...(to be fair, the time-averaged reactive output component is tuned out as
best possible)."

Richard Clark wrote:

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

It is about DC to RF efficiency,

Put a number to it.

as I've been pointing out since my
first post, and which you initially commented was "nonsense"

Hi OM,

And so it remains with additional elaborations not quoted here.

but now seem to agree with.

Seeming is a rather insubstantial thing to hang your theories on.

Well they are apparently your's too! Your own example of testing your own PA
said absolutely zip about output-Z. The most you could say is how the circuit
is loaded and its RF/DC efficiency. You're agreeing with me and can't even seem
to recognize it.

"Impedance matching" meant in the normal sense of conjugate
matching for maximum transfer of power

And this reveals the error of "Seeming" because the so-called meaning
you ascribe is this same nonsense.

Here's the original quote [Ken]:

"When the correct matching is done, the antenna works as an impedance mathcing
network that matches the output stages impedance to the radiation resistance."

He brought up "matching to the output impedance" (of the device), not me. There
is no "misinterpretation of meaning" when it comes to making statements about
matching output impedance to a load impedance. The meaning is well-understood
and precise. It means conjugate matching for maximum power transfer, and this
is explicitly sourced from small signal theory. Small signal theory is
oblivious to practical factors like supply rails and efficiency. These
practical factors are paramount in PA design. Thus to apply a theory that
ignores paramount factors is to beg a design which will likely be non-optimal.

Pay more attention to reading
instead of writing.

I'm paying attention, you agree with me but don't have the background to
understand it.

It has been pointed out more than once, and by
several, that Matching comes under many headings. The most frequent
violation is the mixing of concepts and specifications (your text is
littered with such clashes).

No, you still don't get it. I don't have a problem with saying it is
"matched." For example, I said a PA needs to be "load-line matched." This has
a specific meaning, and that meaning explicitly isn't "impedanced matched,"
which means something else. If you don't bother to know what the words mean, I
might as well speak Swahili.

is a misapplied small signal
concept/model. I think that is all I've really been saying.

And I preserved this clash quoted above as an example. If there is
any misapplication, you brought it to the table with this forced
presumption.

There is no forced presumption. The words have explicit definitions. If you
don't know the language, you have no way of communicating.

The misapplication of S parameters to a large signal
amplifier is one thing, to project this error backwards into the
fictive theory that there is some difference between large and small
signal BEHAVIOR (not modeling) is tailoring the argument to suit a
poorly framed thesis.

The models come from behavior and/or device physics, and were developed for the
express purpose of efficient design methodology. Small signal models can (and
do) conveniently ignore large signal concerns such as efficiency and supply
rails, because such concerns are irrelevent in the small signal milieu. To
apply a model to a milieu for which the model is not suited begs a non-optimal
design. The output-impedance concept itself is quite dubious for large signal
amplifiers.

None of your dissertation reveals any practical substantiation, hence
it falls into the realm of armchair theory. We get plenty of that
embroidered with photonic wave theory that is far more amusing.

You are off track.

I read in sci.electronics.design that gwhite wrote
(in ) about '1/4 vs 1/2 wavelength
antenna', on Wed, 2 Mar 2005:

I might as well speak Swahili.


Good idea! Furahini mkaimbe. The wrangling is getting tiresome.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk