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?

On Wed, 02 Mar 2005 20:30:45 GMT, gwhite wrote:

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.


Mmm-Hmm

On Wed, 23 Feb 2005 19:08:20 GMT, gwhite wrote:

RF transmitters are not impedance matched to antennae in the sense of maximum
transfer of power.

Hi OM,

As I've noted in the past, you can fill a library with negative
assertions without ever offering an answer, eg.:
RF transmitters are not Nuclear resonated to antennae in the sense of maximum
transfer of power.

RF transmitters are not impedance matched to antennae in the sense of maximum
balance of payments.

RF transmitters are not cosmically matched to antennae in the sense of maximum
psychrotropic power.

The list could go on, be completely accurate, and yet never actually
mean anything in the end much as the nonsense you offered from the
start.

You sighed with content at being offered a "relevent
question/statement" Your re-iterative response contains the same (how
could it be otherwise?) slack of precision that started this. Want to
try again?

You could have as easily expressed what sense they ARE matched, but
instead this time offer what Basis of Matching you are attempting to
describe. This is the more rigorous approach that eliminates vague
descriptions and uses standard terms. If you have to query about what
"Basis" means (used by professionals - namely metrologists who can
quantify Output Z of all sources) - then we can skip it as a topic out
of the reach of amateur discussion.

Note:
Again, RF PA's should be load-line matched.
Does not qualify as a Basis. It is suggestive of one, but because you
indiscriminately mix several Basis within your discussions, it is your
responsibility to be precise. If you can accomplish this, then we can
proceed to review how little it all matters.

Barring resolving any of these issues of precise language, I notice
that you rather enjoy fruitless jousting with them than challenging my
support of Ken's (supposed) statement that you say is your focus:
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.
We will leave that as another dead-end.

73's
Richard Clark, KB7QHC

Richard Clark wrote:


As I've noted in the past, you can fill a library with negative
assertions...

The troublesome assertion is not the negative one. It is that RF PA's are
conjugate matched. Neither you nor Ken has provided a single example of such a
design that also extracts the maximum amount of "linear" power from a device and
essentially its power supply (after all, that is what it is: a _power_ amp).
Your example said nothing about output-Z, which suggests you have no clue, since
you didn't even remotely address the issue.

For Ken's part, he recently obfuscated by dismissing an example that was
primarily intended to be illustrative, but yet holding the salient points. He
completely ignored (or didn't understand) the clipping issue. Further
obfuscation was provided by talking about "protection circuitry," which may or
may not exist in a circuit, but adds zero to a discussion regarding how the PA
is to be loaded. "Protection" is a non-stater because the PA is either off or
impaired.

Ken's argument is circular. He say's that if a design is done for conjugate
match,
then it will behave as if it is conjugately matched. Well of course (or at
least sort of under specific test conditions and circuits)! It is
self-fullfilling prophecy but it unfortunately makes no statement regarding
obtaining the maximum power out of the circuit in the sense of turning DC power
into RF power (yes, *extracting* power from the DC supply and transformed to
RF). This is paramount to PA design. To use the device to maximum efficacy, as
Cripps puts it, a load-line match is needed. Ken's "conjugate match" design
won't do that, and that's why PA's aren't designed that way.

The bottom line is that if I design an amp via load line techniques using the
same device and power supply as Ken (him using conj-match), my amp will deliver
higher unclipped PEP than his. That is the factual result you resist. Now if
you want to pay for extra power and big devices, that's your business--go ahead
and attempt to conj-match your amp--but engineers who design PA's don't do that.

Another idealized and hypothetical example to elucidate the load-line principle
is offered.

Let's say we have a 10 W FET we'll build into a class A circuit. An RF choke is
used to supply drain current. We DC bias it to Vd = 10 V and Id = 1 A. Just
for argument sake, let's say it has a constant internal resistance of 110 ohms
and the device will break down at 25 V. According to the most idealized and
standard load-line theory, we should load it to rL = Vd/Id = 10 Ohms. This
idealization includes the definition of positive and negative clipping --
whichever comes "first" -- of being the operational limit for output voltage
swing. Clipping is associated with severe distortion.

Since we need rL to be 10 ohms, and Ri = 110 ohms, we need to make the actual
load resistor equal to: RL = 11 Ohms. Let's check that result and see if it
meets the clipping constraint for maximum available power.

positive swing = Id*rL = 1*10 = 10 V
negative swing = Vd = 10 V
Power delivered to RL: Pload = 10^2/(2*11) = 4.55 W
The efficiency is a little under 50% because of the internal resistance. Note
the Load resistance is decidely not the conjugate of the internal resistance.

Let's spot check the load to see if it at least appears to be the peak available
power, by testing two loads "immediately" on either side of our optimum 11 ohms.

Let RL = 10 ohms
positive swing = Id*rL = 1*9.17 = 9.17 V
negative swing = Vd = 10 V
Since we positive clip at 9.17 V, we are limited by our design clipping
constraint to only driving the PA such that 2*9.17 V is the maximum available
voltage swing.
Power delivered to RL: Pload = 9.17^2/(2*10) = 4.20 W

Let RL = 12 ohms
positive swing = Id*rL = 1*10.82 = 10.82 V
negative swing = Vd = 10 V
Since we negative clip at 10 V, we are limited by our design clipping constraint
to driving the PA such that 2*10 V is the maximum available voltage swing.
Power delivered to RL: Pload = 10^2/(2*12) = 4.17 W

Sure enough, the power peaked at a load of 11 ohms, just like load-line theory
says it will. Now let's see what the available power hit of conjugate matching
is.

By definition, conj-match insists RL = Ri = 110 ohms. Again we are limited in
our clipping constraint by static drain current, and supply voltage,
specifically 10 V.

Our negative swing limit is, as ever, 10 V (the drain voltage).

positive swing = Id*rL = 1*55 = 55 V

This would breakdown the device, but the lower negative swing will force us to
back down the drive to meet the design defined clipping constraint.

Pload = 10^2/(2*110) = 0.455 W

Conjugate matching resulted in a 10*log(0.455/4.55) = 10 dB available power
hit. Power amplifiers are not designed with conjugate matching in mind. You
don't need to re-invent the wheel. Just follow well established principles when
doing cookie cutter PA design.

The list could go on,...

LOL. Given your pattern, I am sure it will.

You sighed with content at being offered a "relevent
question/statement" Your re-iterative response contains the same (how
could it be otherwise?) slack of precision that started this. Want to
try again?

Not really. The problem isn't precision, it is you can't, or refuse, to
comprehend what is being said, which I presume is why you instead write with the
most bizarre terms and phrasology that has nothing of import to the topic at
hand.

You could have as easily expressed what sense they ARE matched,

For what seems like the billionth time now: they are load-line matched.

...but instead this time offer what Basis
of Matching you are attempting to
describe.

I've given a didactic example (actually a couple), you just don't--or more
likely won't--get it. If you don't like my example, you can refer to Cripps,
who is considered one of the preeminant RF PA experts in the world.

Even more simplistic is Malvino's discussion on pp177-185 of the first edition
((c) 1968) of "Transistor Circuit Approximations." It is basically a technician
level description, so perhaps it is well-suited to you. In academics, load-line
theory is presented down to tech level courses and up across to engineering.
That some engineers and techs aren't clear on the load-line concept for PA's (or
*any* circuit needing a wide symmetrical swing) is notwithstanding.

This is the more rigorous approach that eliminates vague
descriptions and uses standard terms. If you have to query about what
"Basis" means (used by professionals - namely metrologists who can
quantify Output Z of all sources) - then we can skip it as a topic out
of the reach of amateur discussion.

I see you still don't know what impedance is. In any case, it doesn't mean that
looking into a properly designed PA output with a network analyzer confirms the
conj-match precept, it doesn't.

Impedance is a *linear* conception, a portion of linear theory, and again by
definition:

Z = V/I

V and I are sinusoids (phasors). But with power amps, substantial non-linearity
exists (destroying the linearity assumption of impedance), thus applying a
linearly defined concept to a non-linear milieu is a misapplication. You are
attempting, as is Ken, to stuff a square peg down a round hole. Why?

The concept is even questionable for the most linear of the power amps: class
A. In any case, given real devices with real supplies, the conj-match ideal is
next to worthless. While I could agree that the borderline may be fuzzy
regarding where and when to drop the impedance notion, it still stands that the
concept is not useful in determining how to optimally load an RF PA.

At this point you own the conj-match assertion as much as Ken. Prove it! You
can't because it is fundamentally incorrect.

Note:
Again, RF PA's should be load-line matched.
Does not qualify as a Basis.

Load-line matching is such a basic electronic concept it is unbelievable how
oblivious you are to the concept. Read a basic book. Don't rely on me: look it
up and do your own design!

It is suggestive of one, but because you indiscriminately
mix several Basis within your discussions, it is your
responsibility to be precise.

You just like to hear yourself talk. I've been explicit and precise. You just
don't know anything about the elementary electronics principle of load line
matching. I presume this is why your comments have zero substantive
responsiveness.

If you can accomplish this, then we can
proceed to review how little it all matters.

If you keep ignoring what I've written, and that which is written in elementary
electronics texts, you can remain happily ignorant of understanding the
simple-basic-fundamental concept presented. Your choice.

Barring resolving any of these issues of precise language,...]

The guy ignorant of the definition of impedance and that s-domain theory *is*
linear circuit theory (and more goodies) is talking about "precise language."
Amusing.

I notice
that you rather enjoy...

No, I don't enjoy it at all. Your lack of electronic understanding is dismal,
especially given your tone. It would have been a lot easier for me if Ken
hadn't made the erroneous
statement in the first place and made a correct one instead. That would have
been my preferance.

..fruitless jousting with them than challenging my
support of Ken's (supposed) statement that you say is your focus:
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.
We will leave that as another dead-end.

I suspect you will. I already understand it -- you're the one who doesn't.


"One of the principal differences between linear RF amplifier design and PA
design is that, for optimum power, the output of the device is not presented
with the impedance required for a linear conjugate match. That causes much
consternation and has been the subject of extensive controversy about the
meaning and nature of conjugate matching. It is necessary, therefore, to swallow
that apparently unpalatable result as early as possible (Section 1.5), before
going on to give it more extended interpretation and analysis (Chapter 2)." --
Cripps, p1


The quote is on Page 1. Swallow it now. Learn something for a change.

I read in sci.electronics.design that gwhite wrote
(in ) about '1/4 vs 1/2 wavelength
antenna', on Thu, 3 Mar 2005:
By definition, conj-match insists RL = Ri = 110 ohms. Again we are
limited in our clipping constraint by static drain current, and supply
voltage, specifically 10 V.

Our negative swing limit is, as ever, 10 V (the drain voltage).

positive swing = Id*rL = 1*55 = 55 V

This would breakdown the device, but the lower negative swing will force
us to back down the drive to meet the design defined clipping
constraint.

Pload = 10^2/(2*110) = 0.455 W

And the power dissipated in the device is also 0.445 W. Matching
according to the 'maximum power theorem' or conjugate matching, results
in equal power in the PA and load. That's why it isn't useful for power
amplifiers.

Doesn't everyone know that an audio amplifier that id designed to feed
an 8 ohm load MUST have an output source impedance of 0.0000001 ohms or
less. An output source impedance of 8 ohms would dramatically decrease
the electromagnetic damping on the loudspeaker voice-coil - by the huge
factor of .... two!(;-)
--
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

On Thu, 3 Mar 2005 20:53:48 +0000, John Woodgate
wrote:

Doesn't everyone know that an audio amplifier that id designed to feed
an 8 ohm load MUST have an output source impedance of 0.0000001 ohms or
less.

Hi John,

I hope that was a joke.

73's
Richard Clark, KB7QHC

On Thu, 03 Mar 2005 13:44:06 -0800, Richard Clark wrote:

On Thu, 3 Mar 2005 20:53:48 +0000, John Woodgate
wrote:

Doesn't everyone know that an audio amplifier that id designed to feed
an 8 ohm load MUST have an output source impedance of 0.0000001 ohms or
less.

Hi John,

I hope that was a joke.

Please! You know Mr. Woodgate _hates_ explaining his jokes:

"Doesn't everyone know that an audio amplifier that [is] designed to feed
an 8 ohm load MUST have an output source impedance of 0.0000001 ohms or
less[?] An output source impedance of 8 ohms would dramatically decrease
the electromagnetic damping on the loudspeaker voice-coil - by the huge
factor of .... two! (;-)
[^^^^]

Please notice the last sentence in that paragraph. ;-)

73's

Best regardses? ;-)

Cheers!
Rich

Rich Grise wrote:

On Thu, 03 Mar 2005 13:44:06 -0800, Richard Clark wrote:

On Thu, 3 Mar 2005 20:53:48 +0000, John Woodgate
wrote:

Doesn't everyone know that an audio amplifier that id designed to feed
an 8 ohm load MUST have an output source impedance of 0.0000001 ohms or
less.

Hi John,

I hope that was a joke.

Please! You know Mr. Woodgate _hates_ explaining his jokes:

Mr. Clark _hates_ reading and comprehending. I forsee a clash royal.

On Thu, 03 Mar 2005 23:07:14 GMT, Rich Grise
wrote:

Please! You know Mr. Woodgate _hates_ explaining his jokes:

Hi Rich,

Some love explaining their jokes. I've gotten quite a bit of
correspondence to that matter already.

73's
Richard Clark, KB7QHC

Richard Clark wrote:

On Thu, 3 Mar 2005 20:53:48 +0000, John Woodgate
wrote:


Doesn't everyone know that an audio amplifier that id designed to feed
an 8 ohm load MUST have an output source impedance of 0.0000001 ohms or
less.


Hi John,

I hope that was a joke.

73's
Richard Clark, KB7QHC

I think he just meant that damping factor is important in an audio amp.

At least I hope that's what he meant.

He forgot to mention that for that output impedance to be relevant, you
need superconducting wire to the speakers as well as superconducting
voice coils.

tom
K0TAR

I read in sci.electronics.design that Tom Ring
wrote (in ) about '1/4 vs
1/2 wavelength antenna', on Thu, 3 Mar 2005:

He forgot to mention that for that output impedance to be relevant, you
need superconducting wire to the speakers as well as superconducting
voice coils.

See the last sentence, about the effect of an **8 ohm** source impedance
on damping.
--
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