On Wed, 02 Mar 2005 19:06:32 GMT, gwhite wrote:
but now seem to agree with.
Seeming is a rather insubstantial thing to hang your theories on.
Well they are apparently your's too!

Hi OM,

From seeming to appearances - leaps of faith are better suited for
debate at the Vatican.

The remainder, unquoted due to repetition of the same basic errors,
has already been commented upon in another posting. Oh, except the
more entertaining jousts:
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.

Mmm-hmm :-)

To be so eagerly embraced as a fellow fool! Something of the chess
equivalent of the sacrificial queen gambit.

73's
Richard Clark, KB7QHC

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?

John Woodgate wrote:

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.

Not if we were there the moment the later wave turned on. I heard that amateur
operators hate splatter. RC appears to be an exception, however.

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

Not if we were there the moment the later wave turned on. I heard that
amateur operators hate splatter. RC appears to be an exception,
however.

See 'at any later time' in my text.
--
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

John Woodgate wrote:

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

Not if we were there the moment the later wave turned on. I heard that
amateur operators hate splatter. RC appears to be an exception,
however.

See 'at any later time' in my text.


Oh yeah.

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

Ken Smith wrote:

In article , gwhite wrote:
[...]
You entirely missed the point. You don't know the output impedance because you
don't have a way of determining it by swinging the output full-scale.

You don't have to swing the output full-scale to measure the impedance.

Playing along with the idea that there is some meaningful fixed Z of the device
for large swings, yes you would have to do so to prove the concept. You would
need to prove that output Z was the same for driving 1 W into the output as for
driving 100 W into the output. I also predict that even the small signal output
Z of the power amp will not be that conjugate impedance you think it is for a
properly designed PA. (I am not making a claim that it would *never* be so for
any PA.)

Any change in the load, no matter how small, will cause a change in the
output voltage and the output current.

Likewise, a change in the output Z would do the same thing. Since you're
presuming linearity, we can include gain linearity. I.e., the gain with "-10
dB" of drive is the same as the gain with "0 dB" drive. I'll define the 0 dB
gain as associated with the 1 db compression point. Since the gain is defined
as linear (really fixed regardless of drive), and the load is fixed, something
must have "caused" the compression. A way to *model* the compression is a
changed output Z as a function of drive. While I realize this is an
unconventional view of output compression modeling, I believe it is fair, since
you are making the linear presumption. I think this is fair also because the
impedance concept is a linear/sinusoid one. Under that presumption, you've given
me license to disregard distortion.


From these you can calculate the
output impedance at the current operating point.

When a transistor is operating under large signal conditions into a tuned
load, there is still an output impedance and this impedance still
discribes what will happen for small changes in the load.

Let's do another example.

Say the device we've selected has an Imax rating of 1 amp and a generator
resistance of 100 ohms. Per standard linear theory, we do our norton model of
Igen in parallel with the 100 ohms. Under standard conjugate matching theory,
we should load it with 100 ohms.
Now with the 100 ohm load, we get a 50 V peak for Imax = 1 amp. But what if
both our DC supply and device breakdown won't allow this? We have a practical
limiting Vmax not at all included in linear theory. Due to breakdown or supply
rail concerns, we'll see our Imax quite short of the 1 amp we expect when the
device is loaded with 100 ohms. We won't be getting all the power out of it we
"expect" because of practical limitations not built into linear conjugate
matching theory.

How do we select the best load, since conjugate loading clearly does not use the
device to its full potential? We seek Ropt, or what is commonly referred to as
the load line match.

Ropt = Vmax/Imax

where Ropt Rgen, if not

(Rgen + Ropt)/(Rgen*Ropt) = Vmax/Imax


So even looking into the PA output in the small signal sense (or tweaking the
impedance as you suggest), we won't likely see Ropt = Rgen, because we are
dealing with some practical design limitations not accounted for in linear
theory.

Perhaps a couple of quotes from Cripps would be nice:

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

"The load-line match is a real-world compromise that is necessary to extract the
maximum power from RF transistors and at the same time keep the RF voltage swing
within specified limits and/or the available DC supply." p13

"A final note here concerns the nebulous and highly questionable concept of
large signal impedance. The reason for the load-line match is to accommodate the
maximum allowable current and voltage swings at the transistor output. That says
nothing about the impedance of the device, which remains the same throughout the
linear range. Once a device starts to operate in a significantly nonlinear
fashion, the apparent value of the impedances will change, but the whole concept
of impedance starts to break down as well, because the wave forms no longer are
sinusoidal." p14

In article , gwhite wrote:
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.

No, the purpose of the power amp is to deliver power, not extract it.


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.

Don't bother with the over simplified Class A case. RF power
amplification is rarely done class and and it is a digression from the
actual topic.

[...]

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.

At some point as you decrease the resistance, the output will drop to zero
as the amplifier fails or it will start to decrease in some more
controlled manner as the protection circuits take control. If we assume
the latter case, it is easy to see that the power reaches a maximum value
and then decreases as the resistance is lowered. The point at which the
power is at the maximum is the point at which the load is matched. If you
make a small change in the load and observe the voltage and current when
that small change is made, you will see that that is indeed the output
impedance of the amplifier. I think this is the part you are not
grasping.


--
--
forging knowledge

In article , gwhite wrote:
[...]
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."

Yes, I stand by and have just in another part of the thread once again
explained that indeed the impedance is matched. ie: If you make a small
change in the impedance in any direction the power decreases. Increasing
the resistance is the obvious one. The other three are because the
protection circuits act. The OP had a completed transmitter he was
connecting to a length of wire.



--
--
forging knowledge

In article ,
John Woodgate wrote:
[...]
The point is that if you want to talk/write about one of these
impedances, you need, to prevent misunderstanding, use a precise term,
such as 'incremental output source impedance' and define it.

You are right. I really needed to be more clear in the first posting I
did. That bridge has now been crossed and this is getting tiresome. If
the OP doesn't come in with more questions, I'm out of here.

--
--
forging knowledge