1/4 vs 1/2 wavelength antenna

Still here, not quite sure who to believe, but enjoying the ride

 

[keith]

On Sun, 27 Feb 2005 17:12:46 +0000, Ken Smith wrote:

In article <CVcFzUAFBXICFwjZ@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
[...]
If the FM is what passes for music these days, it's MUCH better IMHO.

There is very little that is sent in the form of radio waves that is worth
the electrical power to send it.

Hmm, many advertisers would disagree. Since they have real money at stake
and you don't...

The really sad thing is that much of
what is send via FM is really "voice grade" material. When FM was new,
the material for FM was specially produced to take advantage of the wide
bandwidth and large dynamic range.

Bandwidth, perhaps. Wide dynamic range? The FCC rules seem to
suggest otherwise.

--
Keith

 

[Richard Clark]

On 27 Feb 2005 18:05:36 -0800, yahdjt@bigfoot.com wrote:

Still here, not quite sure who to believe, but enjoying the ride

Hi OM,

The long and short of it (apropos of your antenna spec), is that your
shorter antenna will need a new matching circuit (apropos of the
smaller antenna's size) for the related issues of maximum transfer of
power. The reasons for matching may vary (and with it, efficiency),
but not so you would notice. If you did notice, then your production
tolerance (if not customer application) variations will kill you in
the marketplace (fact of life in a Kapitalistic world). No amount of
armchair philosophies about Thevenin's theorem will replace that loss.

73's
Richard Clark, KB7QHC

 

[Jim Kelley]

Rich Grise wrote:

No, just trying to make the point that it does, in fact, _have_ an
impedance. (even if it's running class E.) What that exact impedance is,
of course, is left as an exercise for the reader.

And like any impedance, is a function of frequency.

And another thing - in a transmitter, the impedance matching only happens
at the one frequency, which is a lot different scenario from, say, a
stereo. This could be a confusion factor here.

There may be more similarity than difference over the respective 20 KHz
bandwidth.

ac6xg

 

[gwhite]

Richard Clark wrote:

No amount of armchair philosophies about
Thevenin's theorem will replace that loss.

Thevenin's is a linear theorem. Large signal devices are not linear. (Hey,
maybe triodes are, but I don't use them for PA's.)

There is no armchair philosophy about Thevenin's theorem because it does not
apply in the RF PA situation. Your's is a red herring.

 

[Wes Stewart]

On Fri, 25 Feb 2005 22:56:47 -0600, Cecil Moore <w5dxp@hotmail.com>
wrote:

Ken Smith wrote:
If you then
put in the output device protection they didn't include, you end up with
the matching as I explained elsewhere.

SWR foldback is part of impedance matching?

It is in the sense that it improves the source match by trying to hold
the forward power constant regardless of load. Most SWR foldback
systems overreact but a good ALC system, what we called a "leveling
loop" in waveguide reflectometers back in the mid-20th century
certainly improve the source match.

 

[Richard Clark]

On Tue, 01 Mar 2005 18:06:18 GMT, gwhite <gwhite@deadend.com> 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.

"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. Pay more attention to reading
instead of writing. 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).

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. 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.

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.

73's
Richard Clark, KB7QHC

 

[Ken Smith]

In article <4224AF38.770053D4@deadend.com>, gwhite <gwhite@deadend.com> 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.
Any change in the load, no matter how small, will cause a change in the
output voltage and the output current. 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.


--
--
kensmith@rahul.net forging knowledge

 

[John Woodgate]

I read in sci.electronics.design that Ken Smith
<kensmith@green.rahul.net> wrote (in <d039qq$uq5$4@blue.rahul.net&gt
about '1/4 vs 1/2 wavelength antenna', on Wed, 2 Mar 2005:

In article <4224AF38.770053D4@deadend.com>, gwhite <gwhite@deadend.com> 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.
Any change in the load, no matter how small, will cause a change in the
output voltage and the output current. 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.


This incremental impedance is one of several different impedances that

can be defined for a non-linear source. No one is more valid
conceptually than another, but some are of more practical significance
than others.

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.
--
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

 

[Cecil Moore]

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


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[John Woodgate]

I read in sci.electronics.design that Cecil Moore <w5dxp@hotmail.com>
wrote (in <4225c50a$1_2@127.0.0.1&gt 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

 

[John Woodgate]

I read in sci.electronics.design that gwhite <gwhite@deadend.com> wrote
(in <42260EDB.BB0D03AB@deadend.com&gt 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

 

[gwhite]

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 <gwhite@deadend.com> 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/detail/-/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/detail/-/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 ćther. 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]

I read in sci.electronics.design that gwhite <gwhite@deadend.com> wrote
(in <4226274C.2701686E@deadend.com&gt 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

 

[gwhite]

John Woodgate wrote:

I read in sci.electronics.design that gwhite <gwhite@deadend.com> wrote
(in <4226274C.2701686E@deadend.com&gt 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.

 

[gwhite]

Ken Smith wrote:

In article <4224AF38.770053D4@deadend.com>, gwhite <gwhite@deadend.com> 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/detail/-/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

 

[Ken Smith]

In article <4226056F.48E4AF54@deadend.com>, gwhite <gwhite@deadend.com> 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.


--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <42260EDB.BB0D03AB@deadend.com>, gwhite <gwhite@deadend.com> wrote:
[...]

:

"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.



--
--
kensmith@rahul.net forging knowledge

 

[gwhite]

Ken Smith wrote:

In article <4226056F.48E4AF54@deadend.com>, gwhite <gwhite@deadend.com> 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.

Well really, once the device and supply have been determined, we can indeed view
it as extraction. We'll load it to extract the most. If you want to mince
words and call it "deliver," that is fine.

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.

Well, class A is certainly done. Two cases are where the extra little bit of
linearity is desired and at high frequencies, were PAE starts to take a bite as
the gain drops below 10 dB.

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.

No, this is exactly where I'm saying you are incorrect. You are not getting the
practical limitations and are mistakenly applying linear concepts. It doesn't
work if you want to extract maximum power from the DC supply through a real
device, converting the DC power into RF power.

 

[gwhite]

Ken Smith wrote:

In article <42260EDB.BB0D03AB@deadend.com>, gwhite <gwhite@deadend.com> 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.

Driven to max swing, this is true. But it is because of asymmetrical clipping,
not because of conjugate mismatch. For lower drives, what you say won't
necessarily be true *unless* you've mis-designed according to conjugate match
ideals. Your argument is circular.

If you design for conjugate match, you're right. I'm saying: don't do that. If
I design for load line match and you design for conjugate max (both pf us using
the same device and supply), I will get a higher peak power than you will.
However, you'll get to be right about how your amp acts regarding diverging from
conjugate load. But it is irrelevent: you made a fundamental mistake.

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.