K7ITM wrote:
But if the goal is to deliver as much clean RF power to the external
load as you can, why would you put an RF-dissipating resistor into
your amplifier?

That's the first amplifier that is taught in EE 202.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote in news:IUfQh.24090$uo3.16335
@newssvr14.news.prodigy.net:

That's the first amplifier that is taught in EE 202.

I missed the relevance of the class A amplifier.

The example that I worked up in the original post was for a design anode
load of 1400 ohms, using a practical PI coupler to a 50 ohm external load.
It is theoretical treatment of the kind of coupler circuit that you would
expect to be in the transmitter for which Walt reported his detailed
measurements.

Owen

On Apr 2, 3:58 pm, Cecil Moore wrote:
K7ITM wrote:
But if the goal is to deliver as much clean RF power to the external
load as you can, why would you put an RF-dissipating resistor into
your amplifier?

That's the first amplifier that is taught in EE 202.
--
73, Cecil http://www.w5dxp.com


You haven't moved beyond that "first amplifier that is taught in EE
202"?

If your goal is to deliver as much clean RF power to the external load
as you can, why would you put an RF-dissipating resistor into your
amplifier?

Cheers,
Tom

K7ITM wrote:
You haven't moved beyond that "first amplifier that is taught in EE
202"?

If one can understand the simple amplifier then one
can move on to a more complicated amplifier.

If your goal is to deliver as much clean RF power to the external load
as you can, why would you put an RF-dissipating resistor into your
amplifier?

My goal is not to deliver as much power as possible.
My goal is to understand the nature of the source
starting with the simplest one.
--
73, Cecil http://www.w5dxp.com

On Apr 2, 8:52 pm, Cecil Moore wrote:
My goal is to understand the nature of the source
starting with the simplest one.

Are you sure? In other threads you consistently refuse
to analyse the simplest of sources on the basis (as far
as I can tell) that it is not the 'real world'.

In light of your new approach, which I wholeheartedly
endorse, perhaps you will reconsider your response in the
other threads and try to "understand the nature of the
source starting with the simplest one".

....Keith

On Apr 2, 4:52 pm, Cecil Moore wrote:
K7ITM wrote:
You haven't moved beyond that "first amplifier that is taught in EE
202"?

If one can understand the simple amplifier then one
can move on to a more complicated amplifier.

If your goal is to deliver as much clean RF power to the external load
as you can, why would you put an RF-dissipating resistor into your
amplifier?

My goal is not to deliver as much power as possible.
My goal is to understand the nature of the source
starting with the simplest one.
--
73, Cecil http://www.w5dxp.com

If your goal "is to understand the nature of the source starting with
the simplest one," why would you add resistors you don't need and make
it more complicated than the simplest one? What if "the simplest one"
turns out to lead you into believing generalities that are not true,
when considering a more general one will avoid that?

My goal, in the context of Owen's basenote, remains to deliver as much
clean RF power to the external load as I can. Unnecessary resistors
need not apply. Matching networks better pass muster with respect to
their performance not only at fundamental frequencies, but also at
others, especially at harmonics. Not all the networks I've posted
about in this thread do pass muster, but are enlightening with respect
to Owen's observations, I believe. Simplest doesn't remain
interesting for very long.

FWIW, I don't see anything in Owen's postings in this thread that
_precludes_ a source impedance that's equal to some particular load
impedance, or to its conjugate. Rather, I see a suggestion that the
source impedance does not necessarily have to be equal to any
particular value, and in the general case does not have to be equal to
the conjugate of the design load impedance. With that I agree. I've
seen a great many examples of it. I gave a few of them earlier. I've
also worked on the design of broadband RF amplifiers which are
designed specifically to be 50 ohm resistive sources, through the use
of feedback to set that impedance. You don't need brute-force
resistors to do it; most of the time, you don't need to do it anyway,
but in the case of instruments used for measurement, it can be
important. In the case of video amplifiers where ghost-causing
reflections are to be kept to a minimum, it can be important. In the
case of a ham narrow-band SSB, CW, FSK, FM or AM transmitter, I
question whether the source impedance is ever important, or is ever
accurately known. Perhaps someone can convince me otherwise, though a
well-thought-out, well-presented example.

Cheers,
Tom

"K7ITM" wrote in news:1175574896.245112.244360
@y80g2000hsf.googlegroups.com:

On Apr 2, 4:52 pm, Cecil Moore wrote:
K7ITM wrote:
....
seen a great many examples of it. I gave a few of them earlier. I've
also worked on the design of broadband RF amplifiers which are
designed specifically to be 50 ohm resistive sources, through the use
of feedback to set that impedance. You don't need brute-force

Tom, I suggest that amplifiers with a specific equivalent source
impedance to low tolerance don't happen by accident or by magic of a PI
coupler, they require design measures that are not usually applied to
amplifiers for SSB telephony.

The assertions here that "conjugate matching" occurs naturally as a by-
product of peaking the PA is not consistent with the realities of design
of amplifiers with specific equivalent source impedance.

The amplifier configuration I used as an example was a single ended class
B valve RF linear with PI coupler for SSB telephony for comparison with
Walt's test. A push pull class B bipolar transistor amplifier with
broadband transformer coupling and high pass filter will behave
differently, and some of those designs include negative feedback which
reduces the equivalent source impedance. (I am not talking ALC here, ALC
is in the form of dynamic power control rather than reducing the
equivalent source impedance, though you could be fooled by some steady
state tests into thinking it has reduced the equivalent source
impedance.)

Owen

On Apr 2, 9:20 pm, Owen Duffy wrote:
"K7ITM" wrote in news:1175574896.245112.244360
@y80g2000hsf.googlegroups.com:



On Apr 2, 4:52 pm, Cecil Moore wrote:
K7ITM wrote:
...
seen a great many examples of it. I gave a few of them earlier. I've
also worked on the design of broadband RF amplifiers which are
designed specifically to be 50 ohm resistive sources, through the use
of feedback to set that impedance. You don't need brute-force

Tom, I suggest that amplifiers with a specific equivalent source
impedance to low tolerance don't happen by accident or by magic of a PI
coupler, they require design measures that are not usually applied to
amplifiers for SSB telephony.

Absolutely. The amplifier designs I referred to took some work to get
"right."

The assertions here that "conjugate matching" occurs naturally as a by-
product of peaking the PA is not consistent with the realities of design
of amplifiers with specific equivalent source impedance.

If I understand you correctly, I again fully agree. The design goals
of ham, and for that matter most commercial, RF power amplifiers put
things like decent efficiency, low distortion and stable operation
well ahead of any consideration to design to a particular output port
source impedance. Rarely is that ever even considered, since it
doesn't matter.

The amplifier configuration I used as an example was a single ended class
B valve RF linear with PI coupler for SSB telephony for comparison with
Walt's test. A push pull class B bipolar transistor amplifier with
broadband transformer coupling and high pass filter will behave
differently, and some of those designs include negative feedback which
reduces the equivalent source impedance. (I am not talking ALC here, ALC
is in the form of dynamic power control rather than reducing the
equivalent source impedance, though you could be fooled by some steady
state tests into thinking it has reduced the equivalent source
impedance.)

Owen

I would point out that negative feedback does not necessarily reduce
the output impedance. Voltage-derived negative feedback does, but
current-derived negative feedback increases output impedance. If you
analyze the difference between a grounded-cathode and a grounded-grid
amplifier from the point of view of negative feedback, you will see
that the grounded grid amplifier has higher source impedance, viewed
at the plates. The driver source impedance in the cathode circuit
effectively monitors the cathode current (which is very nearly equal
to the plate current), and generates negative feedback to the grid-
cathode voltage as a result. Adding a small cathode resistance to a
grounded-cathode amplifier will have a similar effect; the effect on
the impedance seen at the plates is much greater than the resistance
placed in the cathode circuit. What you see through a pi or other
coupling network depends on that network, as shown in the examples I
posted earlier today, and generally will be much different than what
happens at the plates.

Actually, the comparison of a grounded-cathode and a grounded-grid
amplifier is a good illustration of how the plate source impedance and
the optimal load impedance are unrelated. The change between those
two types, for a given tube and given plate voltage, has a minor
effect on optimal load impedance, and a major effect on plate source
impedance.

Cheers,
Tom

"K7ITM" wrote in
ups.com:

Actually, the comparison of a grounded-cathode and a grounded-grid
amplifier is a good illustration of how the plate source impedance and
the optimal load impedance are unrelated. The change between those
two types, for a given tube and given plate voltage, has a minor
effect on optimal load impedance, and a major effect on plate source
impedance.

Tom,

A good point!

I am playing around with a model of 4 x 811A in GG followed by a PI
coupler into a nominal 50 ohm load to explore the small delta dynamic
source resistance, and the common cathode configuration would be an
interesting contrast. The interesting thing in modelling the GG triode
class B config is that the changing driver load as Ia changes (ie the
feedback) will vary in effect depending on the equivalent source
impedance of the driver. Again another variable that mitigates against
the accidental "conjugate match".

Owen

Keith Dysart wrote:
In light of your new approach, which I wholeheartedly
endorse, perhaps you will reconsider your response in the
other threads and try to "understand the nature of the
source starting with the simplest one".

I have pointed out the error in your calculation of the
reflection coefficient but you have ignored it. I don't
know what more I can do. You seem to be allowing output
and blocking input.
--
73, Cecil http://www.w5dxp.com