On Mon, 16 Jun 2008 03:32:23 GMT, Owen Duffy wrote:

The analysis is waiting for me to build the
analytical equations for the negative feedback due to cathode
degeneration in a grounded grid configuration.

Hi Owen,

Consult the work of H.W. Bode taken from his lectures at Bell Labs ca.
1939, and then rendered into text as:
Network Analysis and Feedback Amplifier Design,
Chapter IV Mathematical Definition of Feedback
4.2 Return Voltage and Reduction in Effect of Tube Variations p 46
It attends specifically (grounded grid triode) what you call out
above.

In a nutshell, Output (or Input) Z can be tailored by what is called
the "noise gain" of an amplifier. In today's parlance, that is that
portion of Open loop gain that is fed back to the input to create what
is called closed loop gain ("noise gain" is simply the difference when
all gains are expressed as dB). The higher the "noise gain" the lower
the output Z (or higher the input Z) compared to the native (open
loop) Z. There are a host of other characteristics improvements that
flow from this same boon offered by "noise gain" (dynamic range, noise
rejection, linearity, CMRR, PSRR, and so on).

This shorthand can be found expanded in discussion in
5.5 Effect of Feedback on Input and Output Impedances of
Amplifiers
bullets 1. through 4. but it serves the reader to really stick with
the first 4 chapters to gain the proficiency to tackle the remaining
15 as the text is heavily cross-referential.

The general formula can be found at:
5.11 Exact Formula for External Gain with Feedback (5-30)

Bode was not simply a chalk-and-talk theorist wholly ignorant of the
practical realities as are evidenced in several chapter headings:
Chapter VII Stability and Physical Realizability

Chapter IX Physical Representation of Driving Point Impedance
Functions

Chapter XI Physical Representation of transfer Impedance Functions

Chapter XIII General Restrictions on Physical Network
Characterizations

Ultimately, it takes very little reading applied to the conventional
designs found in Amateur class amplifiers to discover there is really
very, very little modification of amplifier characteristics offered
through negative feedback design (it costs too much). In fact, I
would say none whatever - hence the heavy filtering at the outputs and
the customers' universal acceptance of barely mediocre performance. It
might be said that every transmitter owned by hams is a museum of
1930s performance. And for those who mistake the feedback of
stabilization (barely found in those same cheap designs) - this is not
negative feedback, it is compensation. It too has scant effect on
tailoring (reducing/increasing) impedances.

As I am undoubtedly the only copy holder of this book in this group,
access can be obtained through:

http://books.google.com/books?client...G=Search+Books
which will provide a surplus of leads, if not the exact title. Some
links might provide a pdf, others full access, yet others limited
access, and most have links to copies in the market place.

Given the usual confusion over what constitutes a Conjugate match
(when most argue an Impedance match in its place) says discussion of
"Efficiency and maximum power transfer" without more rigorous
resources fails to even reach the level of tepid conjecture.

Bottom line is the source presents a real resistance and no appeal to
ratios, linearity, load lines, fly-wheels, or partial cycles is
necessary to arrive at a definitive value (which, to this point has
been notably absent in the face of obviously localized heat and loss).
There is plenty of discussion of what it is NOT, but none seem to know
what it IS. That the typical Amateur amplifier source Z is
demonstrable is embarrassment enough to this shortfall of expertise.
(The pile of theories, books and formulas merely support the obvious,
not replace it.)

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Mon, 16 Jun 2008 03:32:23 GMT, Owen Duffy wrote:

The analysis is waiting for me to build the
analytical equations for the negative feedback due to cathode
degeneration in a grounded grid configuration.

Hi Owen,

Consult the work of H.W. Bode taken from his lectures at Bell Labs ca.
1939, and then rendered into text as:
Network Analysis and Feedback Amplifier Design,
Chapter IV Mathematical Definition of Feedback
4.2 Return Voltage and Reduction in Effect of Tube Variations p 46
It attends specifically (grounded grid triode) what you call out
above.

In a nutshell, Output (or Input) Z can be tailored by what is called
the "noise gain" of an amplifier. In today's parlance, that is that
portion of Open loop gain that is fed back to the input to create what
is called closed loop gain ("noise gain" is simply the difference when
all gains are expressed as dB). The higher the "noise gain" the lower
the output Z (or higher the input Z) compared to the native (open
loop) Z. There are a host of other characteristics improvements that
flow from this same boon offered by "noise gain" (dynamic range, noise
rejection, linearity, CMRR, PSRR, and so on).

This shorthand can be found expanded in discussion in
5.5 Effect of Feedback on Input and Output Impedances of
Amplifiers
bullets 1. through 4. but it serves the reader to really stick with
the first 4 chapters to gain the proficiency to tackle the remaining
15 as the text is heavily cross-referential.

The general formula can be found at:
5.11 Exact Formula for External Gain with Feedback (5-30)

Bode was not simply a chalk-and-talk theorist wholly ignorant of the
practical realities as are evidenced in several chapter headings:
Chapter VII Stability and Physical Realizability

Chapter IX Physical Representation of Driving Point Impedance
Functions

Chapter XI Physical Representation of transfer Impedance Functions

Chapter XIII General Restrictions on Physical Network
Characterizations

Ultimately, it takes very little reading applied to the conventional
designs found in Amateur class amplifiers to discover there is really
very, very little modification of amplifier characteristics offered
through negative feedback design (it costs too much). In fact, I
would say none whatever - hence the heavy filtering at the outputs and
the customers' universal acceptance of barely mediocre performance. It
might be said that every transmitter owned by hams is a museum of
1930s performance. And for those who mistake the feedback of
stabilization (barely found in those same cheap designs) - this is not
negative feedback, it is compensation. It too has scant effect on
tailoring (reducing/increasing) impedances.

As I am undoubtedly the only copy holder of this book in this group,
access can be obtained through:

http://books.google.com/books?client...G=Search+Books
which will provide a surplus of leads, if not the exact title. Some
links might provide a pdf, others full access, yet others limited
access, and most have links to copies in the market place.

Given the usual confusion over what constitutes a Conjugate match
(when most argue an Impedance match in its place) says discussion of
"Efficiency and maximum power transfer" without more rigorous
resources fails to even reach the level of tepid conjecture.

Bottom line is the source presents a real resistance and no appeal to
ratios, linearity, load lines, fly-wheels, or partial cycles is
necessary to arrive at a definitive value (which, to this point has
been notably absent in the face of obviously localized heat and loss).
There is plenty of discussion of what it is NOT, but none seem to know
what it IS. That the typical Amateur amplifier source Z is
demonstrable is embarrassment enough to this shortfall of expertise.
(The pile of theories, books and formulas merely support the obvious,
not replace it.)

73's
Richard Clark, KB7QHC

Hi Richard,
A more modern treatment is _High Linearity RF Amplifier
Design_ by Peter B. Kenington. ISBN 1-58053-143-1. I think Amazon
still carries it.
73,
Tom Donaly, KA6RUH

Owen Duffy wrote:
(Richard Harrison) wrote in news:23000-
:

Jim Lux wrote:
"in a linear system"

It produces no significant harmonics, so the system is linear.

That is a new / unconventional definition of 'linear'.

The term is usually used in this context to mean a linear transfer
characteristic, ie PowerOut vs PowerIn is linear.

Or, as I used it, that superposition holds.
One can build an amplifier or other device where the Pout(Pin) =straight
line, but is not linear in the formal sense. Say you built a widget that
measured the input frequency and amplitude, then drove a synthesizer at
that frequency and amplitude = 2*input amplitude.


Considering a typical valve Class C RF amplifier with a resonant load:

Conduction angle will typically be around 120°, and to achieve that, the
grid bias would be around twice the cutoff voltage.

If you attempted to pass a signal such as SSB though a Class C amplifier
that was biased to twice the cutoff value, there would be no output
signal when the peak input was less than about 50% max drive voltage, or
about 25% power, and for greater drive voltage there would be output. How
could such a transfer characteristic be argued to be linear?

It would not be.You're right

The active device isn't linear.
neither is the whole assembly.

I think, though, that sometimes we take a more casual view of linear
(e.g. people talk about the linearity of a log detector.. referring to
the deviation from a Voltage out=dBm in straight line.)

And, some confusion about nonlinear devices in a building block that is,
by and large, linear (e.g. a power op amp with an AB2 output stage and a
fair amount of negative feedback) with some constraints on frequency and
amplitude.

Owen

Richard Clark wrote:

Ultimately, it takes very little reading applied to the conventional
designs found in Amateur class amplifiers to discover there is really
very, very little modification of amplifier characteristics offered
through negative feedback design (it costs too much). In fact, I
would say none whatever - hence the heavy filtering at the outputs and
the customers' universal acceptance of barely mediocre performance. It
might be said that every transmitter owned by hams is a museum of
1930s performance. And for those who mistake the feedback of
stabilization (barely found in those same cheap designs) - this is not
negative feedback, it is compensation. It too has scant effect on
tailoring (reducing/increasing) impedances.


probably not "every transmitter", but certainly the vast majority of
designs, particularly those for HF based on tubes in the ARRL handbook
(and by extension, those sold to readers of the handbook).

Cost *is* a factor. The Harris PWM modular transmitters are very cool,
but beyond the means of most hams as a commercially manufactured item
(in that, the NRE for a consumer mfr to get there would be prohibitively
high)


One should also not neglect that the hobby aspect of ham radio provides
an incentive (for some) to preserve fine (or not so fine) examples of
past radio art. No more unusual than steam train fans or classic auto
collectors. There is a visceral satisfaction of seeing those glowing
tubes with the plates changing color, notwithstanding that the RF
performance, in objective terms, is horrid.





As I am undoubtedly the only copy holder of this book in this group,
access can be obtained through:

I'll bet not..grin

Owen Duffy wrote:
"... but asserting that things are linear because there are no harmonics
is wrong and being so, is no support for your atgument."

No one is arguing that an amplitude modulated wave can be amplified by a
Class C amplifier stage unimpaired by amplitude distortion.

Terman wrote on page 525 0f his 1955 opus:
"Amplitude distortion exists when the modulation envelope contains
frequency components not present in the modulating signal. Thus if the
modulating signal is a sine wave, then amplitude distortion will cause
the envelope to contain harmonics of the modulating signal, which in
turn denotes the presence of high-order sideband components that differ
from the carrier frequency by harmonics of the modulating frequency."

I`ve used microwave system performance monitors which alarmed on this
principle.

If there are no harmonics there is no distortion no matter how lousy the
transfer function. It is legal to filter out noise and distortion.

Best regards, Richard Harrison, KB5WZI

Richard Clark wrote:
On Mon, 16 Jun 2008 03:32:23 GMT, Owen Duffy wrote:

The analysis is waiting for me to build the
analytical equations for the negative feedback due to cathode
degeneration in a grounded grid configuration.

Hi Owen,

Consult the work of H.W. Bode taken from his lectures at Bell Labs ca.
1939, and then rendered into text as:


Hi Richard,

In this group, would not the work of Vaughn Bode be more appropriate?


- 73 de Mike N3LI -

"Jim Lux" wrote in message
...
Owen Duffy wrote:
(Richard Harrison) wrote in news:23000-
:

Jim Lux wrote:
"in a linear system"

It produces no significant harmonics, so the system is linear.

That is a new / unconventional definition of 'linear'.

The term is usually used in this context to mean a linear transfer
characteristic, ie PowerOut vs PowerIn is linear.

Or, as I used it, that superposition holds.
One can build an amplifier or other device where the Pout(Pin) =straight
line, but is not linear in the formal sense. Say you built a widget that
measured the input frequency and amplitude, then drove a synthesizer at
that frequency and amplitude = 2*input amplitude.


Considering a typical valve Class C RF amplifier with a resonant load:

Conduction angle will typically be around 120°, and to achieve that, the
grid bias would be around twice the cutoff voltage.

If you attempted to pass a signal such as SSB though a Class C amplifier
that was biased to twice the cutoff value, there would be no output
signal when the peak input was less than about 50% max drive voltage, or
about 25% power, and for greater drive voltage there would be output. How
could such a transfer characteristic be argued to be linear?

It would not be.You're right

The active device isn't linear.
neither is the whole assembly.

I think, though, that sometimes we take a more casual view of linear
(e.g. people talk about the linearity of a log detector.. referring to
the deviation from a Voltage out=dBm in straight line.)

And, some confusion about nonlinear devices in a building block that is,
by and large, linear (e.g. a power op amp with an AB2 output stage and a
fair amount of negative feedback) with some constraints on frequency and
amplitude.

Owen

Owen, I didn't realize that this thread was specific to 'linear transfer
characteristic'. I thought the thread topic was sufficiently broad so as to
include the subject of linearity of the output of the tank circuit that permits
the use of theorems that require the output to be linear. Richard H's and my
posts were simply reminders that the energy storage in the tank circuit is the
reason for the linear relation between voltage and current at the output of both
Class B and C amplifiers that results in a sine wave. From that perspective I
believed our posts were legitimate to the thread topic. Apparently we were
wrong.

And Owen, I'm somewhat surprised that you don't agree with the flywheel analogy
with respect to the smoothing effect of the energy storage in the tank circuit.
This analogy has been around for decades--it's not my invention. IMHO, the
periodic energy spurts from the pistons entering the flywheel is precisely an
analog of the energy spurts of the periodic current pulses entering the tank
citcuit. Why do you not agree? Even the pendulum swing is appropriate, because
if you trace the position of the pendulum with respect to time you'll discover
the trace is a perfect sine wave, while the short spurt of energy supplied by
the spring at the beginning of each cycle is just sufficient to overcome the
energy dissipated due to friction at the axis plus the aerodynamic resistance.
How could this not be an appropriate analogy? Sorry to have forced you away from
the thread topic with questions not pertaining to the thread.

I am also curious as to why the subject of 'linear transfer characteristic' with
respect to Class C amps was even considered, because the Class C amp has always
been known to have a distorted output relative to its input. I would agree that
the subject is appropriate when considering Class AB and B amplifiers, but not
C.

Walt, W2DU

On Mon, 16 Jun 2008 00:08:14 -0700, "Tom Donaly"
wrote:

Hi Richard,
A more modern treatment is _High Linearity RF Amplifier
Design_ by Peter B. Kenington. ISBN 1-58053-143-1. I think Amazon
still carries it.
73,
Tom Donaly, KA6RUH

Thanx Tom.

73's
Richard Clark, KB7QHC

Jim Lux wrote in
:

....
That is a new / unconventional definition of 'linear'.

The term is usually used in this context to mean a linear transfer
characteristic, ie PowerOut vs PowerIn is linear.

Or, as I used it, that superposition holds.
One can build an amplifier or other device where the Pout(Pin)
=straight line, but is not linear in the formal sense. Say you built a
widget that measured the input frequency and amplitude, then drove a
synthesizer at that frequency and amplitude = 2*input amplitude.


Yes Jim, I should have written Vout/Vin is linear, that Vout(Vin) has no
significant terms higher than first order.

Noting that a single ended Class B or AB amplifier can only be linear
when a resonant load or suitable filter is included as part of the
system.

Elsewhere it was suggested that I do not accept the 'flywheel'
explanation of the tank circuit. That is not true, but it is a limited
explanation, simple, and appealing, but limited.

Another explanation is to view the anode current waveform as containing a
DC component, a fundamental component and harmonic components and a
filter that adequately reduces the undesired components provides the
solution to a single ended Class B or AB linear amplifier. The filter is
not restricted to a resonant 'tank' circuit.

I have modelled the operating characteristics of my HF linear using 4
572B in AB2. An FFT of the anode current reveals the spectral content, it
is plotted at http://www.vk1od.net/lost/572BIaSpectrum.png . Of course,
the output filter must only select the fundamental component for linear
operation, selection of a harmonic would not be acceptable for a complex
input waveform because it would destroy the absolute relationship between
different frequency components of the input.

Owen

"Walter Maxwell" wrote in
:


"Jim Lux" wrote in message
...
Owen Duffy wrote:
(Richard Harrison) wrote in news:23000-
:

Jim Lux wrote:
"in a linear system"

It produces no significant harmonics, so the system is linear.

That is a new / unconventional definition of 'linear'.

The term is usually used in this context to mean a linear transfer
characteristic, ie PowerOut vs PowerIn is linear.

Or, as I used it, that superposition holds.
One can build an amplifier or other device where the Pout(Pin)
=straight line, but is not linear in the formal sense. Say you built
a widget that measured the input frequency and amplitude, then drove
a synthesizer at that frequency and amplitude = 2*input amplitude.


Considering a typical valve Class C RF amplifier with a resonant
load:

Conduction angle will typically be around 120°, and to achieve
that, the grid bias would be around twice the cutoff voltage.

If you attempted to pass a signal such as SSB though a Class C
amplifier that was biased to twice the cutoff value, there would be
no output signal when the peak input was less than about 50% max
drive voltage, or about 25% power, and for greater drive voltage
there would be output. How could such a transfer characteristic be
argued to be linear?

It would not be.You're right

The active device isn't linear.
neither is the whole assembly.

I think, though, that sometimes we take a more casual view of linear
(e.g. people talk about the linearity of a log detector.. referring
to the deviation from a Voltage out=dBm in straight line.)

And, some confusion about nonlinear devices in a building block that
is, by and large, linear (e.g. a power op amp with an AB2 output
stage and a fair amount of negative feedback) with some constraints
on frequency and amplitude.

Owen

Owen, I didn't realize that this thread was specific to 'linear
transfer characteristic'. I thought the thread topic was sufficiently

Richard stated "It produces no significant harmonics, so the system is
linear." It is that with which I disagree.

....
And Owen, I'm somewhat surprised that you don't agree with the
flywheel analogy with respect to the smoothing effect of the energy
storage in the tank circuit. ...

I have not disagreed with that in anything that I wrote.

...
I am also curious as to why the subject of 'linear transfer
characteristic' with respect to Class C amps was even considered,
because the Class C amp has always been known to have a distorted
output relative to its input. I would agree that the subject is
appropriate when considering Class AB and B amplifiers, but not C.


Because Richards statement quoted above (which must be about transfer
linearity) is being used to support your assertion that the PA is linear
in its terminal V/I response with changing load.

Walt, the thread has become muddled with helpers muddying the water. Your
proposition needs to be argued with a single logically developed sound
argument. Your Chapter 19 tries to do that.

I have already stated that (as yet?) I am unconvinced, and I make the
observation that I am not alone. I will work through resolving the
apparent inconsistencies in my own time and without the confusion of
whether or not harmonics exist or more correctly the extent to which they
exist, and what that might mean.

Owen