Owen Duffy wrote in news:Xns9D81BC11E3183nonenowhere@
61.9.191.5:

"Sven Lundbech" wrote in
k:

...
As mentioned earlier, most of the stuff is old hat to me - but I
really look forward to dig into the chapters concerning tx output
impedance. A highly controversial subject for decades.

Here is a simple little test for the hypothesis that Zs=50+j0 that uses
equipment found in many if not most HF ham shacks.

Oh, the URL: http://vk1od.net/blog/?p=1028 .


Owen

On May 23, 4:31*am, Owen Duffy wrote:
Owen Duffy wrote in news:Xns9D81BC11E3183nonenowhere@
61.9.191.5:

"Sven Lundbech" wrote in
. dk:

...
As mentioned earlier, most of the stuff is old hat to me - but I
really look forward to dig into the chapters concerning tx output
impedance. A highly controversial subject for decades.

Here is a simple little test for the hypothesis that Zs=50+j0 that uses
equipment found in many if not most HF ham shacks.

Oh, the URL:http://vk1od.net/blog/?p=1028.
Owen

While the analysis of transmitter output impedance in Reflections is
flawed,
experiments (claimed to be repeatable) described in Reflections appear
to
support the conclusions of the flawed analysis.

It would be highly valuable if the results of these experiments could
be
explained in a manner that aligns with established understandings.

Such an explanation might start by describing the circuit conditions
that
result from following the manufacturer’s tuning procedures. After
all,
these usually depend on measuring currents and voltages so are only
indirectly related to power. Perhaps the resulting conditions are not
as they are usually assumed to be.

Try as I might, I have not been able to derive a mechanism to explain
the observations in Reflections. But the explanations offered in
Reflections require large chunks of linear circuit theory to be
discarded,
so this does not seem to be an appropriate path.

....Keith

On May 24, 6:30*am, Keith Dysart wrote:
Such an explanation might start by describing the circuit conditions
that result from following the manufacturer’s tuning procedures.

On an old tube transmitter, e.g. a Globe Scout, when the manufacturer
specifed a particular grid current and a particular plate current,
does that imply a particular single resistive load line for the final
tube? Why were those particular grid and load currents chosen? Maximum
efficiency? Tube life? Minimum distortion?
--
TNX & 73, Cecil, w5dxp.com

On May 24, 9:23*am, Cecil Moore wrote:
On May 24, 6:30*am, Keith Dysart wrote:

Such an explanation might start by describing the circuit conditions
that result from following the manufacturer’s tuning procedures.

On an old tube transmitter, e.g. a Globe Scout, when the manufacturer
specifed a particular grid current and a particular plate current,
does that imply a particular single resistive load line for the final
tube? Why were those particular grid and load currents chosen? Maximum
efficiency? Tube life? Minimum distortion?

Excellent questions. I have often wondered if the manufacturer's
tuning
procedures had anything to do with maximizing output power transfer,
or
were they, in fact, optimizing some other aspect.

....Keith

On Mon, 24 May 2010 07:06:44 -0700 (PDT), Keith Dysart
wrote:

I have often wondered if the manufacturer's
tuning
procedures had anything to do with maximizing output power transfer,
or
were they, in fact, optimizing some other aspect.

This resolves quickly in measurement - no need to wonder unless it
offers some secondary benefit of not measuring things.

An alternative is to simply examine conventional design
considerations. One can add to Plate current by throwing a lot of
power into the grid. More plate current yields more output power
results, but grid lifetime plumments.

One can do innumerable things to force an artificial outcome that
strains to prove a distorted logic. Examining a suite of sources, in
initial conditions that are average for their application quickly
reveals a common design paradigm.

******

The fundamental answer to your question is the manufacturer ultimately
designs for market domination, or maximum investment return (the two
don't necessarily converge). Thus the marketplace gives us a spectrum
of choice and the norm of the distribution reveals cautious design
that has its eye on a value exchange expressed in money. THAT is the
only optimization you can expect = in an honest barter, you get what
you pay for.

73's
Richard Clark, KB7QHC

On May 24, 6:58*pm, Richard Clark wrote:
On Mon, 24 May 2010 07:06:44 -0700 (PDT), Keith Dysart

wrote:
I have often wondered if the manufacturer's
tuning
procedures had anything to do with maximizing output power transfer,
or
were they, in fact, optimizing some other aspect.

This resolves quickly in measurement - no need to wonder unless it
offers some secondary benefit of not measuring things. *

An alternative is to simply examine conventional design
considerations. *One can add to Plate current by throwing a lot of
power into the grid. *More plate current yields more output power
results, but grid lifetime plumments.

One can do innumerable things to force an artificial outcome that
strains to prove a distorted logic. *Examining a suite of sources, in
initial conditions that are average for their application quickly
reveals a common design paradigm.

******

The fundamental answer to your question is the manufacturer ultimately
designs for market domination, or maximum investment return (the two
don't necessarily converge). *Thus the marketplace gives us a spectrum
of choice and the norm of the distribution reveals cautious design
that has its eye on a value exchange expressed in money. *THAT is the
only optimization you can expect = in an honest barter, you get what
you pay for.

73's
Richard Clark, KB7QHC

You have gone to a bit higher level than I intended with my question
and
I agree with you conclusions at that level. But my question was more
basic.

When designing the filter for a PA, among other things, one uses the
desired load to be applied to the tube and the disired load impedance
to be supported and selects filter components to perform the desired
transformation.

When operating the radio, the operator has meters that measure some
values, some knobs that control some component values and a procedure
for adjusting these knobs.

It is not at all obvious what exactly the result of performing the
procedure is. Does it result in the same load being applied to the
tube that was computed by the designer? There are some hints that
the procedure will result in the load applied to the tube being
real, but beyond that, what exactly are the circuit conditions
that result?

....Keith

On Mon, 24 May 2010 16:23:26 -0700 (PDT), Keith Dysart
wrote:

It is not at all obvious what exactly the result of performing the
procedure is. Does it result in the same load being applied to the
tube that was computed by the designer?

Hi Keith,

By and large, Yes.

There are some hints that
the procedure will result in the load applied to the tube being
real, but beyond that, what exactly are the circuit conditions
that result?

I am a little lost on that. The load applied is the load applied
(sorry for the Zen). If you mean that the load is transformed by
tuning to a real R for the Plate to see, then, yes, that is operative.

However, that is not the end of it. That R is seen as the loss of a
now-poorer Q for the Plate tank. This is the distinction between
loaded and unloaded Q. The Plate tank Q expressed in terms of loaded
Q, to be effective, is quite low in comparison to its unloaded value.
This value of loaded Q is roughly between 10 and 20 where the
components in isolation (unloaded) could easily achieve 10 to 30 times
that.

The term "loaded" includes BOTH the plate and the applied load
(whatever is presented to the antenna connection). The only time the
unloaded Q of the Plate tank is at peak value is when it is sitting in
isolation from the chassis, circuitry, and even mounts - which means
it is not very useful in that configuration, except as a trophy. Many
silver plate their tanks as trophies (because this rarely results in
better operation).

Now, let's return to my statement about what Q is "effective" AND that
it measures out at roughly 10 to 20. This is straight out of Terman
if you need a citation. As for explanation (also found in Terman),
you have to consider that the Plate tank is the gate-keeper (as well
as transformer of Z) of power. If you have too high a Q, the power is
not getting THROUGH the tank as it must, and necessarily it remains in
the tank (as energy, albeit).

Consider further that ALL resonant circuits can be cast from series
circuits to parallel circuits or parallel to series (a fact lost on
some inventors of antennas). To describe the Plate tank in series
terms as I do, then the plate resistance and load resistance combine
in series through a simple circular path through ground. There are
parallel tank designs where the resistances combine in parallel. The
net result is the same insofar as Q is concerned.

Consult Terman if that is confusing. No doubt others will either more
clearly cite him, or add to the confusion.

73's
Richard Clark, KB7QHC

Hello Keith,

Thank you for your response. I’m starting my answer to your statements
by first quoting from one of your posts:

“Try as I might, I have not been able to derive a mechanism to explain
the observations in Reflections. But the explanations offered in
Reflections require large chunks of linear circuit theory to be
discarded, so this does not seem to be an appropriate path.”

That you have been unable to derive a mechanism that explains the
action in an RF power amplifier is evidence that you do not understand
it. So let’s examine the action that follows an appropriate path that
does not require any linear circuitry to be discarded. Further
evidence that you do not understand it is that you used a bench power
supply to describe the action, which you state has an infinite source
resistance when the load exceeds 50 ohm, and zero source resistance
when the load is less than 50 ohms. Unfortunately, this power supply
in no way resembles an RF power amplifier, either in components or
action.

We’ll begin by stipulating that the ‘filter’ is a pi-network tank
circuit, having a tuning capacitor at the input and a loading-
adjustment capacitor at the output. We’ll also stipulate that the
plate voltage and the grid bias are set to provide the desired
conditions at the input of the tank circuit, which means that the
desired grid voltage is that which results in the desired conduction
time for the applied plate voltage. The result provides a dynamic
resistance RL, which is determined by the average plate voltage VPavg
and the average plate current IPavg appearing at the terminals leading
to the input of the tank circuit. In other words, RL = VPavg/IPavg.
To permit delivery of all available power to be delivered by the
dynamic resistance RL, we want the input impedance appearing at the
input of the tank circuit to be equal to RL.

We’ll now go to the output of the tank circuit. We’ll assume the load
to be the input of a transmission line on which there are reflections.
The result is that the input to the line contains a real component R
and a reactance jX. The output terminals of the tank circuit are the
two terminals of the output-loading capacitor. When the line is
connected to the output terminals of the tank circuit the reactance
appearing at the line input is reflected into the tank circuit. This
reactance is then cancelled by the tuning capacitor at the input of
the tank circuit, resulting in a resonant tank circuit. We now need to
adjust the output-loading capacitor to apply the correct voltage
across the input of the transmission line so that the real component R
appearing at the line input is reflected into the tank circuit such
that the resistance RL appears at the input of the tank circuit, thus
allowing all the available power to enter the tank circuit. In other
words, adjusting the loading capacitor to deliver all the available
power into the line also makes the output resistance of the tank
circuit equal to the real component R appearing at the line input.
With any other value of output resistance of the source, all the
available power would not be delivered to the line. A corollary to
that condition follows from the Maximum Power Transfer Theorem that
for a given output resistance of the source (the tank circuit), if the
load resistance is either increased for decreased from the value of
the source resistance, the delivery of power will decrease. This
condition also accurately describes the condition for the conjugate
match.
Keep in mind that the input impedance of the line is complex, or
reactive, but the reactance of the correctly-adjusted tuning capacitor
has introduced the correct amount of the opposite reactance to cancel
the reactance appearing at the line input. Thus the line input
impedance is R + jX and the output impedance of the source is R – jX,
providing the conjugate match.

You stated in one of your posts that the phase of the reflected wave
in relation to that of the source wave results in a non-linear
condition. This is totally untrue. The tuning action of the input
capacitor in the tank circuit that cancels the line reactance caused
by the reflection on the line in no way introduces any non-linearity
in the circuit, and the condition in the vicinity of the output of the
tank circuit is totally linear. Thus, circuit theorems that require
linearity to be valid are completely valid when used with the RF power
amplifier as described above. This applies to all RF power amplifiers,
Class A, AB, B and C.

I hope my comments above assist in understanding the action that
occurs in RF power amplifiers.

Walt Maxwell, W@DU

On May 24, 7:30*am, Keith Dysart wrote:
On May 23, 4:31*am, Owen Duffy wrote:



Owen Duffy wrote in news:Xns9D81BC11E3183nonenowhere@
61.9.191.5:

"Sven Lundbech" wrote in
. dk:

...
As mentioned earlier, most of the stuff is old hat to me - but I
really look forward to dig into the chapters concerning tx output
impedance. A highly controversial subject for decades.

Here is a simple little test for the hypothesis that Zs=50+j0 that uses
equipment found in many if not most HF ham shacks.

Oh, the URL:http://vk1od.net/blog/?p=1028.
Owen

While the analysis of transmitter output impedance in Reflections is
flawed,
experiments (claimed to be repeatable) described in Reflections appear
to
support the conclusions of the flawed analysis.

It would be highly valuable if the results of these experiments could
be
explained in a manner that aligns with established understandings.

Such an explanation might start by describing the circuit conditions
that
result from following the manufacturer’s tuning procedures. After
all,
these usually depend on measuring currents and voltages so are only
indirectly related to power. Perhaps the resulting conditions are not
as they are usually assumed to be.

Try as I might, I have not been able to derive a mechanism to explain
the observations in Reflections. But the explanations offered in
Reflections require large chunks of linear circuit theory to be
discarded,
so this does not seem to be an appropriate path.

...Keith

Keith, would you please elaborate on why you believe my analysis of
transmitter output impedance is flawed? And what is the basis for your
belief that my explanations in Reflections require large chunks of
linear circuit theory to be discarded. Could it be because you
consider the source resistance in the transmitter to be dissipative,
as in the classical generator? If so, you must be made to realize that
the source resistance of the transmitter is non-dissipative, which is
the reason that its efficiency can exceed 50%.

Or are you considering the output characteristic of the transmitter to
be non-linear? This is not the case, because the effect of energy
storage in the tank circuit isolates the non-linear input from the
output circuit, which is linear as evidenced by the almost perfect
sine wave appearing at the output of the tank.

One last question: Are you basing your dissatisfaction of Reflections
from reviewing the 2nd or 3rd edition? Chapter 19 has been expanded in
the 3rd edition, in which I presented additional proof of my position
on the subject that you should be aware of. If you haven't yet seen
the addition that appears in the 3rd ed, please let me know so that I
can send you a copy of the addition. Also include your email address
so I can send it.

Keith, you are the only person I know of who appears to have found
flaws in my presentation on this subject. Which is why I'm anxious to
know exactly why you believe my presentation is flawed.

Walt Maxwell, W2DU

On May 24, 10:55*am, walt wrote:
Keith, would you please elaborate on why you believe my analysis of
transmitter output impedance is flawed? And what is the basis for your
belief that my explanations in Reflections require large chunks of
linear circuit theory to be discarded. Could it be because you
consider the source resistance in the transmitter to be dissipative,
as in the classical generator? If so, you must be made to realize that
the source resistance of the transmitter is non-dissipative, which is
the reason that its efficiency can exceed 50%.

No problems there. There has been much confusion in this area and
anything
that reduces this confusion is beneficial.

Or are you considering the output characteristic of the transmitter to
be non-linear? This is not the case, because the effect of energy
storage in the tank circuit isolates the non-linear input from the
output circuit, which is linear as evidenced by the almost perfect
sine wave appearing at the output of the tank.

This may be the root of my disagreement. Certainly the output can be
an
arbitrarily perfect sine wave, but this simply depends on the
characteristics of the filter and not on whether the system is linear.

But the way the filter transforms the impedances is the crux of the
issue.

It is my understanding that the input impedance to a filter can be
computed by starting with the load impedance applied to the filter and
then, using the rules for series and parallel connected components,
compute the way through the filter until reaching the input and the
result is the input impedance to the filter.

Similarly, the output impedance of the filter can be computed by
starting with source impedance driving the filter, series and
paralleling
the components until reaching the output and the result is the output
impedance of the filter.

The desired impedance for the input to the filter is that impedance
which
produces the desired load on the tube. And the component values are
computed to produce this load on the tube when the correct load is
attached to the output.

For the output impedance of the filter, the question then becomes:
What
is the source impedance driving the filter? If the source is
constructed
as a Class A amplifier, then it depends on the controlling device,
and
for the simplest of circuits would be Rp of the tube. (Just for
clarity,
in this discussion Rp is the slope of the plate E/I curve with
constant
grid voltage. In an ideal tube, these lines are equidistant apart and
the
slopes are the same. Real tubes, of course, are not so well behaved,
but
this should not affect the basic discussion.)

Since the component values for the filter were chosen to provide the
optimum load to the tube, and the optimum load value has no relation
to
Rp, there is no reason to expect the filter will transform Rp to be
the conjugate of the load impedance.

For amplifiers where conduction is not for 360 degrees (Class AB, B,
C),
the controlling device is no longer time-invariant so the rules for
linear circuit analysis no longer apply. None-the-less, for example,
consider a Class AB amplifier where the tube is only cut off for 1
degree. This short cut-off would not have much affect so the analysis
for Class A would apply. As the cut-off period increases the behaviour
will diverge more and more from that of the Class A amplifier.

Simulations produce some interesting results:

Another way of measuring the source impedance is to observe the effect
on a reflected wave entering the amplifier from the load. With a
Class
C amplifier, simulation reveals that the effect on the reflected wave
depends on the phase of that wave with respect to the drive signal
applied to the tube. As the phase of the reflected wave is changed,
the reflection co-efficient experienced by the wave changes. Truly a
non-linear behaviour. Intriguingly, when the conduction angle is
exactly
180 degrees, this effect largely disappears, and the result is much as
if the source impedance of the tube was 2 times Rp, which seems to
make some sense since the tube is only conducting one-half of the
time.

One last question: Are you basing your dissatisfaction of Reflections
from reviewing the 2nd or 3rd edition? Chapter 19 has been expanded in
the 3rd edition, in which I presented additional proof of my position
on the subject that you should be aware of. If you haven't yet seen
the addition that appears in the 3rd ed, please let me know so that I
can send you a copy of the addition.

I have been reading the .pdfs at w2du.com along with correspondence
and
other writings in QST, QEX and newsgroups.

The expanded Chapter 19 at w2du.com offers more experimental evidence
that seems to support the hypothesis that the transmitter is conjugate
matched to the load after tuning,

But given, from circuit analysis, that the output impedance can not be
well defined for any but a Class A amplifier, the fascinating question
is why is there experimental evidence that agrees with the premise
that
the output impedance of a tuned transmitter is the conjugate match of
the load?

One simple example to consider which has similar behaviour is a bench
power supply that also has a constant current limiter. Set such a
power
supply to produce a voltage of 100V (more precisely a maximum voltage)
and a current limit of 2A. Apply a variable load. Maximum power will
be drawn when the load resistance is 50 ohms. Varying the resistance
on either side of 50 ohms will reduce the power which might be
misconstrued to suggest that the power supply has an output impedance
of 50 ohms, when, in fact, it has a infinite output impedance when
the load is below 50 ohms and a zero output impedance when the load
is above.

I have looked for such a simple explanation in the circuits of the
transmitters used in the experiments but was not able to find one.
So I am still puzzled by the observations.

Also include your email address so I can send it.
Keith.dot.dysart.at.gmail.com .dot. = . .at. = @

…Keith