On Wed, 26 May 2010 04:50:30 -0700 (PDT), Keith Dysart
wrote:

a conjugate match does result in a situation where altering
the load will reduce the power transfer

....

We are still left with the puzzle of why the observations documented
in Reflections report a reduction in power transfer when the load is
changed in either direction.

Hi Keith,

Stripping away everything that you offer as objections to what is not
in Walt's premise (I cannot vouch for his attempts to explain the
universality of it), your statements come into conflict.

If you offer you find a puzzle about measurements, then that is simply
researched at the bench instead of in expansive wanderings in myriad
qualifications. Do you have documented measurements under initial
conditions identical to Walt's that run counter to Walt's quantitative
results?

I suspect not, or we would be talking about competing bench results
instead. This would be a more productive and genuine debate seeking
explanation for what you describe as the "puzzle."

Barring quantitative evidence, anything that continues this rag-chew
is a simple example of "modeling is doomed to succeed."

73's
Richard Clark, KB7QHC

On May 26, 9:17*am, Cecil Moore wrote:
If reflected energy is not allowed to reach the source, why
does the source impedance matter at all?

Continuing this thought thread - Assuming 50 ohm coax from the source
containing a forward traveling wave and no reflected wave, i.e. an SWR
of 1:1 on 50 ohm coax, what it to prohibit us from drawing our system
box through that piece of coax and considering the signal emerging
from that piece of coax to be the linear source signal which is
obviously associated with a V/I = 50 ohm impedance?
--
73, Cecil, w5dxp.com

On May 26, 11:50*am, Richard Clark wrote:
On Wed, 26 May 2010 04:50:30 -0700 (PDT), Keith Dysart

wrote:
a conjugate match does result in a situation where altering
the load will reduce the power transfer

...

We are still left with the puzzle of why the observations documented
in Reflections report a reduction in power transfer when the load is
changed in either direction.

Hi Keith,

Stripping away everything that you offer as objections to what is not
in Walt's premise (I cannot vouch for his attempts to explain the
universality of it), your statements come into conflict.

If you offer you find a puzzle about measurements, then that is simply
researched at the bench instead of in expansive wanderings in myriad
qualifications. *Do you have documented measurements under initial
conditions identical to Walt's that run counter to Walt's quantitative
results?

I suspect not, or we would be talking about competing bench results
instead. *This would be a more productive and genuine debate seeking
explanation for what you describe as the "puzzle." *

Barring quantitative evidence, anything that continues this rag-chew
is a simple example of "modeling is doomed to succeed."

73's
Richard Clark, KB7QHC

Hi Keith,

Sorry, OM, but you still misunderstand various aspects of RF power amp
operation.

First, the power supply is not the limiting factor concerning plate
current. The grid drive is what determines the plate current, and thus
the output power.

Second, the tank circuit is an energy storage device that isolates the
non-linear input from the linear output. That the output is linear is
because the voltage and current are in phase at the output of the tank
circuit. The effect of the energy storage of the tank results in the
tank becoming the source of the energy appearing at the output.

Third, the action of plate resistance Rp occurs only in the formation
of RL, and has no further effect on any action downstream of the input
of the tank circuit. Thus, it has no bearing on the development of the
conjugate match that occurs at the junction of the tank output and the
input of the transmission line.

Fourth, as I said earlier, the the action of the bench power supply
that you presented in no way models the action of the RF power
amplifier. Furthermore, you are incorrect when you say that when
varying the load in either direction causing the power deliver to
decrease there is no conjugate match. In saying what you did violates
the theorem of Maximum Transfer of Power.

Fifth, as I stated earlier, when the reactance appearing at the input
of the load (the transmission line with reflections) is canceled by
the opposite reactance introduced by the pi-network tuning capacitor,
the output impedance of the source (the tank circuit) is the conjugate
of the line-input impedance. If you cannot accept this as fact you
have a problem.

Sixth, your understanding of the effect of the reflected wave on the
source wave is flawed. The non-linearity of the plate current when the
conduction time is less than 360° has no relation to the action
downstream of the input to the tank circuit, because from that point
on the voltage current relationship is linear. If you cannot accept
this as fact you have still another problem.

Seventh, your belief that because there is a conjugate match at the
output of the tank there must be a conjugate match at the input of the
tank is also not true. The effect of the energy storage in the tank
isolates the non-linearity af the input from the linear operation at
the output, permitting a conjugate match at the output, while not
allowing it to occur at the input.

These seven comments are born out (proven) by the results of many
measurements I made using laboratory grade instruments, HP and General
Radio. If you check my record as a professional electrical engineer
regarding the measurements I've made that led to successful hardware
flying on various Earth-orbiting platforms, you must accept the
validity of the measurements I made on RF power amplifiers that prove
my position.

As I said earlier, no one but you has considered my position on this
subject incorrect. Therefore, if you cannot agree with the comments I
made above, but still consider my statements in Reflections flawed,
then there is no point in my making any further comments. I hope
someday you'll finally understand what's really happening within the
RF amplifier.

Walt Maxwell, W2DU

Keith Dysart wrote:
"For the most part, "maximum power transfer is just an interesting
ideosyncracy of linear circuit theory."

In the world of 50 and 60 Hz, we don`t want all the power plant can
supply when we flip on a light switch.

The RF world is usually different.

Maximum power transfer only occurs when source and load match
conjugately, and the match proves the load and source impedances are
equals. It is well known and easily shown that a match results in
maximum power transfer.

If one has a 100-watt transmitter he probably wants 100 watts out of it
sometimes and may only be able to do so when his antenna is matched to
his transmitter,

Maxumum power treansfer is more than an "interesting ideosyncracy".

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Keith Dysart wrote:
"For the most part, "maximum power transfer is just an interesting
ideosyncracy of linear circuit theory."

In the world of 50 and 60 Hz, we don`t want all the power plant can
supply when we flip on a light switch.

The RF world is usually different.

Maximum power transfer only occurs when source and load match
conjugately, and the match proves the load and source impedances are
equals. It is well known and easily shown that a match results in
maximum power transfer.
. . .

It's also easily shown that it doesn't.

Consider a 10 volt voltage source having a 50 ohm source resistance,
feeding a 50 ohm resistive load. Power at the load is 0.5 watt, is it not?

Reduce the source impedance to 10 ohms.

Now what is the power dissipated in the load?
Is it greater or less than it was when the source and load impedances
were matched?

Roy Lewallen, W7EL

On May 26, 1:42 pm, walt wrote:
Hi Keith,

Sorry, OM, but you still misunderstand various aspects of RF power amp
operation.

First, the power supply is not the limiting factor concerning plate
current. The grid drive is what determines the plate current, and thus
the output power.

Of course the grid drive is one of the factors which controls the
current flowing in the load.

But the power supply is also one of the limiting factors. Reducing
the power supply voltage below that which is necessary to cause the
desired current to flow in the load will reduce the power output.
Similarly, increasing the load resistance will eventually raise it to
the point where the voltage is no longer adequate to cause the desired
current to flow.

Second, the tank circuit is an energy storage device that isolates the
non-linear input from the linear output. That the output is linear is
because the voltage and current are in phase at the output of the tank
circuit.

Can one not have a linear circuit where the current and voltage are
not
in phase? Also, if one loads any tank circuit with a resistance, the
output current and voltage will be in phase and if it is loaded with
a
reactance, they won’t be.

The effect of the energy storage of the tank results in the
tank becoming the source of the energy appearing at the output.

Yes, but that does not make the output independent of the input.

Third, the action of plate resistance Rp occurs only in the formation
of RL, and has no further effect on any action downstream of the input
of the tank circuit. Thus, it has no bearing on the development of the
conjugate match that occurs at the junction of the tank output and the
input of the transmission line.

I do not understand what is being said here.

Fourth, as I said earlier, the the action of the bench power supply
that you presented in no way models the action of the RF power
amplifier. Furthermore, you are incorrect when you say that when
varying the load in either direction causing the power deliver to
decrease there is no conjugate match. In saying what you did violates
the theorem of Maximum Transfer of Power.

The definition I use for conjugate match is one where the source
impedance is the complex conjugate of the load impedance. When this
situation occurs between linear networks, maximum power is transferred
between the networks.

None-the-less, just because maximum power is being transferred between
two networks does not mean they are complex conjugates of each other.
This is demonstrated with the non-linear behaviour of the bench power
supply example. Maximum power is transferred but the source and load
impedance are not complex conjugates.

Fifth, as I stated earlier, when the reactance appearing at the input
of the load (the transmission line with reflections) is canceled by
the opposite reactance introduced by the pi-network tuning capacitor,
the output impedance of the source (the tank circuit) is the conjugate
of the line-input impedance. If you cannot accept this as fact you
have a problem.

Perhaps I am not computing the impedances correctly. Let us see if I
have done so for the following example.

Consider a generator constructed of current source in parallel with
a resistor, driving a PI network, connected to a load.

generator filter load
6.945uH
+-------+------- ----+---/\/\/\/---+---- ---+
| | | |1.398 |
+---+ \ | | nF \
3.75 | I | /8000 ----- ----- / 50 ohm
MHz | | \ ----- ----- \
+---+ / |295.5 | /
| | | pF | |
+-------+------- ----+-------------+---- ---+

Looking into the input of the filter, then impedance is 1500 ohms.
This is the load applied to the generator and is computed by
applying the rules for series and parallel components to
the 50 ohm load, and the two capacitors and inductor in the PI
network.

It is, I hope, generally accepted that the generator will have an
output impedance of 8000 ohms.
The output impedance of the filter is computed by applying the
rules for series and parallel components to the 8000 ohm
generator impedance and the 3 components in the filter.
The result is 58.00 /_ 68.60 ohms.

Note that the component values were taken from a PA design where
the desired load for the tube was 1500 ohms. And 8000 is not an
unreasonable slope for the plate E-I curve of a tube.

This has not resulted in a conjugate match.

Sixth, your understanding of the effect of the reflected wave on the
source wave is flawed. The non-linearity of the plate current when the
conduction time is less than 360° has no relation to the action
downstream of the input to the tank circuit, because from that point
on the voltage current relationship is linear. If you cannot accept
this as fact you have still another problem.

It is, perhaps, this claim of isolation that is most strange. It seems
quite at odds with the rules for connected networks.

Seventh, your belief that because there is a conjugate match at the
output of the tank there must be a conjugate match at the input of the
tank is also not true. The effect of the energy storage in the tank
isolates the non-linearity af the input from the linear operation at
the output, permitting a conjugate match at the output, while not
allowing it to occur at the input.

It was my understanding that in a sequence of connected linear
networks, if any connection exhibited a conjugate match, then they
all were conjugately matched. Is this not correct?
Are you saying that if a conjugate match is present between the line
and the antenna, it might not be present between the transmitter and
the line?

These seven comments are born out (proven) by the results of many
measurements I made using laboratory grade instruments, HP and General
Radio. If you check my record as a professional electrical engineer
regarding the measurements I've made that led to successful hardware
flying on various Earth-orbiting platforms, you must accept the
validity of the measurements I made on RF power amplifiers that prove
my position.

I quite believe your measurements. It is the conclusion that they
prove a conjugate match that I find impossible to accept. Both
because there are other situations that can lead to power behaviours
that may appear similar to the power behaviour of a conjugate match
and the method proposed for computing source impedance is quite at
odds with linear theory.

But the quality of the measurements suggest it is worthwhile to
explore other explanations.

....Keith

On May 26, 6:20*pm, Roy Lewallen wrote:
Richard Harrison wrote:
Keith Dysart wrote:
"For the most part, "maximum power transfer is just an interesting
ideosyncracy of linear circuit theory."

In the world of 50 and 60 Hz, we don`t want all the power plant can
supply when we flip on a light switch.

The RF world is usually different.

Maximum power transfer only occurs when source and load match
conjugately, and the match proves the load and source impedances are
equals. It is well known and easily shown that a match results in
maximum power transfer.
. . .

It's also easily shown that it doesn't.

Consider a 10 volt voltage source having a 50 ohm source resistance,
feeding a 50 ohm resistive load. Power at the load is 0.5 watt, is it not?

Reduce the source impedance to 10 ohms.

Now what is the power dissipated in the load?
Is it greater or less than it was when the source and load impedances
were matched?

Roy Lewallen, W7EL

But Roy, consider that the source resistance remains constant at 10
ohms. Then what load resistance will absorb the most power? The answer
is 10 ohms. Any value of load resistance greater or less than 10 ohms
will result in less power delivered. I don't believe it's fair to
change the source resistance when dealing with the Maximum Power
Transfer Theorem.

In your example with a source resistance of 10 ohms and a load
resistance of 50 ohms the power delivered will be 1.39 watts. But when
the load resistance is 10 ohms with the same source resistance the
power delivered is 2.5 watts. As I said above, if the load resistance
is either greater or less than 10 ohms the power delivered will be
less than 2.5 watts. Thus when the source resistance is constant the
maximum power will be delivered when the load is matched to the
source.

Nes pa?

Walt

walt wrote:

But Roy, consider that the source resistance remains constant at 10
ohms. Then what load resistance will absorb the most power? The answer
is 10 ohms. Any value of load resistance greater or less than 10 ohms
will result in less power delivered. I don't believe it's fair to
change the source resistance when dealing with the Maximum Power
Transfer Theorem.

In your example with a source resistance of 10 ohms and a load
resistance of 50 ohms the power delivered will be 1.39 watts. But when
the load resistance is 10 ohms with the same source resistance the
power delivered is 2.5 watts. As I said above, if the load resistance
is either greater or less than 10 ohms the power delivered will be
less than 2.5 watts. Thus when the source resistance is constant the
maximum power will be delivered when the load is matched to the
source.

Nes pa?

Walt

Of course, I know that, and I would hope anyone with even very basic
electrical circuit analysis knowledge does. And anyone with that
knowledge should state as you have,

"FOR A GIVEN SOURCE IMPEDANCE, maximum power transfer occurs when the
source and load impedances are matched (i.e., the load impedance is the
complex conjugate of the source impedance)," which is true.

But the statement which was made was that "Maximum power transfer occurs
when the source and load impedances are matched." This is NOT true, as
the example demonstrates.

It's an important distinction. Instead of declaring what's "fair" and
what isn't with regard to changing source and load impedances, the
maximum power transfer theorem should be stated correctly, in a way
which makes it true.

Roy Lewallen, W7EL

On May 26, 1:19*pm, Cecil Moore wrote:
On May 26, 9:17*am, Cecil Moore wrote:

*If reflected energy is not allowed to reach the source, why
does the source impedance matter at all?

Continuing this thought thread - Assuming 50 ohm coax from the source
containing a forward traveling wave and no reflected wave, i.e. an SWR
of 1:1 on 50 ohm coax, what it to prohibit us from drawing our system
box through that piece of coax and considering the signal emerging
from that piece of coax to be the linear source signal which is
obviously associated with a V/I = 50 ohm impedance?
--
73, Cecil, w5dxp.com

If you are uninterested in source impedance (and many people seem
to be much more concerned with it than they need to be), then
by all means do not consider it, do not specify it, do not attempt
to compute it or measure it and do not make statements about what
the source impedance is.

But if source impedance is of concern for a particular application,
then please do compute and measure it properly.

....Keith

On May 26, 8:53*pm, Keith Dysart wrote:
It was my understanding that in a sequence of connected linear
networks, if any connection exhibited a conjugate match, then they
all were conjugately matched. Is this not correct?

The theorem requires linear *lossless* networks which do not exist in
reality, i.e. networks containing only reactances. Therefore an
*ideal* system-wide conjugate match cannot exist in reality just as a
lossless transmission line cannot exist in reality. In low-loss
systems, we can only achieve a system-wide near-conjugate match with
an ideal conjugate match existing at one point, e.g. the Z0-match
point where reflected energy flowing toward the source is eliminated.

Are you saying that if a conjugate match is present between the line
and the antenna, it might not be present between the transmitter and
the line?

Yes, speaking for me, in the real world, it is easy to prove that the
system-wide impedance looking in one direction is not always exactly
the conjugate of the impedance looking in the other direction. Thus
the "maximum power transfer" assertion has to be modified to "maximum
*available power* transfer". In the real world, ohmic and dielectric
losses reduce the power available to be delivered to the load.

It's easy to see. Let's say we have a completely flat 50 ohm system;
50 ohm source, 50 ohm coaxial feedline, and 50 ohm antenna. Now assume
we install an antenna tuner between the source and the feedline that
exhibits some series impedance and we adjust the tuner such that the
source sees 50 ohms. At the output of the tuner looking toward the
antenna, we will see 50 ohms. Looking back through the tuner toward
the source, we will see the tuner impedance in series with 50 ohms.
That proves it is not an *ideal* (lossless) conjugate match although
it may be considered to be a near-conjugate match, as close as we can
come in the real world.

What I don't know is how close a real-world conjugate match has to be
to an ideal lossless conjugate to be called a "conjugate match". A
purist might argue that an ideal conjugate match cannot exist in
reality. A realist might argue that if we are within 10% of an ideal
conjugate match, then it is a real-world conjugate match, by
definition.

Note that I am not speaking for Walt here, just for myself.
--
73, Cecil, w5dxp.com