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