On Mar 7, 9:35 pm, Owen Duffy wrote:
"walt" wrote in news:1173278086.390893.310040@
30g2000cwc.googlegroups.com:







On Mar 3, 4:37 am, Richard Clark wrote:
On Sat, 3 Mar 2007 00:10:21 +0000, Ian White GM3SEK
...
I've been reading this thread with interest, but the discussions
appear to be only academically related. On the other hand, I've made
measurements that prove the sailent points of these academic
discussions. These measurements were made since those reported in
Reflections 2, and will appear in Reflections 3. However, they are
available on my web page atwww.w2du.com. Go to 'Preview of Chapters
from Reflections 3' and click on Chapter 19A.

You may want to disregard the first portion of the chapter, which is
an epilog to Bruene's fiction concerning the conjugate match. The
pertinent portion here is that which reports in detail the step-by-
step procedure in measuring the output impedance of a Kenwood TS-830S
transceiver feeding a reactive-impedance load.

With a careful review of these steps I'm sure you'll find empirical
proof of the academics appearing in the previous posts.

Hi Walt,

I have read your document with interest, and will reread it a couple of
times yet.

The measurements are interesting, and on a first read, appear consistent
and in agreement with how things work as I understand it.

However, I don't believe any of your measurents actually reveal the
source impedance. You have shown the impact of the changed load on the
transmitter. You have demonstrated admirably the transformation of the
two external loads to the load seen by the plate(s), and you have shown
what the transmitter looks like from the antenna socket with a resistor
in place of the valves.

So, IMHO, the promise "The output source resistance of the amplifier in
this condition will later be shown to be 50 ohms" is not fulfilled.

It is my view that the statement "Because the amplifier was adjusted to
deliver the maximum available power of 100 watts prior to the resistance
measurement, resistance RLP looking into the plate (upstream from the
network terminals) is also approximately 1400 ohms" is not proven.

If we were to view the plate as a generator, and the pi network as a
lossless flexible variable impedance transformer, and you were to adjust
the pi network for maximum power transfer, that would imply that the
impedance loading the generator was the complex conjugate of its
equivalent series resistance... IF and ONLY IF the generator can be
accurately represented by an equivalent series circuit of a fixed voltage
generator and fixed equivalent series impedance.

The question is can the plate (or the whole transmitter for that matter)
be accurately replaced by an equivalent series circuit of a fixed voltage
generator and fixed equivalent series resistance (independent of load).

How would such a simple model deal with the case of a transmitter that at
maximum power output is close to voltage saturation (ie cannot develop
more output voltage) and close to current saturation (ie cannot develop
more output current)? These non-linear behaviours close to operating
point are not captured in a simple linear equivalent circuit.

Owen- Hide quoted text -

- Show quoted text -

Hi Owen,

Thank you for the insightful response.

First, let me say that although the average source resistance at the
plates appears to be 1400 ohms in the case I described, and IMHO I
believe it is, I'm not in the position of stating that is as a fact.
What I do claim as a fact is that when the transmitter is loaded to
deliver all available power to its load, the OUTPUT source resistance
(or impedance) at the output terminals is the conjugate of its load.
I'm differentiating between the conditions at the input of the pi-
network and those at the output, because the energy storage effect of
the network Q isolates the output from the input, such that the
conditions at the output can be represented by an equivalent Thevenin
generator. At the output terminals the conditions appearing at the
input are irrelevant, such as the shape and duration of the voltage
applied to the pi-network, as long as the energy storage Q is
sufficient to support a constant voltage-current relationship (linear)
at the output for whatever load is absorbing all the available power
from the network.

Thus, when all available power is delivered into a 50-ohm load the
source resistance at the output terminals is 50 ohms. Please also
review the later portion of Chapter 19, also available on my web page.
On those pages I report the results of measurements using the load-
variation method, which also shows the output source resistance to
equal the load resistance when the amp is delivering all its available
power.

Walt