The power explanation
 

Owen Duffy wrote:
"Breaking out of the previous thread to explore the "power explanation"
in a steady state situation:"

All OK as I see it.

Bird tells us that if you have significant standing waves, reflected
power is 10% or more of the forward power, and the ratio of reflected
power to forward power is then easily determined on the Bird Thruline
Wattmeter. Ratio of the reflected power to forward power is easily
converted to VSWR.

Bird supplies, charts, slide rules, and a formula for this conversion.

Bird confirms: "Power delivered to and dissipated in a load is given by:

Watts into load = Watts forward - Watts reflected."

Owen Duffy told us 100W is developed in 70 ohm load and the DC input
power of the transmitter is 200W.

Obviously 100W is dissipated in the transmitter and the efficiency is
50%.

Best regards, Richard Harrison, KB5WZI

The power explanation
 

"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 at www.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

The power explanation
 

On Wed, 07 Mar 2007 21:35:14 GMT, Owen Duffy wrote:

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.

Hi Owen,

Seems like the band has struck up another waltz.

For what it is worth, Walt would like:
Hi Richard,

Without my home computer I'm relatively helpless with no address library
available. I'd like to contact both Denny and Owen, but their email addresses
appearing in the Google venue are shortened--a big help.

So would you please give me both Denny's and Owen's email addresses.

Walt

It appears neither Denny nor Owen reveal their email here, so the only
alternative is for this appeal.

73's
Richard Clark, KB7QHC

The power explanation
 

On 7 Mar 2007 06:34:46 -0800, "walt" wrote:

I'm in a hotel in Jax, FL, unable to use my routine connections to
rraa, so I'm learning my way around in unknown territory here, and
hope to make a post that will appear.

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 at www.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.

Walt, W2DU

Another relay:

Hi All,

I have now been able to access this thread from my hotel room In Jax,
FL. I've read the posts with interest, but they appear to be only
discussions in academia. On the other hand, I have made measurements
that prove the salient points being discussed here.

My measurements include those made since those reported in Reflections
2, and are going to be available in Reflections 3. However, they are
presently available from my web page at www.w2du.com. Go to 'Preview
Chapters from Reflections 3' and select Chapter 19A. You may disregard
the first portion, which is intended as an epilog to Bruene's fiction
concerning the conjugate match. The pertinent portion here is a
detailed step-by-step description of the measurement procedure I
erformed on a Kenwood TS-830S transceiver with a reactive impedance
for its load.

A careful review of these steps will add empirical proof to the
academic enlightenment already evident in the previous posts.

Walt, W2DU

73's
Richard Clark, KB7QHC

The power explanation
 

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

The power explanation
 

Owen Duffy wrote:
"It is my view thatthe 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.."

The maximum power transfer theorem is a classic. It has been proven
countless times. It is explained by Terman in his 1955 opus on page 76.
It requires linearity in the area examined. A tuned circuit is often the
linearizer in an r-f amplifier. It eliminates harmonics of the
fundamental frequency so that Ohm`s law prevails across the output
terminals of the device. Thus, it is linear. It makes no difference that
ahead of the linearizer the power source is being pulsed so long as the
pulses don`t appear in the output. We don`t have pulses in the outputs
of our radios feeding our antennas.

When you have a conjugate match, the resistive parts of the source and
load are equal by definition.

Best regards, Richard Harrison, KB5WZI

The power explanation
 

"walt" wrote in
ups.com:

Walt,
....
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.

Ok, I think we are agreed that the measurements haven't directly
supported that belief.

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.

If it were a linear source and you delivered *maximum* (as opposed to
*all*) to the load, I agree that the load impedance is the complex
conjugate of the source impedance. That is essentially the Jacobi Maximum
Power Transfer Theoram.

The question is whether it is a sufficiently linear source to use that
model.

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, I have just re-read that section and note your measurements which
explored the delta V and delta I for small load variation (delta R) where
delta R is always negative, and calculated results.

Your results are interesting.

I have seen others report quite different results, and have found
differently myself on rough measurements, but I note your comments on the
sensitivity of the calculated Rs to tuning/matching which might reveal
why other tests disagree.

(It only takes one sound repeatable experiment that shows that the source
impedance is not the conjugate of the load to disprove the generality.)

On a practical note, the sensitivity discussed above does mean that if
your assertion about matching is true, it is unlikely that transmitters
are exactly matched.

My measurements have been on transistor PAs with broadband transformer
coupling to the load. The transmitters have had a lowpass filter with a
break point well above operating frequency between the transistors and
load. It is a different configuration, and although my measurements were
rough, they indicated different apparent source impedance at different
drive levels which questions the linear model for large signal operation,
especially for modes with varying amplitude such as SSB telephony.

Owen

The power explanation
 

Owen Duffy wrote:
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).

Can a real-world dynamic source impedance be
independent of load?
--
73, Cecil http://www.w5dxp.com

The power explanation
 

Owen Duffy wrote:

SNIPPED

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).

SNIPPED

The answer is NO!!

Power Amplifiers are not linear devices! [Regardless of manufacturer's claims].

My AL-80B puts out ~850 watts with ~1300 watts input. IF a conjugate match
existed the output would be ~650 watts. The Zo of the 3-500 varies depending on
the phase of the pulse signal. The amplifier provides a pulse of energy into the
tuned circuit, tank circuit, tuner, antenna, where the reactances maintain the
current/voltage under resonant conditions.

My understanding is that reflected energy is also coupled into the tuned
circuits. The active device, power amplifier, may be cutoff, saturated, or
somewhere on the active load line. The energy in the tuned circuit will increase
the Vmax and/or Imax depending on the circuit QL. This increase in stored energy
provides the extra stress on the active device. If the QL 10, nominal design
value, then 90% of the reflected energy is re-reflected back towards the load.
The missing 10% produces heat in the tuned circuit.

Devices that operate from saturation to cutoff are by definition NON-LINEAR.

The tuned circuits store both forward and reflected energy. Ultimately all the
power is radiated, either as a rf field or as heat.

The power explanation
 

On Wed, 07 Mar 2007 20:27:10 -0500, Dave wrote:

Ultimately all the power is radiated, either as a rf field or as heat.

Hi Dave,

Well, having said that, it was hardly worth constraining the rest of
the discussion with linearity, SWR, efficiency, pulses, Q, cut-off,
saturated, tube or transistor.

73's
Richard Clark, KB7QHC