"Richard Clark" wrote in message
...
On Mon, 06 Dec 2004 19:03:47 -0800, Roy Lewallen
wrote:
I never did quite get clear about your thesis. Would you mind restating
it?

Source Z matters.

What is the source Z of a solid state power amplifier, or even a tube
amplifier?

73,

Frank

Richard Clark wrote:
On Mon, 06 Dec 2004 19:03:47 -0800, Roy Lewallen
wrote:

I never did quite get clear about your thesis. Would you mind restating it?


Source Z matters.

Guess I didn't misunderstand after all -- it actually was so vague as to
be meaningless. Thanks for the elaboration.

Roy Lewallen, W7EL

"Richard Clark" wrote:
Source Z matters.

The *magnitudes* and *phases* of Vfor and Vref are affected by Zs as
described by Chipman. But I don't find anything in Chipman's book to
indicate that the *ratio* of Vmax to Vmin (VSWR) is affected by Zs.

Perusing all the references to VSWR in Chipman's book, you will find
that the source is not mentioned at all. Only the load reflection
coefficient
and the transmission line characteristics are needed to calculate VSWR.
--
73, Cecil http://www.qsl.net/w5dxp

Perusing all the references to VSWR in Chipman's book, you will find
that the source is not mentioned at all. Only the load reflection
coefficient
and the transmission line characteristics are needed to calculate VSWR.

===================================

Cecil, the trouble with 'bibles' is that they are so easily misquoted.
It's always better to rely only on your 'own' knowledge.

Only the MAGNITUDE of the reflection coefficient is needed to calculate SWR.
The phase angle is superfluous.

Nothing else whatever need be known about the line. Not even Zo, the
terminating impedance, and certainly not the generator impedance.

Conversely, the SWR will tell you virtually nothing about what's going on on
the line until you include and add to it what you already know anyway. You
can't even work back to find the reflection coefficint because of the loss
of the angle information.

The reflection coefficient is of no use to anybody without its angle,
except, of course to calculate the SWR.

Abolish SWR meters!
---
Reg.

On Tue, 07 Dec 2004 13:02:01 GMT, "Frank"
wrote:
What is the source Z of a solid state power amplifier

HI Frank,

Commonly 1.5 to 3 Ohms resistive transformed to 35 Ohms to 70 Ohms at
the Connector.

or even a tube amplifier?

Much greater variation here, X KOhms resistive transformed to 50 Ohms
at the connector.

Such are ballpark figures, as an average over a full cycle, at rated
power, for Class AB operation in a Push-Pull configuration. This
typically results in an efficiency on the order of 40% to 60%.

The nut of the matter about "Source Z matters" is that if your source
were at either of those untransformed Zs that are native to
transistors or tubes, then almost all their power would be reflected
back into them at the antenna connector's connection to a 50 Ohm
antenna system.

The argument of the matter about "Source Z matters" is that if your
source were at either of those untransformed Zs that are native to
transistors or tubes, then reflections from the load (once you got
some power into line) would encounter this same massive mismatch and
re-reflect. There is a naive argument here (all too common) that this
is "exactly" what happens. My pointed observation to those statements
is "why would anyone need a tuner then?"

The refinement of the matter about "Source Z matters" is that if your
source were at either of those untransformed Zs that are native to
transistors or tubes, then with any mismatch at the load you haven't
got a clue what power is being applied OR reflected. This is called
the Mismatch Uncertainty. It is another indicator of the failure of
the argument mentioned in the previous paragraph.

The relevance of the matter about "Source Z matters" here is that the
references that Bob used to measure and model line loss supports this
thesis. It presents an opportunity to observe how a line would suffer
additional loss through being mismatched at both ends. In this
regard, it would be due to the fictive argument for Source Z being
very much lower or very much higher than 50 Ohms (in other words,
lacking the transform circuitry commonly found in commercial gear).
When the loss is not observed, the fiction is shown.

73's
Richard Clark, KB7QHC

Hi Richard,

With solid state power amplifier design; the criteria was always that you
must present an impedance, to the output devices, such that the desired
output power is delivered to the load (while not exceeding device
dissipation). Any attempt to optimally match the load to the source
impedance will result in over-dissipation, and probable destruction of the
source device -- probably by excess collector/drain current. If you
remember, Motorola used to publish Smith charts of the output impedance for
their power amplifier devices. Talking to one of Motorola's design
engineers; I asked "How do you derive these Charts". His answer was; "We
use a matching network and adjust it for the required output power, then
measure the input impedance of the network. The complex conjugate of this
impedance is then defined as the source Z". The fact is these data are not
the actual source Z of the device, but are probably considerable higher. I
don't remember anybody actually trying to measure the large signal S
parameters of solid state devices.

I seem to remember that tube amplifiers were designed based on the source
impedance calculated as 2Vp/Ip, (Where Vp is the plate voltage, and Ip the
plate current), and have no idea how, or if, it relates to the actual source
Z of the device. Anyway, I am not convinced that source Z is important.
Where I think some confusion may have come from is Hewlett Packard's 12 term
error correction analysis derived for vector network analyzers. Here source
Z is important because measurements are made in both directions.

I have some conceptual problems with standing waves, and reflected power,
although I know that the solution to the wave equation shows a forward and
reverse traveling wave. Both with uniform plane waves, and in wire
transmission lines. Transmission lines can also be analyzed as a simple
passive network without regard to "Reflected power".

I am sure you will rip my comments to shreds, that's ok, as I may learn
something.

73,

Frank


"Richard Clark" wrote in message
...
On Tue, 07 Dec 2004 13:02:01 GMT, "Frank"
wrote:
What is the source Z of a solid state power amplifier

HI Frank,

Commonly 1.5 to 3 Ohms resistive transformed to 35 Ohms to 70 Ohms at
the Connector.

or even a tube amplifier?

Much greater variation here, X KOhms resistive transformed to 50 Ohms
at the connector.

Such are ballpark figures, as an average over a full cycle, at rated
power, for Class AB operation in a Push-Pull configuration. This
typically results in an efficiency on the order of 40% to 60%.

The nut of the matter about "Source Z matters" is that if your source
were at either of those untransformed Zs that are native to
transistors or tubes, then almost all their power would be reflected
back into them at the antenna connector's connection to a 50 Ohm
antenna system.

The argument of the matter about "Source Z matters" is that if your
source were at either of those untransformed Zs that are native to
transistors or tubes, then reflections from the load (once you got
some power into line) would encounter this same massive mismatch and
re-reflect. There is a naive argument here (all too common) that this
is "exactly" what happens. My pointed observation to those statements
is "why would anyone need a tuner then?"

The refinement of the matter about "Source Z matters" is that if your
source were at either of those untransformed Zs that are native to
transistors or tubes, then with any mismatch at the load you haven't
got a clue what power is being applied OR reflected. This is called
the Mismatch Uncertainty. It is another indicator of the failure of
the argument mentioned in the previous paragraph.

The relevance of the matter about "Source Z matters" here is that the
references that Bob used to measure and model line loss supports this
thesis. It presents an opportunity to observe how a line would suffer
additional loss through being mismatched at both ends. In this
regard, it would be due to the fictive argument for Source Z being
very much lower or very much higher than 50 Ohms (in other words,
lacking the transform circuitry commonly found in commercial gear).
When the loss is not observed, the fiction is shown.

73's
Richard Clark, KB7QHC

Richard Clark wrote:

This is called
the Mismatch Uncertainty.


The relevance of the matter about "Source Z matters" here is that the
references that Bob used to measure and model line loss supports this
thesis. It presents an opportunity to observe how a line would suffer
additional loss through being mismatched at both ends. In this
regard, it would be due to the fictive argument for Source Z being
very much lower or very much higher than 50 Ohms (in other words,
lacking the transform circuitry commonly found in commercial gear).
When the loss is not observed, the fiction is shown.

"It" should be called Grammatical Uncertainty.

73, AC6XG

On Tue, 07 Dec 2004 18:57:25 GMT, "Frank"
wrote:

"We
use a matching network and adjust it for the required output power, then
measure the input impedance of the network. The complex conjugate of this
impedance is then defined as the source Z". The fact is these data are not
the actual source Z of the device, but are probably considerable higher. I
don't remember anybody actually trying to measure the large signal S
parameters of solid state devices.

Hi Frank,

I've heard variations of this before, and other's admonitions that
Motorola admitted to a huge specification mistake in the early 90s and
had since mended their ways. When I asked for these updated
references, I ended up quoting verbatim from those mended teachings,
that, yes, Source Z has always been what was specified before
(...1990s), it was the same then (1990s), and it is the same now
(1990s...).

I've just returned from a nanotech seminar this afternoon whose
subject was organic thin film transistors. Dr. Daniel Frisbie -
Depts. of Chemical Engineering and Mat. Science - University of
Minnesota, offered that this new generation of research confirmed that
the Resistance of the transistor channel (similar to a MOSFET) easily
dominated all other sources of impedance. They also tested for
junction offsets (valence band - conduction band potentials) and found
they were negligible. The electron mobility wasn't the hottest thing
going (semiconducting carbon nanotubes easily dominate), but there
were no surprises. One of the EEs in the crowd easily allowed the
OTFTs showed no chemical/physical/electrical departures from
expectations (except for his concern for Schottky bias).

The technique you describe above is called a transfer standard.
Unless there is some mysterious shift in the space-time continuum to
account for this operation being invalid, it fully and accurately
describes the unit under test. Most arguments that lean on this
indirect measure being suspect would have us counting electrons
instead of using an Ammeter. Then we would argue about the counter
and its incapability of being a direct measure, but simply another
abstraction. Inevitably the arguments spiral down to the retort "you
are not going to change my mind."

I am already in the middle of the science that does real electron
counting, literally, where one can find what is called the Coulomb
barrier. For carbon nanotubes, things are so small that one electron
in a "wire" cannot allow another in with it to share the conductor.
Nothing like that is going on in our rigs.

73's
Richard Clark, KB7QHC

Hi Richard, thanks for your comments. My contacts with Motorola were in the
late 80s, so does put it in the correct time frame, and does not surprise
me. I know I thought of it as a not very elegant method. The particular
device I was thinking of was a dual push-pull (could have been parallel)
module designed for about 200 - 500 MHz, at about 50 W. As far as I am
concerned Motorola has gone down hill since they used to produce those thick
RF device data books. Not to mention 4DTV. During that same period
everybody was using a technique known as "Load-pull" for power amplifier
design. I was also involved, though not very deeply, in the design of 100 W
to 1 kW HF solid state linear amps, where I was told the same story about
not attempting to actually match the bipolar devices, but simply present an
appropriate impedance to obtain the output power; otherwise the device
parameters will be exceeded. I am far from an expert in the field of power
amplifier design, but it would be interesting to know if high power
transistors are now characterized by large signal S parameters. This may
sound really dumb, but how about feeding 100 W back into a transistor
amplifier, and measuring the return loss. It would at least give you the
large signal magnitude of S22.

You are starting to loose me when it comes to semi-conductor physics, as it
was not a field that I was especially interested in. I think the only
journals that I may have read about "nanotubes" may have been Scientific
American. I have also never had any experience with power FETs.

73,

Frank


"Richard Clark" wrote in message
...
On Tue, 07 Dec 2004 18:57:25 GMT, "Frank"
wrote:

"We
use a matching network and adjust it for the required output power, then
measure the input impedance of the network. The complex conjugate of this
impedance is then defined as the source Z". The fact is these data are
not
the actual source Z of the device, but are probably considerable higher.
I
don't remember anybody actually trying to measure the large signal S
parameters of solid state devices.

Hi Frank,

I've heard variations of this before, and other's admonitions that
Motorola admitted to a huge specification mistake in the early 90s and
had since mended their ways. When I asked for these updated
references, I ended up quoting verbatim from those mended teachings,
that, yes, Source Z has always been what was specified before
(...1990s), it was the same then (1990s), and it is the same now
(1990s...).

I've just returned from a nanotech seminar this afternoon whose
subject was organic thin film transistors. Dr. Daniel Frisbie -
Depts. of Chemical Engineering and Mat. Science - University of
Minnesota, offered that this new generation of research confirmed that
the Resistance of the transistor channel (similar to a MOSFET) easily
dominated all other sources of impedance. They also tested for
junction offsets (valence band - conduction band potentials) and found
they were negligible. The electron mobility wasn't the hottest thing
going (semiconducting carbon nanotubes easily dominate), but there
were no surprises. One of the EEs in the crowd easily allowed the
OTFTs showed no chemical/physical/electrical departures from
expectations (except for his concern for Schottky bias).

The technique you describe above is called a transfer standard.
Unless there is some mysterious shift in the space-time continuum to
account for this operation being invalid, it fully and accurately
describes the unit under test. Most arguments that lean on this
indirect measure being suspect would have us counting electrons
instead of using an Ammeter. Then we would argue about the counter
and its incapability of being a direct measure, but simply another
abstraction. Inevitably the arguments spiral down to the retort "you
are not going to change my mind."

I am already in the middle of the science that does real electron
counting, literally, where one can find what is called the Coulomb
barrier. For carbon nanotubes, things are so small that one electron
in a "wire" cannot allow another in with it to share the conductor.
Nothing like that is going on in our rigs.

73's
Richard Clark, KB7QHC

On Wed, 08 Dec 2004 01:25:07 GMT, "Frank"
wrote:

I was told the same story about
not attempting to actually match the bipolar devices, but simply present an
appropriate impedance to obtain the output power; otherwise the device
parameters will be exceeded.

Hi Frank,

There used to be an old, old song: "Yes dear you can go swimming, but
don't go near the water."

Even at DC, you cannot design to the capacity of a transistor, because
the combination of all capacities exceed the "safe operating area."
However, this does nothing to actually change any noted specification.

I've never seen ANY power amplifier for retail trade conjugately
matched to its Source Z. But then I have never seen ANY amplifier for
retail trade designed to be low noise, low distortion, high stability,
or any of the more common qualities that "could be" designed in, if it
weren't for cost and the perception of no particular boon to the
purchaser. Who needed low distortion when you could throw a cheap
filter on the output? Who need low noise when atmospherics dominated
such issues? Who needed stability when the monkey twisting the knob
would correct it as a form of entertainment? Safety margin? Add a
fan to the heatsink - $pecial option.

This may
sound really dumb, but how about feeding 100 W back into a transistor
amplifier, and measuring the return loss. It would at least give you the
large signal magnitude of S22.

This was done decades ago - it is called an active load. I used to
calibrate them too. Guess what, it was specified and it met spec at
50 Ohms (and at least 100W).

73's
Richard Clark, KB7QHC