On Fri, 03 Oct 2003 18:11:14 GMT, Richard Clark wrote:

On Fri, 03 Oct 2003 12:01:08 -0500, Cecil Moore
wrote:

Richard Clark wrote:
There are one of two possible explanations for your posting:
1. You have not obtained that copy of Chipman that you ordered.
2. You have not read it.
Of course, you can add a third, fourth or fifth... in complete absence
of Chipman's discussion if his material does not agree with your
interpretations.

Richard, you might be interested to know that HP's s-parameter ap note,
AN 95-1, page 22 under Transducer Power Gain, lists the power available
from the source as the (square of the magnitude of the source voltage)
divided by [one minus the (square of the magnitude of the source's complex
reflection coefficient)], i.e. |Vs|^2/(1-|rho|^2)=power available from
the source where presumably source-rho = (Zs-Z0)/(Zs+Z0)

Hi Cecil,

-sigh- even when you offer confirmatory recitations you still miss the
details. There are only 11 pages in Application Note 95-1 and the
material you describe appears on page 4 not 22.

The voltage from the generator is also portrayed in Fig. 3 entitled
"Flow graph of network of Fig. 2." Figure 2, of course, shows the
generator complete with Zs which most here deny exists, or dismiss as
immaterial to any discussion. This is due entirely to their speed
reading past their own sources' discussion that ALL DISCUSSION OF SWR
assumes the source matches the line it feeds. Such an explicit or
implicit relationship is fundamentally required, or the entire text
that they cite is rendered useless gibberish. The most garbled of
those proclamations is that the source Z has no bearing on line SWR.

This same flowgraph is present in many similar works (AN 95-1 is
hardly unique) and being presented early in the work (like Chipman's
similar observation of requiring source-line matching) is skipped so
that the reader (sic) can scrounge their favorite snippet of math and
remove it from its required context. Chipman also presents much the
same treatment in non S-Parameter discussion, but that is quite
obviously from the part unread by the great mass of so called
adherents to his discussion.

However, to give some flexibility to the discussion; such shortfalls
of understanding how SWR works is simply through lack of experience in
the matter. It is understandable when the usual approach to this
topic is taken by employing a transmitter that both specifies its
output at a Z of 50 Ohms and exhibits a Z of 50 Ohms. Given such a
source, the casual debater is lulled into the comfortable illusion of
having been born on third base thinking they hit a triple in the
debate against source Z (no, the count is three strikes).

Simply because they encounter no ill consequence of source mismatch is
NOT evidence of the source Z being immaterial to the process of
measuring SWR. Luck counts for nothing in debate - unless it is
admitted to. None here count themselves lucky - it would diminish
their sense of erudition.

I don't expect there will be any substantive discussion following this
that will change physics to conform to those illusions (my comments
here will not "change their minds").

73's
Richard Clark, KB7QHC

Richard, I'm dismayed with your statements above. Are you really serious? Or are
you just giving Cecil a bad time?

I've been grappling with your last email to me concerning the nature of the
source resistance of RF amps, and as with your statements above, I'm at a loss
as to how to respond, because we are 180 degrees apart on the source resistance
issue. I'm still going to respond to it, but right now I want to address the SWR
issue.

Richard, how can you possibly believe that the output impedance of the source
has any effect on the SWR on a transmission line? The only conditions
responsible for SWR are the Zo of the line and the ZL of the load--nothing else.
I've been bench measuring SWR for more than 50 years, beginning with using the
slotted line before more sophisticated machinery was available. It didn't matter
what the source impedance was, the SWR remained the same, whatever the source.
Ian told it like it is, and so does Walter C. Johnson in his "Transmission Lines
and Networks, Page 100, where he says:

"The steady state ratio Eplus/Eminus was determined in Eq 11 as the reflection
coefficient k...This ratio is determined only by the load and the line, not by
the generator. It is completely unaffected by the quantity kg = (Zg - Zo)/(Zg +
Zo), which is the reflection coefficient seen by an individual
backward-traveling wave as it reaches the generator terminals. ...the latter
affects the steady state solution only on its influence on the sending-end
voltage, i.e., through its influence on the magnitude of the entire solution."

Your reply comments, please.

Walt, W2DU

Just a comment.

Whereas it is true the SWR remains relatively constant along a relatively
low loss line, it is NOT true that the reflection coefficint remains
constant. Its phase angle (1/2 of the information it contains) varies in
proportion the distance from the termination.

On Fri, 3 Oct 2003 22:57:54 +0000 (UTC), "Reg Edwards"
wrote:

Just a comment.

Whereas it is true the SWR remains relatively constant along a relatively
low loss line, it is NOT true that the reflection coefficint remains
constant. Its phase angle (1/2 of the information it contains) varies in
proportion the distance from the termination.


A little further comment.

The magnitude of rho is always the ratio of reflected to forward voltage at
whatever whatever point it is measured on any lossless or non-lossless line. On
lossless line the magnitude of rho is constant along the entire line, but
decreases logarithmically with distance from the load,depending on the
attenuation of the line.

However, the phase angle of rho equals the angular difference between the
forward and reflected waves. Because they are traveling in opposite directions
the rate of angular change is twice the change in electrcal distance along the
line. Thus the phase angle of rho changes at twice the change in electrical
distance along the line, varying between zero and 180 degrees for every 1/4wl.

Walt, W2DU

On Fri, 03 Oct 2003 16:12:48 -0500, Cecil Moore
wrote:
One cannot verify anything about lossless lines on the bench.

You can't, that's for sure, and not even with a line so short you
couldn't measure its loss - so what's the point of arguing lossless?

So what Chipman
has to say is irrelevant to the problem you posed

Hi Cecil,

I have already provided quotes, chapter and verse that refute your
statement. No point in going further.

73's
Richard Clark, KB7QHC

On Fri, 03 Oct 2003 21:41:15 GMT, Walter Maxwell wrote:


Richard, I'm dismayed with your statements above. Are you really serious? Or are
you just giving Cecil a bad time?

That wouldn't take much to push Cecil off dead center.


I've been grappling with your last email to me concerning the nature of the
source resistance of RF amps, and as with your statements above, I'm at a loss
as to how to respond, because we are 180 degrees apart on the source resistance
issue. I'm still going to respond to it, but right now I want to address the SWR
issue.

Richard, how can you possibly believe that the output impedance of the source
has any effect on the SWR on a transmission line?

Stephen Adam of HP using Beatty describes it quite well. The data you
have by email and has been posted here demonstrates it equally well.
It takes no more than two resistors and a length of line to confirm or
deny. My data confirms it, absolutely no one has offered negative
evidence, simply denials.

The only conditions
responsible for SWR are the Zo of the line and the ZL of the load--nothing else.
I've been bench measuring SWR for more than 50 years, beginning with using the
slotted line before more sophisticated machinery was available. It didn't matter
what the source impedance was, the SWR remained the same, whatever the source.
Ian told it like it is, and so does Walter C. Johnson in his "Transmission Lines
and Networks, Page 100, where he says:

If Walter Johnson was not explicit about it, he was certainly implicit
about the requirement that the source match the line it is driving for
any discussion of SWR. This is so commonplace that no one ever
examines the situation where the source is a mismatch.

Too many here simply flip to the section in their favorite book about
SWR and wholly neglect the fundamentals that present this simple
requirement. I have presented quotes, chapter and verse from Chipman
where he explicitly says as much, and those who hold Chipman have
abandoned discussion rather than refute those quotes or accept their
error. As one scribbler put it I was not going to "change his mind."
I have no doubt of that, such a statement paints one into an extremely
embarrassing corner once having uttered it. One thing I learned as a
Metrologist is that I am always wrong, the significance is in the
degree of error, not the philosophy of sin and the rejection in
ignorance.

Any number of correspondents here "might" have the capacity to simply
repeat my methods and report their data; but absolutely none
demonstrate it. I might be so far in error the meter is pegged, but
the quality of "sneer review" absolves me of sin. ;-)

Hi Walt,

I await your response by email for our last round of discussion. What
is presented above is old material already discussed. There is
nothing new presented by me in it that has not found its way to your
mailbox.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
I have already provided quotes, chapter and verse that refute your
statement.

Here's a quote from Chipman. "These large reflection coefficients are an
example of the phenomenon of 'resonant rise of voltage' in series resonant
circuits... The large reflection coefficients are obtained only when the
reactance of the load impedance is of opposite sign to the reactance
component of the characteristic impedance." You posed a purely resistive Z0.
The "resonant rise of voltage" cannot happen with a purely resistive Z0.
Would you like to pose a complex Z0?
--
73, Cecil http://www.qsl.net/w5dxp



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Richard Clark wrote:
I have presented quotes, chapter and verse from Chipman
where he explicitly says as much, ...

And I have presented quotes, chapter and verse from Chipman,
that disprove your interpretations of what he said.
--
73, Cecil http://www.qsl.net/w5dxp



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Reg, that can't possibly be you. Someone has hijacked your e-mail.

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

Ian, it IS me! Please calm yourself.

Let me put what I said into somewhat different words.

SWR meters are designed to operate and provide indications of SWR, Rho, Fwd
Power, Refl.Power, on the ASSUMPTION that the internal impedance of the
transmitter is 50 ohms. It makes the same INCORRECT assumption as a lot of
people do. This should not be surprising because it was people who designed
it.

So SWR meters nearly always give FALSE indications about what actually
exists.

Perfectionists may be upset at the repercussions of this alarming statement.

PS: In the whole of his excellent 236-page exceedingly comprehensive
volume, Chipman, in 1969, makes not the slightest mention of SWR meters.
----
Reg, G4FGQ

Reg Edwards wrote:

SWR meters are designed to operate and provide indications of SWR, Rho, Fwd
Power, Refl.Power, on the ASSUMPTION that the internal impedance of the
transmitter is 50 ohms.

I believe that to be an incorrect statement, Reg. The assumption is that
a Z0 of 50 ohms exists and the transmission line is long enough to force
the ratio of V/I to be 50 ohms for the forward wave and the reflected wave.
The phase between the forward voltage and current is assumed to be zero.
The phase between the reflected voltage and current is assumed to be zero.
Given all those assumptions, the internal impedance of the transmitter is
irrelevant. I'm not saying all those assumptions are always met.

Put a 50 ohm dummy load on an SWR meter and feed it with a transmitter
of unknown source impedance. The SWR meter will always read 1:1 because
the dummy load forces the V/I ratio to be 50 no matter what the source
impedance. That's what the 50 ohm characteristic impedance of the
transmission is supposed to do to make the source impedance irrelevant.

PS: In the whole of his excellent 236-page exceedingly comprehensive
volume, Chipman, in 1969, makes not the slightest mention of SWR meters.

In 1969, virtually all ham transmitters had an adjustable pi-net output
so an SWR meter was not needed. When I started out as a ham in the 1950's,
just as many hams used 75 ohm coax as used 50 ohm coax, maybe more. The
pi-net output of a typical ham transmitter back then didn't care what the
Z0 was. I didn't own an SWR meter until the 1980's when I bought an IC-745.

In 1969, the "antenna tuner" was built into the transmitter. If wide-
range antenna tuners were built into transmitters today, there would be
little need for the SWR meter. I don't know of anyone who puts an SWR
meter between an SGC-230 and the antenna.
--
73, Cecil http://www.qsl.net/w5dxp



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--

SWR meters are designed to operate and provide indications of SWR, Rho,
Fwd
Power, Refl.Power, on the ASSUMPTION that the internal impedance of the
transmitter is 50 ohms.
=================================
I believe that to be an incorrect statement, Reg. The assumption is that
a Z0 of 50 ohms exists and the transmission line is long enough to force
the ratio of V/I to be 50 ohms for the forward wave and the reflected
wave.

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

But where have you hidden this remarkable transmission line which is long
enough to mug and hoodwink so-called SWR meters?

It does not exist!

Your argument falls flat at the start.

Reg, G4FGQ