Richard Clark wrote:
How curious of you to have missed this pæan to your style:

Not curious at all, Richard. My Mother is in the hospital
with terminal leukemia.
--
73, Cecil, W5DXP

Richard,

Thank you very much for posting that reference to John Juroshek's
article. It happens to cover a topic very near and dear to my heart,
and I called John and we had a nice chat about it. In addition, I
told him where I saw the reference, and asked him if he would say that
the SWR on a line, in steady state excitation, with a source at one
end and a load at the other, depended on the source's source
impedance. He said it of course does not, and cannot understand how
you would have interpreted it that way.

Should I check with any of the other authors?

Cheers,
Tom

Richard Clark wrote in message . ..
On Tue, 12 Aug 2003 02:48:49 -0700, Roy Lewallen
wrote:

Almost correct.

The transmitter output impedance has no effect whatsoever on the line's SWR.

Roy Lewallen, W7EL


Hi Roy,

Entirely incorrect.

Transmitter output impedance that does not conform to transmission
line Z, when presented with a mismatched load through that line, adds
mismatch uncertainty in the form of an indeterminate SWR and
indeterminate Power to the load.

This has already been demonstrated twice. This has long been
documented with NBS/NIST references going back 4 decades. There is
nothing mysterious about it at all, and it conforms to the rather
simple principles of wave interference so poorly presented by Cecil in
months past.

The authoritative site:
http://www.boulder.nist.gov/div813/index.html

Direct reference:
"Juroshek, J. R.; A Direct Calibration Method for Measuring
Equivalent Source Mismatch; Microwave J., pp. 106-118;
October 1997

Obscure references:
http://www.boulder.nist.gov/div813/r...00S_n2nNet.pdf
"With vector measurements of the generator and meter reflection
coefficients Ãg and Ãm, respectively, the power of the incident
signal am can be related to the power of the source."

http://www.boulder.nist.gov/div813/r...FRad_ARFTG.pdf
which describes radiometer calibration (perhaps too exotic for this
group)
"tests are based on two assumptions. First, the network responds
linearly to our signal ( no power compression), and second, the
radiometer is sufficiently isolated from the source impedance."
...
"One of the assumptions made in deriving eq. (2) was that the
output from the radiometer is not dependent on the source
impedance. In the construction of the radiometer, two isolators
are inserted at the input of the radiometer to isolate the
radiometer from the source."
...
"The mismatch uncertainty depends strongly on the poorly known
correlation between uncertainties in the measurements of different
reflection coefficients, and so we use the maximum of the
uncertainties obtained by assuming either complete correlation or
no correlation whatsoever."

"Forthcoming Paper: Influence of Impedance Mismatch Effects on
Measurements of Unloaded Q Factors of Transmission Mode Dielectric
Resonators"
IEEE Transaction on Applied Superconductivity

"Analysis of Interconnection Network and Mismatch in the
Nose-to-Nose Calibration
Automatic RF Techniques Group , June 15-16, 2000 , Boston, MA -
June 01, 2000
"We analyze the input networks of the samplers used in the
nose-to-nose calibration method. Our model demonstrates that the
required input network conditions are satisfied in this method and
shows the interconnection errors are limited to measurement
uncertainties of input reflection coefficients and adapter
S-parameters utilized during the calibration procedure. Further,
the input network model fully includes the effects of mismatch
reflections, and we use the model to reconcile nose-to-nose
waveform correction methods with traditional signal power
measurement techniques."

As I mentioned, obscure references. However, given the impetus of
their discussion is long known (and that I have already provided the
original references they rely on), NIST presumes the investigators
already have that basis of knowledge.

73's
Richard Clark, KB7QHC

On 14 Aug 2003 13:17:40 -0700, (Tom Bruhns) wrote:

Richard,

Thank you very much for posting that reference to John Juroshek's
article. It happens to cover a topic very near and dear to my heart,
and I called John and we had a nice chat about it. In addition, I
told him where I saw the reference, and asked him if he would say that
the SWR on a line, in steady state excitation, with a source at one
end and a load at the other, depended on the source's source
impedance. He said it of course does not, and cannot understand how
you would have interpreted it that way.

Should I check with any of the other authors?

Cheers,
Tom


Hi Tom,

Feel free to do that. I cannot imagine I hold sway over that anyway.
Do you really need more proof, or is your question an honest enquiry
suggesting you accept the possibility that someone else may actually
stand with me?

You among the many have done more in less time. I can accept
negative, informed response. Can he explain my posting? That is the
more telling as it is MY statement, not your summary of it.

I am not looking to shift the goal posts during the game, the posting
contains the beginning and end of it. It stands alone, or it falls
because of its own errors, not those appended, removed, remodeled,
explained, or fancified through specious "debate." I find more
entertainment in bearding the complacency it meets.

I have seen my results dismissed. I hardly find it surprising, but
with repetition it seems those in chant mode are insecure with their
mantra. After all what purpose is there in saying it twice in a round
of three postings? (or 3 of 5, or 5 of 7....).

73's
Richard Clark, KB7QHC

On 14 Aug 2003 13:17:40 -0700, (Tom Bruhns) wrote:

Thank you very much for posting that reference to John Juroshek's
article. It happens to cover a topic very near and dear to my heart,
and I called John and we had a nice chat about it.

Hi Tom,

As an after thought, but not secondary in my mind (tho' certainly in
the heat of response). You are welcome. I am glad that even the
obscure references elicit a positive outcome regardless of how it
suits my thesis. THIS is the point of my writing (the rest is simply
the struggle of titanic ego).

73's
Richard Clark, KB7QHC

On Thu, 14 Aug 2003 14:56:27 -0700, W5DXP
wrote:

Richard Clark wrote:
You among the many have done more in less time. I can accept
negative, informed response. Can he explain my posting? That is the
more telling as it is MY statement, not your summary of it.

A couple of questions about your data. What kind of coax and
connectors are used for the BVT?

hardline of RG-58 dimension;
only two connectors, the gozinta, and the comesoutta (never changed
throughout any variation nor calibration).

What kind of wattmeter was
used for the readings?

Bird.


The load seems to be 50/3 = 16.67 ohms. I would like to see
the same data for a load of 50 ohms.

That is already discussed in the report.

Seems you are getting
the same resulting effect that I do (on purpose) when I vary
the length of my ladder-line while watching the 50 ohm SWR.
Your results may repeat every 1/2WL. What if you had gone
out to 20 feet instead of stopping at 15 feet?

I have no reason to think it would offer any change in a periodic
variation already in evidence.


One last thought. Did you consider common-mode current
possibilities?

Yes.

73's
Richard Clark, KB7QHC

W5DXP wrote in message ...

By definition. I wonder who invented that definition? It seems pretty
obvious that not all PA's are Z0-matched so they will always re-reflect
100% of the incident reflected power. But that is exactly what that
definition implies.


Your vocabulary is very confusing here, Cecil. "Incident"
usually refers to the forward power, so when you say "incident
reflected" it's extremely confusing.


Slick

Roy Lewallen wrote in message ...
Dr. Slick wrote:

Agreed. Then any mismatch loss from PA to the 50 ohm coax is
never measured at the meter. So we never really measure the reflected
power coming right out of the PA, even if we attach the meter directly
to it's output.

No "reflected power" comes out of a PA.

Roy Lewallen, W7EL

Maybe that why you can't measure it.


Slick

Roy Lewallen wrote in message ...

The observation that changing line length changes the measured SWR is
regularly reported in this newsgroup, and the explanation is as
regularly provided.

There are at least three ways this can happen.

1. The SWR meter is designed for an SWR that's different from the line
impedance. It's easy to show that this will result in different readings
for different line lengths. I've measured RG-58 at over 60 ohms
characteristic impedance, so this can happen even with a perfect 50 ohm
SWR meter and "50 ohm" line. In this case, changing line length isn't
really changing the line's SWR, just the meter reading.


But a 60 ohm transmission line transformation from a non-50 ohm
load will certainly change the SWR, as it won't be on the constant
VSWR circle anymore.



2. There's significant loss in the cable. In that case, the longer the
distance between the meter and the load, the better the SWR.


That's the obvious one.


3. There's current on the outside of the coax. This means that the
outside of the transmission line is actually part of the antenna. When
you change its length, it changes the effective length of the antenna,
which really does change the SWR. Current on the outside of the cable
can also get into a poorly shielded SWR meter and modify its reading.

And this is all in agreement with established theory. So you see, theory
does say you can change the SWR reading, and in some cases, the actual
SWR, by changing the coax length. But only under very specific
circumstances. When observations don't match theory, chances are
overwhelming high that either the observation is erroneous or
misinterpreted, or theory is being misapplied.

Roy Lewallen, W7EL



I believe the source of confusion is he


PA----+----50 ohm line----+SWR meter+----50 ohm line----+50 ohm dummy
load
1 2 3



The "+" are connector points. You folks are saying that as you
change the PA (source) impedance, that the SWR you read will remain
the same, even if the incident power changes due to the change in
reflected power at point 1.

This i can agree with, as no matter how much incident power makes
it past the impedance discontinuity at point 1, the system after this
point will theoretically always reflect the same ratio of reflected
power to incident.
But, if you place an SWR meter of the same impedance as the output
of the PA at point 1, you will definitely see a change in SWR at point
1 as you change the PA impedance, as you are changing the reference
impedance (center of Smith re-normalized). This is what i thought you
meant when you said "change the source impedance", but you meant to
say "change the source, but keep the reference impedance the same".

Understood, assuming this is what you guys mean.


Slick

Roy Lewallen wrote in message ...
If you ever do see an equation which shows transmission line SWR as a
function of source impedance, please let me know where you see it. I'll
add it to my list of untrustworthy sources.

A simple experiment could be set up to disprove it.

Roy Lewallen, W7EL




I believe we are both right, and there is simply a misunderstanding
here.

I believe the source of confusion is he


PA----+----50 ohm line----+SWR meter+----50 ohm line----+50 ohm dummy
load
1 2 3



The "+" are connector points. You folks are saying that as you
change the PA (source) impedance, that the SWR you read will remain
the same, even if the incident power changes due to the change in
reflected power at point 1.

This i can agree with, as no matter how much incident power makes
it past the impedance discontinuity at point 1, the system after this
point will theoretically always reflect the same ratio of reflected
power to incident.
But, if you place an SWR meter of the SAME IMPEDANCE AS THE OUTPUT
of the PA at point 1, you will definitely see a change in SWR at point
1 as you change the PA impedance, as you are changing the reference
impedance (center of Smith re-normalized). This is what i thought you
meant when you said "change the source impedance", but you meant to
say "change the source, but keep the reference impedance the same".

Understood, assuming this is what you guys mean.


Slick

W5DXP wrote in message ...


I was thinking about how you changed the impedance of your SWR
meter, and I doubt that simply changing the terminating resistors to
ground on both directional couplers is all you have to do.

I believe this because the SWR/power meter needs to be a Zo ohm
Thru, with a microstrip line of a certain dielectric thickness, and
particular width and spacing from the couplers. And you cannot change
these very easily.

Do you have a schematic for us to see?


Slick