On 12 Aug 2003 18:02:19 GMT, (JDer8745) wrote:

He sed:

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

---------

THIS IS ABSOLUTELY CORRECT!

73 Jack

Hi Jack,

Hmm, the world of accurate measurement must be wrong then. :-)

It is correct that into a matched load, it makes little difference -
that is not the subject at hand, and as I have said, it has already
been demonstrated twice.

To this point I have seen no counter demonstrations, nor counter
proposals, nor counter argument (no, Jack, yours is not an argument),
nor conflicting bench data. What I have seen are sweeping statements
without any supporting evidence. Given the amateur preference for the
snuggly comfort of illusion, I suppose none of this will change. Not
that I care, it does provide me entertainment (right now in fact) when
astonished correspondents post their plight and are offered responses
of nostrums and head-bobbing. I would offer that it is a joke that
never grows tired - simply because so few would recognize they had a
problem in the first place. In fact, this second demonstration arose
through the naive investigation of a non-amateur. Too many amateurs
consider themselves above such bench activity and too sophisticated to
trod that path.

The flip side of the argument (and why it is so painfully ignored) is
that reveals that most rigs DO exhibit a Z of nearly 50 Ohms such that
this is rarely a problem. It also reveals a shortfall of bench
experience in amateur construction. There was a time when many more
suffered this because they built their own transmitter instead of
passing a credit card across the display case to a sales clerk.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
To this point I have seen no counter demonstrations, nor counter
proposals, nor counter argument ...

Not unusual since your above deadline for counter demonstrations,
counter proposals, and counter arguments was 66 minutes from the
time you made the original posting. :-)

You are in a room with a 150 ohm (lossless) transmission line coming
through a hole in the wall and with a 50+j0 ohm load in the center of
the room. Are you telling us that the SWR is not (1+|rho|)/(1-|rho|)?
--
73, Cecil http://www.qsl.net/w5dxp



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On Tue, 12 Aug 2003 14:13:44 -0500, W5DXP
wrote:

Richard Clark wrote:
To this point I have seen no counter demonstrations, nor counter
proposals, nor counter argument ...

Not unusual since your above deadline for counter demonstrations,
counter proposals, and counter arguments was 66 minutes from the
time you made the original posting. :-)

Hi Cecil,

I see you still live in a dimensional aberration where you experience
22 days as 66 minutes. You must be oxygen starved by now.

73's
Richard Clark, KB7QHC

(Tom Bruhns) wrote in message om...
(Dr. Slick) wrote in message . com...

But can you make a 50 Ohm dummy load with those specs that can
handle
300 Watts? The stays at 50 Ohms out to at least 200 Megs or so?


50 +/- what? What return loss are you shooting for in this 300W dummy
load? Do you really need 40dB, or is 30dB good enough? I believe
it's possible to bootstrap yourself into measurements that are far
more accurate than you'll need for what you are doing, and do it quite
economically if you don't count your time. But you ought to first ask
yourself just what accuracy you really need, and understand why.


+/- 5 ohms or so. Something that doesn't swing up to 65-70 ohms or
40 ohms.




And i'm still not sure what you mean by "calibrate your SWR meter
to the line". All the SWR meters i have seen are all for 50 Ohms.

Could you tell us the exact procedure?

Of course not; I know nothing about YOUR SWR meter. If you understand
how yours works, you should be able to see how to adjust it, though it
may not be worthwhile.


I didn't think you could tell us. I've never seen an SWR meter
that you could "calibrate" to 50 or 75 ohms, or less.


Slick

Egad.

Given only a line's characteristic impedance and the load impedance, I
can tell you exactly what the SWR is for a lossless line. For a lossy
line, I only need to know, in addition, the line's length and the amount
of loss per unit length. In no case do I need to know the source impedance.

If, as you insist, the source impedance affects the SWR on the line,
please provide an equation that gives the SWR on the line, with source
impedance being one of the variables. It's such a simple thing, surely
such an equation appears in one of the several references you cite. I
did notice that SWR doesn't appear in any of the titles or the quoted
passages, though, so you may have to dig a little.

And if Cecil's work leads to the conclusion that the source impedance
impacts the line's SWR, then it's wrong.

It is, for those who are interested, very easy to see intuitively why
the source impedance doesn't affect the SWR. Consider the situation that
occurs when the source is first turned on. A forward voltage wave
travels down the line toward the load. A reflected wave, whose magnitude
and phase are determined by the reflection coefficient at the load end
of the line, returns. If we stop time just as the reflected wave is
returning, we can calculate the SWR, so far, on the line, solely from
the ratio of the forward and reflected waves -- it's the interference
between these waves that create the standing waves. Turning time back on
again, the returning wave reflects off the source (assuming a source
mismatch), producing another forward wave. Let's watch this wave as it
travels toward the load, reflects, and returns. Exactly the same
proportion of this wave is reflected as for the original forward wave.
So, when this new forward wave reflects and its reflected wave returns,
we've got a total of two forward waves and two reflected waves. The
forward/reflected ratio of the second pair is exactly the same as the
forward/reflected ratio of the first pair -- it's the reflection
coefficient at the load end. So the ratio of the total forward wave to
the total reverse wave is the same for the first pair, the second pair,
and the sum of the two pairs. In other words, the second pair of waves
hasn't changed the SWR from what we calculated from the original pair of
waves. You can continue this observation for each forward-reverse pair,
and see that the SWR never changes (at least when observed when each
reflected wave just returns) from the original value. And the original
value was determined only by the load mismatch, not the source. The
source mismatch determines how big the total forward and reflected waves
end up being when all the reflections have died out to a negligible
value. But it has nothing to do with the forward/reverse ratio, which
determines the SWR.

Roy Lewallen, W7EL

Richard Clark wrote:
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

Sorry, it's not clear from what you've said just what you're trying to
match to what.

Truly, if you connect a 50 ohm load (be it a resistor, or some impedance
transformed by a transmission line, tuner, or other means -- makes no
difference) to a transmitter, and the transmitter's output impedance
isn't 50 ohms, there will be a mismatch at the transmitter output.

But who cares? Most transmitters are designed to work properly when
terminated with 50 ohms, but that doesn't at all mean that their output
impedances are 50 ohms. And it certainly doesn't affect the SWR on any
transmission line connected to the transmitter. If you were to discover
that your transmitter's output impedance were, say, 10 ohms and you
connected it to a 10 ohm load, you'd have a very unhappy transmitter.
All you have to worry about is presenting the transmitter with the load
it was designed to work into, not what the internal impedance of the
transmitter is.

Roy Lewallen, W7EL

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

Almost correct.

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

Roy Lewallen, W7EL




My point is that if the output impedance really was at a perfect
50 Ohms, then using a perfect 50 ohms transmission line, you can never
match to anything other than 50 ohms.

If the S22 is something other than 50 Ohms (usual case), then a
transformation via 50 ohm coax about a constant VSWR is possible, for
the purposes of matching to a not-quite-perfectly-50 ohms antenna.


Slick

Richard Clark wrote:
I see you still live in a dimensional aberration where you experience
22 days as 66 minutes.

I see that you still ignore the technical questions so I will repeat mine:
Are you saying that SWR doesn't equal (1+|rho|)/(1-|rho|)?
--
73, Cecil http://www.qsl.net/w5dxp



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Dr. Slick wrote:
I didn't think you could tell us. I've never seen an SWR meter
that you could "calibrate" to 50 or 75 ohms, or less.

The calibration of the SWR meter is controlled by the internal sampling
load resistor, the 'R' in Peter's V + IR equation. I have a home-brewed
SWR meter that measures SWR on both balanced 450 ohm feedlines and on
300 ohm feedlines simply by changing the internal load resistors.
--
73, Cecil http://www.qsl.net/w5dxp



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Had a look at the refs. I'm curious, did you actually read the
sentence that Roy wrote?

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 Tue, 12 Aug 2003 14:25:47 -0700, Roy Lewallen
wrote:
If, as you insist, the source impedance affects the SWR on the line,
please provide an equation that gives the SWR on the line, with source
impedance being one of the variables.

Hi Roy,

Your crafted requirement reveals the shortfall inherent in the
problem. It is distance based too, and without that discussion there
is no way to forecast what SWR or Power reading you would obtain from
simply knowing both the load and source's Z's. This is why it is
called Mismatch Uncertainty.

I have provided NBS and NIST documents both recently and in the past.
Recent offerings are obscure, as I have already admitted. The earlier
citations I provided were direct and to the point and serve as the
basis of the recent work. I have provided data that exhibits the
effect. I have provided the test protocol in how to achieve that
data. I have also described that this data is also, theoretically,
achievable through standard interference math also presented by me in
the past.

It takes little imagination to observe that there is a zone of
confusion that lies between two reflecting interfaces when the path is
not fully described. My data showed that path in one foot increments
of transmission line over an interval of a quarter wavelength or more.

We have been offered evidence of this Mismatch Uncertainty by Dr.
Slick if I am to trust his postings - be that as it may, because it
requires no further proof.

Simply put, bald assertions that SWR is unaffected when read between
two discontinuities is wrong without a concomitant description of all
paths leading to the SWR meter. This is a commonplace of interference
plain and simple. I have observed no one describing this detail
(except Dr. Slick).

As all this is part of the historical record entitled:
"The Cecilian Gambit, a variation on the Galilean Defense revisited"
I do not see how its repetition here brings anything new to the mix.

None the less, this recent example has been fun. :-)

73's
Richard Clark, KB7QHC