On Mon, 6 Oct 2003 14:38:48 -0400, "Tarmo Tammaru" wrote:


"Walter Maxwell" wrote in message
.. .

This concept is foreign to me, so if I'm wrong I'd like to have some proof
that
the source impedance can have any influence on SWR.

Walt

Walt,

I don't think the source impedance has any effect on SWR. In fact I have
changed the source impedance and saw no change in SWR. But Since tha SWR
meter is a really dumb bunny, I wonder of the meter can be mislead by a
reactive source impedance that forces the current to be out of phase with
the voltage. Perhaps a case where the source and load both are reactive?

Tam/WB2TT

Tam,

I totally disagree with those who say SWR appearing on a mismatched transmission
line is dependent on the source impedance. If I understand Richard C correctly,
he claims with 'bullet-poof' certainty that SWR is dependent on the source
impedance. And if I understand Reg's earlier statement correctly, he shares
Richard's position. I asked Reg for clarification, but he has not yet responded.

Richard C, you suggest we step up to the bench and perform your experiment that
will prove you are correct. If you described this experiment to me earlier I
invoke my Alzheimer's excuse for not remembering it. So would you please repeat
it for my benefit? I'll be back at my Florida lab by Oct 22, and am anxious to
perform it.

And Richard H, thanks for the support. More than 50 years of lab and
professional work on transmission lines have never shown the source impedance to
have any effect on propagation along the line, other than to influence the
magnitude of the signal as it enters and propagates along the line.

Walt, W2DU

On Mon, 06 Oct 2003 21:10:25 GMT, Walter Maxwell wrote:
Richard C, you suggest we step up to the bench and perform your experiment that
will prove you are correct.

Hi Walt,

This is a misrepresentation of my work. I responded here that the
appearance of poor criticism suggests that my work is bulletproof
(among a spectrum of equal likelihoods) and my statement is a critique
of that shoddy work being offered as rebut to my data.

Further, I make no pretense that such an experiment will prove me
correct and I have offered on more than one occasion that someone with
care equal to mine could easily find data that refutes mine. I have
no illusions to being "correct" and have freely admitted that
everything I do contains error. However, I do, by training and
experience, exhibit those bounds of accuracy where others simply
caterwaul on that they need no lessons in the matter and further would
never "change their mind."

Now, if this appears to be backtracking, it is evident only to those
who will never attempt anything at the bench and have no capacity to
weigh their own sources of error - either of judgement or demonstrable
skill.

In conclusion, it is certainly an illusion to imagine that anything is
ever concluded. The best I can achieve is a confluence of thought
with one or several in educating rather exotic issues that lie outside
of the experience of many. There is nothing inherently common about
this, and is of interest to only those who aspire to accuracy, a very
limited audience.

The larger point that is germane to the whole of the audience is found
in the conduct of analysis, its support or its refutation. The
scientific community does not brook simple nay-saying and the shotgun
approach to cut-and-paste arguments offered as rebuttal. I have
described methods and results. My methods can be challenged, my
results can be shown irreproducible. I have offered tangible,
testable propositions, means, and results to which absolutely nothing
of equal merit has been put forward to provide a meaningful assault.
It is in that context that the appearance of a bulletproof
presentation has been suggested by me. :-)

The irony of my comments lies in the simple observation that this only
takes two resistors and a hank of line for one such test. The
magnitude of effort, as evidenced by those simple constraints suggests
that my critics are seriously skill impaired to offer honest testing.
I am content to stand above such midgets even if I have to stoop so as
to not make it so overwhelmingly and embarrassingly obvious.

73's
Richard Clark, KB7QHC

"Walter Maxwell" wrote in message
...
Tam,

I totally disagree with those who say SWR appearing on a mismatched
transmission
line is dependent on the source impedance.

Walter, I agree with you. But I am making a distinction between SWR and
*measured* SWR. People who think an SWR meter possesses magic properties
should look inside one. It takes one instantaneous sample of the NET voltage
V, and one instantaneous sample of the NET current I. It displays the vector
sum of
K(V + k2I)
and
K(V- k2I)

where K is the sensitivity, and k2 is chosen to make the second equation
equal to 0 for a 50 Ohm load. The approximations made in coming up with what
is printed on the meter scale assumes that for the forward wave the voltage
and current are in phase. I have seen descriptions of how these things work,
but no equations to back these up. I suspect one would start with the two
equations that I listed, but express I in terms of V and deltaZ, where
deltaZ is the deviation from 50 Ohms. K can arbitrarily be 1. I also suspect
that Bird, etc don't really want us to know that.

Tam/WB2TT

On Mon, 6 Oct 2003 20:52:24 -0400, "Tarmo Tammaru" wrote:


"Walter Maxwell" wrote in message
.. .
Tam,

I totally disagree with those who say SWR appearing on a mismatched
transmission
line is dependent on the source impedance.

Walter, I agree with you. But I am making a distinction between SWR and
*measured* SWR. People who think an SWR meter possesses magic properties
should look inside one. It takes one instantaneous sample of the NET voltage
V, and one instantaneous sample of the NET current I. It displays the vector
sum of
K(V + k2I)
and
K(V- k2I)

where K is the sensitivity, and k2 is chosen to make the second equation
equal to 0 for a 50 Ohm load. The approximations made in coming up with what
is printed on the meter scale assumes that for the forward wave the voltage
and current are in phase. I have seen descriptions of how these things work,
but no equations to back these up. I suspect one would start with the two
equations that I listed, but express I in terms of V and deltaZ, where
deltaZ is the deviation from 50 Ohms. K can arbitrarily be 1. I also suspect
that Bird, etc don't really want us to know that.

Tam/WB2TT

Well, Tam, I agree with you also, but your comments only relate to accuracy, not
whether the internal resistance of the source has any influence on the SWR. I'm
well acquainted with the various types of swr meters, the Bruene lumped-constant
directional coupler, for instance, or for a more professional example, the
HP-778D dual directional coupler that I use with an HP-8405A Vector Voltmeter in
my own lab.

The value of the source resistance can be any value, and its reflection
coefficient rho seen looking into the output can be any value from zero to one.
If the value is zero it simply means any reflected power reaching the output is
absorbed and if rho = 1all reflected power is re-reflected. With any combination
of the above the SWR on a mismatched line is the same. The only effect these
parameters have on the line is the magnitude of the signal being propagated. I
know this from years of experience, beginning with slotted lines, and from the
engineering literature. For example, Walter C. Johnson on Page 100 spells it out
specifically.

What I'd like to see is for those who say SWR is dependent on the source
impedance to show how and why this what I call 'misconception' can occur.

Walt, W2DU