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

"Cecil Moore" wrote in message
...
Richard Harrison wrote:
In the usual h-f transmission line, Zo appears as an Ro.

RG-174 has about 6dB loss per 100ft on 12m. Its Z0 is equal
to Sqrt[(R+jXL)/(G+jXC)].

Does (R+jXL)/(G+jXC) really equal 2500 for RG-174 on 12m? The specs
say the Z0 of RG-174 is a nominal 50 ohms.

of course its not exactly 2500, otherwise there would be no loss. but its
close, maybe 2500+j10 or something like that. and even the resistive part
may not be exact, the nominal 50 ohms could be 45 to 55 depending on the
tolerances of the manufacturer.

On Mon, 06 Oct 2003 14:37:18 -0500, Cecil Moore
wrote:

I offered an experiment that might prove you right
... I suspect the above condition is representative of what you are
seeing in your measurements.

Hi Cecil,

Your memory of those measurements alternately gains clarity and fades
by the passage of each moment. I need no further examples, as flawed
or superlative as they may be, to support my thesis that stands by
simple resistive loads. Your gilding of the Lily and painting the
Rose is performed off the bench as a means to yet again force the
world into a speculation that your xeroxed page of Chipman responds
to. No further analysis is required, it has been performed and data
taken has demonstrated it.

If you choose to put forward a variant employing reactance, you could
at least step up to the bench to offer confirmatory or rejecting
evidence as I did. This is a simple example of offering a complete
analysis to peers for study and review. Some problems defy such
completeness, others defy analysis at the bench. This issue that I
have presented, and to which you toss in a variant are wholly germane
and within the capacity of any Ham to attempt to support or refute
through scientific method.

It is equally obvious that such methods and manners are an alien
concept competing with sneer review. As such, this disregard
constitutes the kulture of institutionalized ignorance that dominates
"debate."

Cecil, I seriously doubt your protestations of effusive gushing
I offered an experiment that might prove you right, Richard
in that of your crafted "might" (which certainly offers no prospect of
you actually performing any deed) is weighed with condescension. Such
passivity merely conforms to the existing kulture and hardly rises to
the effort and reportage I have already offered.

73's
Richard Clark, KB7QHC

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

Walt wrote -
Well, Reg, the reason I asked for an expression that includes the source
resistance in measuring SWR is that you said above that the internal
impedance
of the transmitter is ASSUMED to be 50 ohms. This implies that the SWR is
dependent on the internal impedance of the source, does it not ?

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

Walt, there's just a slight misunderstanding.


It is not I who makes that silly assumption - it is the stupid so-called
SWR + |rho| meter!


The meter indication is linearly proportional to |Rho|, from 0-to-1, from
zero to full-scale.


In effect, by means of its scale-calibration, it calculates SWR and Refl
power from |Rho|.


I understand conversion tables even appear in the handbooks.


The number 50-ohms appears in meter design calculations, and therefore
affects the meter indication of |Rho|.


One expression involved is |Rho| = (50-ZL)/(50+ZL) -


The meter therefore ASSUMES the impedance seen looking back towards the
transmitter from the meter is exactly 50 ohms.

But, as you well know, in the usual amateur situation, this assumption can
be, and often is, is wildly incorrect.


There are only a few remaining old-wives who still think it's true. But the
biased arguments still habitually remain.


As I have been saying for years, the solution is to change the name of the
undoubtably useful meter to TLI (Transmitter Loading Indicator). Forget
about SWR on an imaginary, non-existent transmission line and get into the
real world.


Don't shoot the messenger of apple-cart-upsetting news. It's not new to the
rigid old-wives Establishment.


Walt, please direct any criticism towards the education-disrupting meter
indications.


For design of so-called HF SWR meters download in a few seconds and run
immediately program SWRMETER from website below. Copious design notes are
included. I have just re-read them. After 3 years their readability could
be improved and updated but I have no intention of doing so.

-----------------------------------------------------
Walt sez,
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, you must have been familiar with the incorrect concept for years. As
we both know, changing the internal impedance of the transmitter cannot
possibly have any effect on SWR on the imaginary transmission line, if there
is one between transmitter and the meter. It is the meter itself which gives
silly answers because it, and its users, assumes a line of exactly 50-ohms,
longer than 1/2-wavelength actually exists. It doesn't!

----
=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================

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

Richard Clark wrote:

On Mon, 06 Oct 2003 15:16:04 -0500, Cecil Moore
wrote:

None of my statements has any meaning outside of the context in which
they are offered

Well, as this all thread started from one context:

everything can be explained by achieving a conjugate match

being so encompassing as to enlarge beyond your capacity to explain,
we find ourselves with shortfalls of example to any context.

But that's not what I said, Richard. Everything within the
original context can be explained by achieving a conjugate
match but you deleted the context and therefore misquoted me.

If I say, "It is always daylight at 12 noon." and you quote
me as saying "It is always daylight ", you have turned my true
statement into a false statement which is not an ethical thing
to do.
--
73, Cecil http://www.qsl.net/w5dxp



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David Robbins wrote:

"Cecil Moore" wrote:
Does (R+jXL)/(G+jXC) really equal 2500 for RG-174 on 12m? The specs
say the Z0 of RG-174 is a nominal 50 ohms.

of course its not exactly 2500, otherwise there would be no loss. but its
close, maybe 2500+j10 or something like that. and even the resistive part
may not be exact, the nominal 50 ohms could be 45 to 55 depending on the
tolerances of the manufacturer.

Comparing the 6dB loss of RG-174 to the 0.14 dB loss for hardline -
is all that extra loss accounted for in the +j10 term?
--
73, Cecil http://www.qsl.net/w5dxp



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On Tue, 7 Oct 2003 01:29:43 +0000 (UTC), "Reg Edwards"
wrote:

Walt wrote -
Well, Reg, the reason I asked for an expression that includes the source
resistance in measuring SWR is that you said above that the internal
impedance
of the transmitter is ASSUMED to be 50 ohms. This implies that the SWR is
dependent on the internal impedance of the source, does it not ?

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

Walt, there's just a slight misunderstanding.


It is not I who makes that silly assumption - it is the stupid so-called
SWR + |rho| meter!


The meter indication is linearly proportional to |Rho|, from 0-to-1, from
zero to full-scale.


In effect, by means of its scale-calibration, it calculates SWR and Refl
power from |Rho|.


I understand conversion tables even appear in the handbooks.


The number 50-ohms appears in meter design calculations, and therefore
affects the meter indication of |Rho|.


One expression involved is |Rho| = (50-ZL)/(50+ZL) -


The meter therefore ASSUMES the impedance seen looking back towards the
transmitter from the meter is exactly 50 ohms.

But, as you well know, in the usual amateur situation, this assumption can
be, and often is, is wildly incorrect.


There are only a few remaining old-wives who still think it's true. But the
biased arguments still habitually remain.


As I have been saying for years, the solution is to change the name of the
undoubtably useful meter to TLI (Transmitter Loading Indicator). Forget
about SWR on an imaginary, non-existent transmission line and get into the
real world.


Don't shoot the messenger of apple-cart-upsetting news. It's not new to the
rigid old-wives Establishment.


Walt, please direct any criticism towards the education-disrupting meter
indications.


For design of so-called HF SWR meters download in a few seconds and run
immediately program SWRMETER from website below. Copious design notes are
included. I have just re-read them. After 3 years their readability could
be improved and updated but I have no intention of doing so.

-----------------------------------------------------
Walt sez,
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, you must have been familiar with the incorrect concept for years. As
we both know, changing the internal impedance of the transmitter cannot
possibly have any effect on SWR on the imaginary transmission line, if there
is one between transmitter and the meter. It is the meter itself which gives
silly answers because it, and its users, assumes a line of exactly 50-ohms,
longer than 1/2-wavelength actually exists. It doesn't!

----
=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================

No Reg, I've never been familiar with the incorrect concept. I had never thought
anyone was that uninformed until you and Richard C brought it up here. I was
flabbergasted to think you held that position, so I'm relieved to know that you
aren't among the uninformed. And Richard's last two posts seemed
contradictory--I haven't yet totally understood what his position really is.

I'm sure you're aware that the voltage applied to the meter movement of the SWR
meter is actually making the indicator hand respond to the value of rho, but
with the scale graduated in units of SWR. To verify this we adjust the forward
reading for full scale for the reference reading. We then switch to the
reflected reading. Let's say the mismatch is 3:1 for rho = 0.5. If the SWR
indicator is accurate a voltmeter will now read 0.5. exactly half scale, where
the full-scale reading is 1.0.

Reg, I'm not lecturing you, because I know that you know this--this is my way of
telling you that I also know it.

Walt, W2DU