On Tue, 27 Sep 2005 15:21:51 +0000 (UTC),
wrote:

Owen Duffy wrote:
On Tue, 27 Sep 2005 02:54:31 +0000 (UTC),
wrote:

Owen Duffy wrote:
On Tue, 27 Sep 2005 02:25:11 +0000 (UTC),
wrote:


SWR is nothing more than a dimensionless impedance ratio.

The fundamental definition of SWR flows from the behaviour and
properties of RF transmission lines.

And power=EI. And it also equals I^2*R and E^2/R.

SWR can be expressed in terms of power ratios, current ratios, and
impedance ratios.

When a transmission line is terminated in an impedance other than its
characteristic impedance, there will be both a forward wave and a
reflected wave of such magnitude to resolve the conditions that must
apply at the termination.

Irrelevant.

The forward wave and the reflected wave sum at all points along the
line having regard for their magnitudes and relative phase to produce
a "standing wave". The Standing Wave Ratio (SWR or VSWR) is defined to
mean the ratio of the maximum to the minimum of the magnitude of the
standing wave voltage pattern along the line.

Is is also defined as a current ratio and an impedance ration.

The SWR on a lossless line can be calculated knowing the complex
characteristic impedance of the line and the complex load impedance.

What no waves, just impedences!! Now you are contidicting yourself.

The SWR on the line does not depend in any way on some unrelated
independent reference resistance as you suggest in your formula.

Read it again.

The R is the R of the thing at the end of the line.

The X is the X of the thing at the end of the line.

The X is the impedance of the line.

You seem to be suggesting that your redefined SWR is a really good
(obscure) way to talk about an impedance (independently of a
transmission line) in terms of some standardised reference value, and
you can throw away the fundamental meaning of SWR to support your
SWR(50) concept. In your terms (independently of a transmission line),
for instance, a Z of 60+j10 would be SWR(50)=1.299, and so would an
infinite number of other Zs have SWR(50)=1.299... how is that of
value. To know Z is 60+j10 is to know more than to know SWR(50)=1.299.

The equations given are general and can be derived from first priciples.

The Z in the equations is the Z of your reference, i.e. 50 for a 50
Ohm system.

SWR is *ALWAYS* relative to some reference impedance.


Jim, your comments are full of inconsistencies (like pronumeral X
having two different meanings in the same formula, equations described
as "general" but which do not allow for a reactance component in your
"reference z" which is actually the characteristic impedance of the
line in the real world, equations derived from first principles and
you state the first principles are "irelevant").

In the absence of logic in your writing, I won't waste anymore time...
you have some deeply entrenched misconceptions and seem to have built
a large framework of simple views (like power=EI... a DC circuits
concept) to support the misconceptions.

Owen
--

Reg Edwards wrote:
Cec, you can make the meter read anything you like just by twiddling
the calibration pot. Of what bloody use is that? !**?!!

Just answer the obvious question. No If's or But's

I did answer the question, Reg. You just didn't like the
answer.

Let's say we have an SWR meter at point 'x' in the following
diagram:

XMTR---1WL 50 ohm coax---x---1WL 75 ohm coax---100 ohm load

If the meter is calibrated for 50 ohms, it will indicate the
SWR on the 50 ohm coax, 2:1, on the source side of the meter.

If the meter is calibrated for 75 ohms, it will indicate the
SWR on the 75 ohm coax, 1.33:1, on the load side of the meter.

An SWR meter samples the magnitude and phase of the voltage,
samples the magnitude and phase of the current, assumes
it exists in the Z0 environment for which it was calibrated,
and accurately reports those results.

If the SWR meter is installed in a Z0 environment other than
that for which it was calibrated, the instrument is being
misused and the operator is at fault, not the instrument.
Any instrument can be misused.
--
73, Cecil http://www.qsl.net/w5dxp

Owen Duffy wrote:
On Tue, 27 Sep 2005 15:21:51 +0000 (UTC),
wrote:

Owen Duffy wrote:
On Tue, 27 Sep 2005 02:54:31 +0000 (UTC),
wrote:

Owen Duffy wrote:
On Tue, 27 Sep 2005 02:25:11 +0000 (UTC),
wrote:


SWR is nothing more than a dimensionless impedance ratio.

The fundamental definition of SWR flows from the behaviour and
properties of RF transmission lines.

And power=EI. And it also equals I^2*R and E^2/R.

SWR can be expressed in terms of power ratios, current ratios, and
impedance ratios.

When a transmission line is terminated in an impedance other than its
characteristic impedance, there will be both a forward wave and a
reflected wave of such magnitude to resolve the conditions that must
apply at the termination.

Irrelevant.

The forward wave and the reflected wave sum at all points along the
line having regard for their magnitudes and relative phase to produce
a "standing wave". The Standing Wave Ratio (SWR or VSWR) is defined to
mean the ratio of the maximum to the minimum of the magnitude of the
standing wave voltage pattern along the line.

Is is also defined as a current ratio and an impedance ration.

The SWR on a lossless line can be calculated knowing the complex
characteristic impedance of the line and the complex load impedance.

What no waves, just impedences!! Now you are contidicting yourself.

The SWR on the line does not depend in any way on some unrelated
independent reference resistance as you suggest in your formula.

Read it again.

The R is the R of the thing at the end of the line.

The X is the X of the thing at the end of the line.

The X is the impedance of the line.

You seem to be suggesting that your redefined SWR is a really good
(obscure) way to talk about an impedance (independently of a
transmission line) in terms of some standardised reference value, and
you can throw away the fundamental meaning of SWR to support your
SWR(50) concept. In your terms (independently of a transmission line),
for instance, a Z of 60+j10 would be SWR(50)=1.299, and so would an
infinite number of other Zs have SWR(50)=1.299... how is that of
value. To know Z is 60+j10 is to know more than to know SWR(50)=1.299.

The equations given are general and can be derived from first priciples.

The Z in the equations is the Z of your reference, i.e. 50 for a 50
Ohm system.

SWR is *ALWAYS* relative to some reference impedance.


Jim, your comments are full of inconsistencies (like pronumeral X
having two different meanings in the same formula, equations described
as "general" but which do not allow for a reactance component in your
"reference z" which is actually the characteristic impedance of the
line in the real world, equations derived from first principles and
you state the first principles are "irelevant").

The last line is obviously a typo, it should be:

The Z is the impedance of the line.

Z is an impedance. An impedance is an absolute value.

The impedance of RG-8 coax, for example, is approximately 50 Ohms.

As I said, if you don't believe the equations, go get some resistors
and capacitors and do an experiment.

Until you do that you have no case.

In the absence of logic in your writing, I won't waste anymore time...
you have some deeply entrenched misconceptions and seem to have built
a large framework of simple views (like power=EI... a DC circuits
concept) to support the misconceptions.

Sigh, the power thing was a simple illustration of the fact that a
thing can often be represented a number of different ways.

How about acceleration is the first derivative of velocity and also
the second derivative of position? Do you like this example better?

Owen
--

--
Jim Pennino

Remove .spam.sux to reply.

Richard Harrison wrote:
You drive an automobile and glance at the speedometer. It is an
electrical meter giving an indication proportional to vehicle speed.

And if you think it is calibrated in km/hour when it is
actually calibrated in miles/hour, your speed reading will
be in error and you may get a ticket. This is akin to an
SWR meter being calibrated for the wrong Z0.
--
73, Cecil http://www.qsl.net/w5dxp

There is no mystery about the 'required additional information'.

The nearest the so-called SWR meter ever gets to measuring anything is
the "magnitude of the reflection coefficient", MRC, which arises due
to the impedance of whatever is presented to the meter's output
terminals. (Recall, this impedance is the 4th variable arm of the
meter's RF resistance bridge.)

This impedance can have an angle anywhere between 90 and -90 degrees.
And the MRC can have an angle in any of the 4 quadrants, ie., anywhere
between 0 and 360 degrees.

But the meter is capable of indicating ONLY the MRC. All the angle
information is lost and gone forever. This is equivalent to losing
information about the location along the line of the peaks and troughs
in the standing wave. That is, of course, if a long line extending
back from the input of the meter to the transmitter actually exists.

Now, if the line with standing wave exists, the magnitude of the SWR
can be calculated from -

SWR = (1 + MRC) / (1 - MRC)

or the meter scale can be calibrated in terms of SWR.

It is frequently thought the SWR can be used to calculate the power
lost in the line. But, particularly when the the line is less than
1/4-wavelength long, this is not so. It requires the location of peaks
and troughs to be known - which they are not.

It is also thought that by rearranging the equation it is possible to
calculate the reflection coefficient from the indicated SWR. Wrong
again - can't be done, and in any case the reflection coefficient is
useless without an angle.

So the indicated SWR is not of much use except to provide a topic of
conversation. On the other hand, just by recalibrating the meter
scale, you can have a valuable, indispensible TLI.

By the way, I hear Californian wine makers have been hijacking the
names of French grape-growing districts and have been obliged to
re-calibrate their bottles. Ah well, back to the Chilian stuff.
----
Reg.

On Wed, 28 Sep 2005 04:07:21 +0000 (UTC), "Reg Edwards"
wrote:

There is no mystery about the 'required additional information'.

Hi Reg,

Of course, no one thought so except you - until now, and you still
have nothing to offer that distinguishes the probe method from the
common SWR meter available to every CB operator.

By the way, I hear Californian wine makers have been hijacking the
names of French grape-growing districts

Boy, are you late in taking in your newspaper. This has been going on
since the American vineyards saved the French lines from a devastating
rust blight decades ago. There is no original French line that has
not been re-planted from American root cuttings for half a century or
more after the Germans tilled their soil with Stukas.

73's
Richard Clark, KB7QHC

Reg Edwards wrote:
It is frequently thought the SWR can be used to calculate the power
lost in the line. But, particularly when the the line is less than
1/4-wavelength long, this is not so. It requires the location of peaks
and troughs to be known - which they are not.

In my no-tuner system of tuning, the peaks and troughs are known.
The purely resistive current maximum point is always located at
the balun/choke.
--
73, Cecil http://www.qsl.net/w5dxp

Richard Clark wrote:
Boy, are you late in taking in your newspaper. This has been going on
since the American vineyards saved the French lines from a devastating
rust blight decades ago. There is no original French line that has
not been re-planted from American root cuttings for half a century or
more after the Germans tilled their soil with Stukas.

A lot of those American wine-making families had French roots. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Reg, I think you're tilting at windmills.

=======================================
Dave,

First I am called Punchinello, and now Don Quixote is implied.

Yet you have repeatedly said "Reg is correct".

The only thing I have ever asked is to change the NAME.

It is the NAME itself which causes ill-educated IEEE members and
befuddled university professors to become old wives. They are reduced
to CB-ers who perhaps can be forgiven for being fooled just by a NAME.
They actually believe the thing measures SWR on a line which does not
exist. Or they find a line which does exist but on which it is
impossible for the thing to measure anything because it is located in
the wrong place. Their contorted imaginations somehow allow them to
argue interminably between themselves but without ever coming to
sensible conclusions on which they can agree. The evidence of battles
about waves, reflections, re-reflections, virtual reflections,
conjugate matches, etc, etc, is littered around these newsgroups. And
it's all due to a misnomer.

Just change the name of the so-called SWR meter and 50 years of bitter
warfare will revert once again to blessed peace and an understanding
of how things really work. Sack your lawyers.

And if anybody should think I take all this seriously then think
again. ;o)
----
Reg, G4FGQ

Reg Edwards wrote:
Or they find a line which does exist but on which it is
impossible for the thing to measure anything because it is located in
the wrong place.

Reg, the SWR meter may be smarter than you think. Here's
an experiment for you. The system is lossless.

XMTR--a--1WL 50 ohm--b--1WL 75 ohm--c--1WL 92 ohm--d--load

An SWR meter calibrated for 50 ohms will read the SWR on
the 50 ohm feedline when installed at points a,b,c, or d.

An SWR meter calibrated for 75 ohms will read the SWR on
the 75 ohm feedline when installed at points a,b,c, or d.

An SWR meter calibrated for 92 ohms will read the SWR on
the 92 ohm feedline when installed at points a,b,c, or d.

Now Reg, you have to admit that an SWR meter that can read
the SWR on the 92 ohm feedline when installed at point 'a'
is a darned smart meter. :-)
--
73, Cecil, http://www.qsl.net/w5dxp