Gentlemen:
fFirst of all, stop bickering.
Second, you can't measure SWR. you can measure incident power (going to
the load) and reflected power power (coming back from the load). This
is done with a 20$ CB type power meter or with a 60 kilobucks network
analyzer, doesn't really matter!
You can CALCULATE the SWR using the formula. That, you can do!!!
what we call SWR meter s are actually directional couplers that employ
one form or another of phase and magnitude comparisons to separate
incident from reflected power and give a relative reading. The
measurement itself is meaningless without calibration and the coupler
operates in a ratiometric manner, i.e. the output is based on ratios of
signals, not their absolute value!
Alex 4Z5KS

"Saandy wrote

you can't measure SWR.
=========================================

I am pleased you agree with me.

=========================================
You can CALCULATE the SWR using the formula.
=========================================

But of what use is the SWR it after you have calculated it?

To what transmission line does it apply? Where is it? What are the
locations of max-volts and min-volts? It does NOT apply to the line
between transmitter and antenna. I suggest it exists only in your
imagination. ;o)

It is the name of "SWR Meter" which leads to confusion,
misunderstandings and arguments. The name says the instrument does
something which it does not do. With the help of old-wives, novices
are led astray and are stuck with incorrect ideas about standing-waves
for the rest of the lives.

Just change the name to TLI (Transmitter Loading Indicator) which is
what it is and does very well. The true meaning and associations of
SWR will then emerge and all will be flooded with the light of reason.
----
Reg, G4FGQ.

"Reg Edwards" wrote in message
...

"Saandy wrote

you can't measure SWR.
=========================================

I am pleased you agree with me.

=========================================
You can CALCULATE the SWR using the formula.
=========================================

But of what use is the SWR it after you have calculated it?

To what transmission line does it apply? Where is it? What are the
locations of max-volts and min-volts? It does NOT apply to the line
between transmitter and antenna. I suggest it exists only in your
imagination. ;o)

It is the name of "SWR Meter" which leads to confusion,
misunderstandings and arguments. The name says the instrument does
something which it does not do. With the help of old-wives, novices
are led astray and are stuck with incorrect ideas about standing-waves
for the rest of the lives.

Just change the name to TLI (Transmitter Loading Indicator) which is
what it is and does very well. The true meaning and associations of
SWR will then emerge and all will be flooded with the light of reason.
----
Reg, G4FGQ.

Hi Reg

I recognize that you know far more about VSWR and measuring complex load
impedances than I do.
I'm writing this to represent the "other side" of an arguement that states
that VSWR *cant* be measured. I claim that VSWR *can* be measured and that
VSWR can be used to identify the impedance terminating the transmission
line.

Jerry

Jerry Martes wrote:
I claim that VSWR *can* be measured and that
VSWR can be used to identify the impedance terminating the transmission
line.

The tuner SWR meter only indicates the SWR on the 50 ohm coax
between the transmitter and the tuner. However, I have an SWR
meter on the antenna side of my tuner and it does indeed indicate
the SWR on my transmission line.

XMTR--SWR meter#1--tuner--SWR meter#2--50 ohm coax to a G5RV

SWR meter#2 does indeed indicate the SWR on the coax feed to
my G5RV. It obviously does not indicate the SWR at the antenna.
--
73, Cecil http://www.qsl.net/w5dxp

"Cecil Moore" wrote
The tuner SWR meter only indicates the SWR on the 50 ohm coax
between the transmitter and the tuner. However, I have an SWR
meter on the antenna side of my tuner and it does indeed indicate
the SWR on my transmission line.

XMTR--SWR meter#1--tuner--SWR meter#2--50 ohm coax to a G5RV

SWR meter#2 does indeed indicate the SWR on the coax feed to
my G5RV. It obviously does not indicate the SWR at the antenna.
======================================

Cec, you are not telling the whole truth.

The meter tells you nothing about the important main G5RV transmission
line. ie., the SWR on the ladder line between the end of the coax and
the antenna. Neither can it tell you what the antenna input impedance
is.

There are other ways of finding the input impedance of the G5RV
antenna and its effect on line SWR if you should ever be sufficiently
interested. You could use a computer program. ;o)
----
Reg.

On Mon, 28 Nov 2005 17:54:35 GMT, "Jerry Martes"
wrote:


that VSWR *cant* be measured. I claim that VSWR *can* be measured and that
VSWR can be used to identify the impedance terminating the transmission
line.

Jerry, unless you redefine the term "impedance", you cannot generally
measure impedance with a typical reflectometer style SWR meter.

Impedance is a complex quantity (ie with real and imaginary parts).
There are an infinite number of different impedances (being
combinations of the real and imaginary parts) that could cause a given
SWR on a given line in most cases. (The exception is the case when
VSWR=1, you do know the impedance, it is the nominal Zo for which the
instrument was calibrated.)

Whilst you can work out the SWR that will result from a specific
impedance on a specific Zo line, you cannot do the inverse, you don't
have enough information.

Owen
--

Owen Duffy wrote:

wrote:
that VSWR *cant* be measured. I claim that VSWR *can* be measured and that
VSWR can be used to identify the impedance terminating the transmission
line.

Jerry, unless you redefine the term "impedance", you cannot generally
measure impedance with a typical reflectometer style SWR meter.

Here's how I do it, Owen. I modified my SWR meter to tell me
if the voltage sample is leading or lagging the current sample
and if the voltage sample is greater or less than the current
sample. Given the SWR is ratioed to 50 ohms, that's all I need.
I adjust the length of my feedline until I find a current maximum
point and the rest is easy.
--
73, Cecil http://www.qsl.net/w5dxp

"Jerry Martes" wrote
I'm writing this to represent the "other side" of an arguement
that states
that VSWR *cant* be measured. I claim that VSWR *can* be measured
and that
VSWR can be used to identify the impedance terminating the
transmission
line.
========================================

The only way to measure SWR on a transmission line is to run a
voltmeter along it. At least TWO measurements are needed. Not ONE.
And line length is involved.

The voltmeter readings will indeed tell you what the SWR is. But
nothing else. It will be possible to calculate from the readings and
the distance between max and min what the velocity of propagation is.

But it is essential to add extra critical information before anything
else can be deduced. Without this EXTRA information knowledge of the
SWR (if it can be obtained) is useless. The so-called SWR meter does
not and cannot provide this information.

To calculate the terminating impedances from the SWR it is neccsary
also to know the line impedance, its velocity and the exact locations
of the max-volts and min-volts relative to the ends. The meter will
not tell you.

And the foregoing is on a line which exists only in one's imagination.

I am sorry to repeat, the indications of the SWR meter apply only to
the input impedance of the line from the transmitter to the antenna.
The meter, in itself, tells you nothing about what is happening to
conditions along the line. It certainly tells you nothing about the
antenna's input impedance which is of primary interest.

IF, BY SOME MEANS, YOU CAN MEASURE SWR, then there is much more
information needed before the performance of the system can be
predicted.

The funny thing is - the performance of the system can be deduced
from the extra information without reference to the SWR. The whole
business is laughable.

Just change the name of the meter and all will become clear.
----
Reg, G4FGQ.

Reg Edwards wrote:
The only way to measure SWR on a transmission line is to run a
voltmeter along it.

Reg, what about Rho = SQRT(P-/P+) and SWR=(1+Rho)/(1-Rho)?
--
73, Cecil http://www.qsl.net/w5dxp

"Reg Edwards" wrote in message
...

"Jerry Martes" wrote
I'm writing this to represent the "other side" of an arguement
that states
that VSWR *cant* be measured. I claim that VSWR *can* be measured
and that
VSWR can be used to identify the impedance terminating the
transmission
line.
========================================

The only way to measure SWR on a transmission line is to run a
voltmeter along it. At least TWO measurements are needed. Not ONE.
And line length is involved.

The voltmeter readings will indeed tell you what the SWR is. But
nothing else. It will be possible to calculate from the readings and
the distance between max and min what the velocity of propagation is.

But it is essential to add extra critical information before anything
else can be deduced. Without this EXTRA information knowledge of the
SWR (if it can be obtained) is useless. The so-called SWR meter does
not and cannot provide this information.

To calculate the terminating impedances from the SWR it is neccsary
also to know the line impedance, its velocity and the exact locations
of the max-volts and min-volts relative to the ends. The meter will
not tell you.

And the foregoing is on a line which exists only in one's imagination.

I am sorry to repeat, the indications of the SWR meter apply only to
the input impedance of the line from the transmitter to the antenna.
The meter, in itself, tells you nothing about what is happening to
conditions along the line. It certainly tells you nothing about the
antenna's input impedance which is of primary interest.

IF, BY SOME MEANS, YOU CAN MEASURE SWR, then there is much more
information needed before the performance of the system can be
predicted.

The funny thing is - the performance of the system can be deduced
from the extra information without reference to the SWR. The whole
business is laughable.

Just change the name of the meter and all will become clear.
----
Reg, G4FGQ.

Hi Reg

I have no understanding of why you find it important to state things that
are not true about VSWR. VSWR *can* be measured. It is clear to me that
you know that the Complex Impedance terminating a transmission line can
determined by measuring the VSWR. Sure, it requires the position of the
voltage mins (or maxs) be identified, with the load and then with a short
ckt., and a Smith chart to be used for quick/easy identification of the load
impedance. But, is that so much calculation that you find it necessary to
state " IF, BY SOME MEANS, YOU CAN MEASURE SWR, then there is much more
information needed before the performance of the system can be
predicted".

The load impedance isnt "predicted". It is actually *determined* with an
accuracy associated with the precision of the test equipment.

I consider measuring VSWR on a transmission line to be an excellent method
of determining load impedance.

Jerry

Jerry