SWR again.
 

******* Copied from uk.radio.amateur newsgroup. ********

Reg spoke of the SWR meter as a resistance bridge. It is possible to
build a
meter that is a bridge
===================================

The so-called SWR meter is ALWAYS a resistance bridge (although it may
be described in other terms).

In the HF, 100 watt models, the little ferrite ring is a current
transformer. The turns ratio on the transformer allows the bridge
resistors to be changed to values other than 50-ohms.

For example a bridge resistor which is across the transmitter changes
to 5000 ohms. And a bridge resistor in series with the load changes
to 0.5 ohms. In both cases the power lost in the resistors falls to
the order of 1% of the power which would be lost in 50 ohm resistors.

The meter becomes far more power efficient. With 50-ohm bridge ratio
arms the power lost in the bridge would be 75 percent of Tx power
output.

The 0.5-ohm resistor does not exist. Very cleverly, the input
resistance of the one turn primary winding on the current transformer
becomes the 0.5-ohm bridge arm.

The DC seperation between primary and secondary windings on the
current transformer allows the diode rectifier and moving coil DC
microameter circuit to be operated very nicely all at ground
potential.
----
Reg, G4FGQ

The term 'meter' is incorrect. It does not 'measure' anything. It
merely 'indicates'.

SWR again.
 

Reg,
You said,"The term 'meter' is incorrect. It does not 'measure'
anything. It merely 'indicates'." ... Sounds a lot like a definition
of a politician. What comes out is what was fed in, with about
10% accuracy...
'Doc

SWR again.
 

You said,"The term 'meter' is incorrect. It does not 'measure'
anything. It merely 'indicates'." ... Sounds a lot like a definition
of a politician. What comes out is what was fed in, with about
10% accuracy...
'Doc

Same over here except that it's only 5%. I have more faith in SWR
meters with bent needles.
---
Reg.

SWR again.
 

Reg Edwards wrote:

You said,"The term 'meter' is incorrect. It does not 'measure'
anything. It merely 'indicates'." ... Sounds a lot like a definition
of a politician. What comes out is what was fed in, with about
10% accuracy...
'Doc


Same over here except that it's only 5%. I have more faith in SWR
meters with bent needles.


A man with a watch knows the time.

A man with two watches is never sure......



- Mike KB3EIA -

SWR again.
 

This is getting a bit far from antennas, but the way to know the uncertainty
in knowing time is to have multiple clocks. NBS (whatever it now calls
itself) has a bunch of clocks that are compared to each other.
When I was young (and WWV was back East) the uncertainty indicated from
multiple clocks was a few parts in ten to the eighth power. Today, that
uncertainty is a few parts in ten to the 13th power! It takes multiple
clocks to know the uncertainty.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Michael Coslo" wrote in message
...

snip


A man with a watch knows the time.

A man with two watches is never sure......



- Mike KB3EIA -

SWR again.
 

Even a broken clock is quite accurate, TWICE a day (the 12 hour
variety)! Jim NN7K

J. Mc Laughlin wrote:
This is getting a bit far from antennas, but the way to know the uncertainty
in knowing time is to have multiple clocks. NBS (whatever it now calls
itself) has a bunch of clocks that are compared to each other.
When I was young (and WWV was back East) the uncertainty indicated from
multiple clocks was a few parts in ten to the eighth power. Today, that
uncertainty is a few parts in ten to the 13th power! It takes multiple
clocks to know the uncertainty.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Michael Coslo" wrote in message
...

snip


A man with a watch knows the time.

A man with two watches is never sure......



- Mike KB3EIA -

SWR again.
 

Reg Edwards wrote:
******* Copied from uk.radio.amateur newsgroup. ********

Reg spoke of the SWR meter as a resistance bridge. It is possible to
build a
meter that is a bridge
===================================

The so-called SWR meter is ALWAYS a resistance bridge (although it may
be described in other terms).

Utter nonsense.

There are numerous ways to measure SWR without using a bridge of any
kind.

A bridge implementation is mearly a simple and cheap way to do it and
hence the most likely to be found in use by a hobbiest.

snip remainder

--
Jim Pennino

Remove .spam.sux to reply.

SWR again.
 

Reg spoke of the SWR meter as a resistance bridge. It is
possible to
build a
meter that is a bridge
===================================

The so-called SWR meter is ALWAYS a resistance bridge (although it
may
be described in other terms).

Utter nonsense.

There are numerous ways to measure SWR without using a bridge of any
kind.

A bridge implementation is mearly a simple and cheap way to do it
and
hence the most likely to be found in use by a hobbiest.

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

I'm sorry to say you are all banging your heads against a brick wall.

The so-called SWR meter does NOT measure SWR.

For starters, there is no transmission line on which to measure
anything. Can you find one? It is NOT the one which goes between
tuner and antenna.

To measure SWR on THAT line the meter has to be located in the air at
the antenna end of the line and has to be read using an astronomical
telescope mounted on a tripod. But it would still give the wrong
answers.

Go and think about it some more.
----
Reg, G4FGQ

SWR again.
 

Reg Edwards wrote:
Reg spoke of the SWR meter as a resistance bridge. It is
possible to
build a
meter that is a bridge
===================================

The so-called SWR meter is ALWAYS a resistance bridge (although it
may
be described in other terms).

Utter nonsense.

There are numerous ways to measure SWR without using a bridge of any
kind.

A bridge implementation is mearly a simple and cheap way to do it
and
hence the most likely to be found in use by a hobbiest.

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

I'm sorry to say you are all banging your heads against a brick wall.

It feels that way when trying to discuss SWR with you.

The so-called SWR meter does NOT measure SWR.

Depends on what you call a SWR meter and what you mean by measure,
but this has already been hashed to bits.

For starters, there is no transmission line on which to measure
anything. Can you find one? It is NOT the one which goes between
tuner and antenna.

It depends on how you implement the hardware to measure SWR, but you
are so obsessed with bridge circuits you have little chance of
understanding there is more in the world.

What do tuners have to do with anything? Tuners are irrelevant to
the original post. Are you deliberately trying to confuse the issue
or do tuners confuse you?

To measure SWR on THAT line the meter has to be located in the air at
the antenna end of the line and has to be read using an astronomical
telescope mounted on a tripod. But it would still give the wrong
answers.

Go and think about it some more.

I did in EE class about 30 years ago and numerous times since. Guess
what, the physics hasn't changed.

You are so obsessed on this issue that the small nugget of information
you have to offer is swamped by the enormous amount of arm waving
and babble.

----
Reg, G4FGQ



--
Jim Pennino

Remove .spam.sux to reply.

SWR again.
 

You are so obsessed on this issue that the small nugget of
information
you have to offer is swamped by the enormous amount of arm waving
and babble.

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

I'm afraid your reduction to personalities is a positive indication to
bystanders you have lost the argument and have accepted defeat.

No hard feelings! Have a good day!
----
Reg, G4FGQ

SWR again.
 

"Tom Ring" wrote
As someone who has watched from the sidelines for quite a while, I
think
you need to consult a psychiatrist, You really are obsessed over
this.
I am not kidding, no ****.

You seem normal in most of your responses, but when it comes to SWR
meters you really do seem to lose it.
----------------------------------------------------------------------
-----

Doctor Tom,

Hasn't it occurred to you that if most of my responses are normal then
there's no reason to suppose my response to so- called SWR meters
should be otherwise.

If ever I should feel the need to consult a psychiatrist then I would
make arrangements to see one. I would ignore the unqualified opinions
of quacks and old-wives on this newsgroup who have allowed themselves
to be brainwashed just by the mis-naming of an indicating instrument.

My only reason for continuing with the subject is to provide some
education to novices although it seems some of the 'experts' are also
in need of it.

If YOU wish to continue with the subject then please say which of my
very few earlier technical statements you think are incorrect, and why
you think so.

If the discussion should drift towards my personal character then it
will be taken as an indication you have lost the argument and have
nothing further to say.

Otherwise go QRT
----
Reg, G4FGQ

SWR again.
 

I wonder how many band openings both of you have missed while participating
in this cyber ****ing contest?

--

Charlie


"Reg Edwards" wrote in message
...

"Tom Ring" wrote
As someone who has watched from the sidelines for quite a while, I
think
you need to consult a psychiatrist, You really are obsessed over
this.
I am not kidding, no ****.

You seem normal in most of your responses, but when it comes to SWR
meters you really do seem to lose it.
----------------------------------------------------------------------
-----

Doctor Tom,

Hasn't it occurred to you that if most of my responses are normal then
there's no reason to suppose my response to so- called SWR meters
should be otherwise.

If ever I should feel the need to consult a psychiatrist then I would
make arrangements to see one. I would ignore the unqualified opinions
of quacks and old-wives on this newsgroup who have allowed themselves
to be brainwashed just by the mis-naming of an indicating instrument.

My only reason for continuing with the subject is to provide some
education to novices although it seems some of the 'experts' are also
in need of it.

If YOU wish to continue with the subject then please say which of my
very few earlier technical statements you think are incorrect, and why
you think so.

If the discussion should drift towards my personal character then it
will be taken as an indication you have lost the argument and have
nothing further to say.

Otherwise go QRT
----
Reg, G4FGQ

SWR again.
 

Charlie wrote:

I wonder how many band openings both of you have missed while participating
in this cyber ****ing contest?


Let's see, I have made one comment on the subject of Reg and SWR
measurement. Ever.

So probably none.

And all I said was that he seemed to be obsessive. I never said
anything about the validity of his arguments, so I cerainly was not
involved in a ****ing contest.

I think it's all quite amusing actually.

tom
K0TAR

SWR again.
 

I think it's all quite amusing actually.

tom
K0TAR
===================================

So do I.
----
Reg, G4FGQ

SWR again.
 

Reg Edwards wrote:
I think it's all quite amusing actually.

tom
K0TAR

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

So do I.
----
Reg, G4FGQ



It ceased to be amusing 500 posts ago, but Reg has
a point, however strained.
73,
Tom Donaly, KA6RUH

SWR again.
 

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

SWR again.
 

"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.

SWR again.
 

"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

SWR again.
 

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

SWR again.
 

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
--

SWR again.
 

"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.

SWR again.
 

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

SWR again.
 

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

SWR again.
 

"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.

SWR again.
 

On Mon, 28 Nov 2005 20:45:37 GMT, Cecil Moore wrote:

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.

Nice try Cecil.

Note Jerry's statement: "VSWR can be used to identify the impedance
terminating the transmission line".

Your method, impractical as it is, means you have found a point where
the impedance at the instrument terminals is purely resistive, and a
minimum, and you are correct that you could calculate the value of
that resistance. That measurement does not tell you the "impedance
terminating the transmission line" unless the line is of zero length.
You could make another measurement with another instrument (line
length using a ruler) and using other knowledge, calculate the
"impedance terminating the transmission line".

In a practical situation, there is a risk that there is current
flowing on the outer of a coaxial line or unbalance current in the
case of an open wire line. In that case, changing the feedline length
may affect the load impedance at the end of the line, so your proposed
method may alter the very thing you are "measuring".

Knowledge of the SWR AND the position of the standing wave pattern wrt
the load AND the loss characteristics of the line is enough
information to determine the "impedance terminating the transmission
line"... but a typical reflectometer SWR meter does not measure all of
those things.

Owen
--

SWR again.
 

Cecil Moore wrote:
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)?


If you know the forward and reflected power, VSWR can be calculated as
follows:

VSWR=(1+sqrt Pr/Pi) / (1-sqrt Pr/Pi)

I believe.

--
Over The Hill
__________________________________________________ ___________________________

The question of whether computers can think is like the question of
whether submarines can swim.

***Edsgar Dijkstra***

SWR again.
 

Reg, what about Rho = SQRT(P-/P+) and SWR=(1+Rho)/(1-Rho)?
==================================
Cec, That's a calculation, merely arithmetic, not a measurement.

It applies only to a long line lossless line which does not exist but
Zo must be 50 ohms. And nobody has the foggiest idea where max-volts
and min-volts are located. And so the calculated information is
useless except for trolling on newsgroups. ;o)
----
Reg.

SWR again.
 

Reg Edwards wrote:
Reg, what about Rho = SQRT(P-/P+) and SWR=(1+Rho)/(1-Rho)?

==================================
Cec, That's a calculation, merely arithmetic, not a measurement.

It applies only to a long line lossless line which does not exist but
Zo must be 50 ohms. And nobody has the foggiest idea where max-volts
and min-volts are located. And so the calculated information is
useless except for trolling on newsgroups. ;o)
----
Reg.


Here are several VSWR measurement techniques. They are real they are
valid and I used them for years. VSWR is a *very* important parameter,
especially when dealing with high power systems.

http://people.deas.harvard.edu/~jone...ssign_3_98.pdf

--
Over The Hill
__________________________________________________ ___________________________

The question of whether computers can think is like the question of
whether submarines can swim.

***Edsgar Dijkstra***

SWR again.
 

Reg Edwards wrote:
Reg, what about Rho = SQRT(P-/P+) and SWR=(1+Rho)/(1-Rho)?
==================================
Cec, That's a calculation, merely arithmetic, not a measurement.

It applies only to a long line lossless line which does not exist but
Zo must be 50 ohms. And nobody has the foggiest idea where max-volts
and min-volts are located. And so the calculated information is
useless except for trolling on newsgroups. ;o)
----
Reg.
Hi Reg, Do you advocate changing the measurement and calaculation that
all our handy little Antenna Analyzers report as SWR to TLI? That
would cost a lot to re-tool. My MFJ-259, and I think you have stated
that you have one also, reports lots of useful info, and uses a bridge,
a PIC, and a neat display. SWR as well as many other parameters are
measured indirectly, and calculated with the Micro. You could make the
agrument that all the other stuff the Analyzer reports needs to be more
descriptive, but it would cost too much to change. If you read the
manual, and know what the displays on any meter really means, then why
change anything?
Gary N4AST

SWR again.
 

Owen Duffy wrote:
Your method, impractical as it is, ...

"My method" was in widespread use before I was born. I learned
it from my Elmer in the early 50's. He was always looking for
that "magic" current maximum point to feed from his link
coupled tank circuit.

... means you have found a point where
the impedance at the instrument terminals is purely resistive, and a
minimum, and you are correct that you could calculate the value of
that resistance. That measurement does not tell you the "impedance
terminating the transmission line" unless the line is of zero length.

A transmission line transforms the impedance in a predictable
manner given the transmission line specifications. One can
backtrack the SWR spiral on a Smith Chart to get a reasonable
estimate for the antenna impedance. The impedances for my dipole
calculated in such a manner are pretty close to the ones predicted
by EZNEC.

In that case, changing the feedline length
may affect the load impedance at the end of the line, ...

The load impedance is what it is, virtually unaffected by
feedline length.

... so your proposed
method may alter the very thing you are "measuring".

Virtually every time one makes a measurement, one alters the
very thing that one is measuring. That's just a fact of life
and not a valid reason to give up trying to make measurements.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

Reg Edwards wrote:

Reg, what about Rho = SQRT(P-/P+) and SWR=(1+Rho)/(1-Rho)?

It applies only to a long line lossless line which does not exist but
Zo must be 50 ohms.

Let's say we have the following system configuration with
a 1:1 choke at '+':

100W XMTR---50 ohm coax---+---300 ohm twinlead---...
Pfor1=100w-- Pfor2--
--Pref1=0w --Pref2

What's the forward power on the 300 ohm twinlead?
What's the reflected power on the 300 ohm twinlead?
What's the SWR on the 300 ohm twinlead?
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

"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

SWR again.
 

On Mon, 28 Nov 2005 23:52:40 GMT, Cecil Moore wrote:

Owen Duffy wrote:

that resistance. That measurement does not tell you the "impedance
terminating the transmission line" unless the line is of zero length.

A transmission line transforms the impedance in a predictable
manner given the transmission line specifications. One can
backtrack the SWR spiral on a Smith Chart to get a reasonable
estimate for the antenna impedance. The impedances for my dipole

To do that, you need to determine the position of the standing wave
pattern with respect to the load, and a typical reflectometer style
SWR meter does not do that. You could put a ruler to the line, but you
are using another instrument to make a another measurement that the
reflectometer could not make.

It is misleading to suggest that a reflectometer style SWR meter alone
is useful for determining the impede dance of a load connected to the
meter by a length of transmission line, save possibly the case when
VSWR=1 and the line is low loss and Zo is the same as the calibration
Z of the SWR meter.

Owen
--

SWR again.
 

Owen Duffy wrote:
To do that, you need to determine the position of the standing wave
pattern with respect to the load, and a typical reflectometer style
SWR meter does not do that.

Yes it does, if one has the ability to vary the length of the feedline
until a current maximum point (minimum SWR) is known to be located at
the balun/choke. I do it everytime I get on the air. That's how I tune
my antenna system and I don't use any conventional tuner at all.

It is misleading to suggest that a reflectometer style SWR meter alone
is useful for determining the impedance of a load connected to the
meter by a length of transmission line, save possibly the case when
VSWR=1 and the line is low loss and Zo is the same as the calibration
Z of the SWR meter.

Not misleading at all. I do it all the time. I know the exact length,
velocity factor, and Z0 of my feedline. I know an SWR current maximum
point is located at my choke. I know if it is greater than, less than,
or equal to 50 ohms. It is a rather simple-minded process to accurately
estimate the antenna feedpoint impedance given everything I know. You
should try it sometime. Even if I didn't know if the current maximum
impedance was lower than or higher than 50 ohms, there would only be
two possible antenna impedances. EZNEC has a perfect track record in
predicting which of those two antenna impedances actually exists.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

Have it your way Cecil...

Owen
--

SWR again.
 

Cecil, there's no need to rack your brains for hours trying to deduce
the antenna input impedance from the input impedance of the
transmission line. There's a computer program which will tell you the
exact answer in milliseconds. Download program ZL_Zin from website
below.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

SWR again.
 

Cec,

The meter indicates SWR on the 50-ohm coax between meter and
transmitter. It HAS to be 50-ohm coax. Any other impedance and you
get the wrong answer. Without measurement of Zo = 50 ohms it can only
be assumed.

You then include in the calculation the measurement or assumption of
the Zo of the 50-ohm coax, and the measurement or assumption of Zo of
the twin-line, and the forward and reverse powers, and the SWR on the
twin line can be deduced or assumed.

But if you think you are measuring SWR on anything you are cheating
and fooling yourself.

In your particular case an assumptiom of Zo = 450 ohms for the
twinline would be very much in error because both you and I know you
have measured Zo to be 380 ohms. I can tell you what the SWR is on
YOUR feedline without getting out of this armchair. I don't need to
know your meter readings. ;o)
----
Reg.

SWR again.
 

"Jerry Martes" wrote
I have no understanding of why you find it important to state things
that
are not true about VSWR.

===================================
Jerry,

It is important because the SWR meter is EDUCATIONAL. It is more than
a pair of red and green LED's on our automatic tuners.

All along I have stated that the name of the so-called SWR meter
should be changed. Other more technical statements have been made to
convince they whose state of mind prevents agreement.

Remarkably few people disagree with my technical statements but offer
no reasons for disagreement or prove me to be incorrect.

SWR meters are by far the most prevelent topic on amateur radio
newsgroups. It appears time and time again in contexts which
demonstrate it to be a source of misunderstandings, arguments and
general confusion.

I maintain that the instrument's name is the root cause of the
problems. It does not do what its name says it does. This inevitably
leads people, not just novices and CB-ers, into incorrect channels of
thought which become deeply ingrained. It unnecessarily introduces
SWR into discussions which actually have nothing to do with SWR. And
worst of all, when operating equipment, it causes people to have
problems which either don't exist or are different to what people
imagine they are. Mis-education is the keyword.

Re-naming should begin in amateur radio handbooks and similar
publications. Editors should be the first to be educated.

SWR meters are seldom mentioned as such in professional text books.
They are given other more correct names. Terman manages very well
wthout them. But there's nothing wrong with his bibles. (Yes, I know
they probably hadn't been invented in his day.)

Perhaps when our Chinese friends enter the amateur radio market,
manufacturers' wisdom will allow the light of reason to shine through.
But they will have to get a move on. I can foresee the time when
automatic tuners are universal and the only meter on black boxes will
be the S-meter.

I don't doubt that you thoroughly understand how the so-called SWR
meter works. But even the present discussion is enough to demonstrate
that a simple change is needed. In the end it all reduces to
economics and survival of the fittest argument.
----
Reg, G4FGQ

SWR again.
 

Gerry,

The load is the antenna - about which the SWR meter knows absolutely
nothing. All the the meter has to work with is the input impedance of
the tuner or the transmission line.

Line input Z = R+jX and to aggravate matters the meter discards all
information about X.
----
Reg.

SWR again.
 

Cecil, I note you have changed the name from "SWR Meter" to "Forward &
Reverse Power Meter", a procedure I have been recommending for years.
Congratulations!

Although I am not altogether happy with your choice of new name.
----
Reg.