John S wrote:
On 7/9/2015 12:40 PM, wrote:
Jeff wrote:
On 08/07/2015 19:14, wrote:
John S wrote:
On 7/7/2015 1:44 PM, wrote:
Ian Jackson wrote:
In message , Jerry Stuckle
writes


Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there.

If there's no reflection, there can be no standing wave. So, being
pedantic, there's no such thing as an SWR of 1:1!

Despite the name, VSWR is defined in terms of complex impedances
and wavelengths, not "waves" of any kind.



Actually, VSWR is defined as the ratio of Vmax/Vmin.

Actually, VSWR can be defined several ways, one of which is:

(1 + |r|)/(1 - |r|)

Where r is the reflection coefficient which can be defined a:

(Zl - Zo)/(Zl + Zo)

Where Zl is the complex load impedance and Zo is the complex source
impedance.

Note that a complex impedance has a frequency dependant part.



Note the the definition of VSWR uses the magnitude of the reflection
coefficient, |r|, which removes the phase and frequency dependant parts.

Jeff

The magnitude DEPENDS on the frequency dependant parts.


But the ratio of Vmax/Vmin does not.

So what?

P=E^2/R; does that mean current is irrelevant to power?

There is no one, true, written in stone, official and holy definition
of SWR.

All the definitions are equally valid.



--
Jim Pennino

rickman wrote:
On 7/9/2015 3:03 PM, John S wrote:
On 7/9/2015 12:40 PM, wrote:
Jeff wrote:
On 08/07/2015 19:14, wrote:
John S wrote:
On 7/7/2015 1:44 PM, wrote:
Ian Jackson wrote:
In message , Jerry Stuckle
writes


Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there.

If there's no reflection, there can be no standing wave. So, being
pedantic, there's no such thing as an SWR of 1:1!

Despite the name, VSWR is defined in terms of complex impedances
and wavelengths, not "waves" of any kind.



Actually, VSWR is defined as the ratio of Vmax/Vmin.

Actually, VSWR can be defined several ways, one of which is:

(1 + |r|)/(1 - |r|)

Where r is the reflection coefficient which can be defined a:

(Zl - Zo)/(Zl + Zo)

Where Zl is the complex load impedance and Zo is the complex source
impedance.

Note that a complex impedance has a frequency dependant part.



Note the the definition of VSWR uses the magnitude of the reflection
coefficient, |r|, which removes the phase and frequency dependant parts.

Jeff

The magnitude DEPENDS on the frequency dependant parts.


But the ratio of Vmax/Vmin does not.

Huh? I'm pretty sure the VSWR is a function of frequency. A great deal
about the impedances *and* the voltages change with frequency.

A simple fact that totally eludes him.

SWR is a quality of an impedance match at a specified point in a system
and at a specified frequency.


--
Jim Pennino

"rickman" wrote in message
...
The magnitude DEPENDS on the frequency dependant parts.


But the ratio of Vmax/Vmin does not.

Huh? I'm pretty sure the VSWR is a function of frequency. A great deal
about the impedances *and* the voltages change with frequency.
--

Rick

The SWR is measured at a fixed frequency , so the formular is frequency
independant. Each time you change frequencies , the SWR will usually
change.

I guess that it all depends on how you look at it. You can use a sweep
generator and spectrum analizer to get a SWR curve over a frequency range.
If you feed a dummy load of pure resistance, it will not mater what
frequency you use, the swr will stay the same. If the load has an
impedance that is not constant at all frequencies, then the swr will change
as the frequency changes.

"rickman" wrote in message
...

Why do you ignore it when it says Zo is the impedance of the
transmission line and not the source?

I don't; The transmission line in this case IS the source.

No, the source is the source. Even if you wish to consider transmission
line as the source in some example, the page clearly says Zo is the
impedance of the transmission line, without any context where you can say
it is a source or a load.

https://en.wikipedia.org/wiki/Charac...ion_line_model


The SWR in a system, any kind of system, is measured at a point in a
system.

You mean a system that includes a source, a transmission line and a load?


One side of that point is the source and the other side of that point
is the load.

It also does not matter which side you declare the source and which side
you declare the load.

In that case the antenna is Zo? I don't think so.


A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source
and a 50 Ohm load.

By convention the load side is normally taken as the side which, when
the system is powered, the power is desired to be dissipated.

I don't know why you dig your heels in on every little point. Sometimes
you are just wrong and need to acknowledge that so the discussion can move
on. Zo (or Z0) is used to represent the characteristic impedance of a
transmission line. Zs (or Zsource) is used for the source. ZL (or Zload)
is used for the load. Read the wiki quote above and the many other
*clear* examples.

--

Rick

I think that is his problem. The source does not mater . It is just there
to provide power to the load. The swr is stated TOWARD the SOURCE. It does
not have anything to do with the actual source impedance. As someone said
eairler you measure the swr, then put any value resistor in parallel with
the transmitter (source) and measuer the swr. It will still be the same if
nothing else changes.

Jimp just can not seem to get it in his head the impedance of the
transmitter (source) does not matter. It seems to me he thinks the coax is
the source. I just don't see the coax generating any power outside of a
very minute random power depending on the temperature that would be in the
micro watts or less that is way out of the scope of the swr discussion.

rickman wrote:
On 7/9/2015 3:05 PM, wrote:
rickman wrote:
On 7/9/2015 1:58 PM, wrote:
rickman wrote:
On 7/9/2015 9:14 AM, Ralph Mowery wrote:
"Jeff" wrote in message
...

The SWR has to be the same at any point on the coax or transmission line
minus the loss in the line. A simple swr meter may show some differance
because of the way that kind of meter works. By changing the length of
the
line , the apparent SWR may be differant at that point.

There is no such thing as apparent SWR. It is what it is in a given
place.


By 'apparent SWR' he means as indicated SWR on the meter, and yes it can
change at various point on the line due to inadequacies in the meter; the
'real' VSWR will of course remain the same at any point on a lossless
line.

Jeff

That is what I mean Jeff. If there is any SWR, by changing the length of
the line, the voltage/current changes in such a maner that at certain points
you may get a 50 ohm match at that point.

https://en.wikipedia.org/wiki/Standi...dance_matching

"if there is a perfect match between the load impedance Zload and the
source impedance Zsource=Z*load, that perfect match will remain if the
source and load are connected through a transmission line with an
electrical length of one half wavelength (or a multiple of one half
wavelengths) using a transmission line of any characteristic impedance Z0."

This wiki article has a lot of good info in it. I have seen a lot of
stuff posted here that this article directly contradicts.... I wonder
who is right?

It has been my observation that when the subject matter is long established
science, such as transmission line theory, wiki is normally correct.

Why do you ignore it when it says Zo is the impedance of the
transmission line and not the source?

I don't; The transmission line in this case IS the source.

No, the source is the source. Even if you wish to consider transmission
line as the source in some example, the page clearly says Zo is the
impedance of the transmission line, without any context where you can
say it is a source or a load.

No, in THIS case the transmission is the source.

If you connect a transmitter to a power amplifier with cable so short
the transmission line effects are negliable, you STILL have a SWR
at the point between the two.

It is numerically irrelevant which end you designate the source and
which end you designate the load; the SWR at that point is the same
either way.

https://en.wikipedia.org/wiki/Charac...ion_line_model


The SWR in a system, any kind of system, is measured at a point in a system.

You mean a system that includes a source, a transmission line and a load?

I mean ANY system.

From a practical point of view, there is not much point in calculating
a SWR anywhere if there is not a source of energy somewhere that
eventually winds up in a load to be dissipated, but it is still a
perfectly valid calculation.

Here's an example of a more complex system one can actually find in
an Amateur station:

A transmitter is connected to a power amplifier through a coas transmission
line. The amplifier is connected through a coax transmission line to
a unbalanced to balanced transformer. The transmformer is connected to
a balanced transmission line to an antenna.

There is no SWR for the system. The SWR is meansured at a POINT in
the system.


One side of that point is the source and the other side of that point
is the load.

It also does not matter which side you declare the source and which side
you declare the load.


In that case the antenna is Zo? I don't think so.

Too bad; you are wrong.

A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source
and a 50 Ohm load.

By convention the load side is normally taken as the side which, when
the system is powered, the power is desired to be dissipated.

I don't know why you dig your heels in on every little point. Sometimes
you are just wrong and need to acknowledge that so the discussion can
move on. Zo (or Z0) is used to represent the characteristic impedance
of a transmission line. Zs (or Zsource) is used for the source. ZL (or
Zload) is used for the load. Read the wiki quote above and the many
other *clear* examples.

The source impedance is USUALLY a transmission line, but does not HAVE
to be.

The source impdedance could be the output of a matching section made
of lumped components.

WHAT the source and WHAT the load is physically does not matter.

If you are using a VNA to measure SWR, the source is whatever you connect
to the source port and the load is whatever you connect to the load port.


--
Jim Pennino

On 7/9/2015 3:50 PM, Ralph Mowery wrote:
"rickman" wrote in message
...
The magnitude DEPENDS on the frequency dependant parts.


But the ratio of Vmax/Vmin does not.

Huh? I'm pretty sure the VSWR is a function of frequency. A great deal
about the impedances *and* the voltages change with frequency.
--

Rick

The SWR is measured at a fixed frequency , so the formular is frequency
independant. Each time you change frequencies , the SWR will usually
change.

I think that is the definition of "frequency dependent".


I guess that it all depends on how you look at it. You can use a sweep
generator and spectrum analizer to get a SWR curve over a frequency range.
If you feed a dummy load of pure resistance, it will not mater what
frequency you use, the swr will stay the same. If the load has an
impedance that is not constant at all frequencies, then the swr will change
as the frequency changes.

I'm not going to debate the fine details of the subject. Anyone can
believe anything they wish. But the bottom line is that the SWR depends
on the components used in the system which, in any useful SWR
measurement, will give you a frequency dependent value.

The SWR using a dummy (purely resistive) load will not depend on
frequency, but it also won't tell you a thing about your antenna system.

--

Rick

On 7/9/2015 4:00 PM, Ralph Mowery wrote:
"rickman" wrote in message
...

Why do you ignore it when it says Zo is the impedance of the
transmission line and not the source?

I don't; The transmission line in this case IS the source.

No, the source is the source. Even if you wish to consider transmission
line as the source in some example, the page clearly says Zo is the
impedance of the transmission line, without any context where you can say
it is a source or a load.

https://en.wikipedia.org/wiki/Charac...ion_line_model


The SWR in a system, any kind of system, is measured at a point in a
system.

You mean a system that includes a source, a transmission line and a load?


One side of that point is the source and the other side of that point
is the load.

It also does not matter which side you declare the source and which side
you declare the load.

In that case the antenna is Zo? I don't think so.


A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source
and a 50 Ohm load.

By convention the load side is normally taken as the side which, when
the system is powered, the power is desired to be dissipated.

I don't know why you dig your heels in on every little point. Sometimes
you are just wrong and need to acknowledge that so the discussion can move
on. Zo (or Z0) is used to represent the characteristic impedance of a
transmission line. Zs (or Zsource) is used for the source. ZL (or Zload)
is used for the load. Read the wiki quote above and the many other
*clear* examples.

--

Rick

I think that is his problem. The source does not mater . It is just there
to provide power to the load. The swr is stated TOWARD the SOURCE. It does
not have anything to do with the actual source impedance. As someone said
eairler you measure the swr, then put any value resistor in parallel with
the transmitter (source) and measuer the swr. It will still be the same if
nothing else changes.

Jimp just can not seem to get it in his head the impedance of the
transmitter (source) does not matter. It seems to me he thinks the coax is
the source.

So he is agreeing with you that the source is not relevant. What is
relevant is the transmission line impedance.


I just don't see the coax generating any power outside of a
very minute random power depending on the temperature that would be in the
micro watts or less that is way out of the scope of the swr discussion.

Then don't bother to talk about it. I know I won't.

--

Rick

In article ,
wrote:

So what?

P=E^2/R; does that mean current is irrelevant to power?

There is no one, true, written in stone, official and holy definition
of SWR.

All the definitions are equally valid.

"SWR is a little tweeting bird chirping in a meadow. SWR is a wreath
of flowers which smell BAD. Are you sure your circuits are
registering properly? Your ears are green."

(Spock, "I, Mudd", 1967) (slightly misquoted)

Ralph Mowery wrote:

"rickman" wrote in message
...

Why do you ignore it when it says Zo is the impedance of the
transmission line and not the source?

I don't; The transmission line in this case IS the source.

No, the source is the source. Even if you wish to consider transmission
line as the source in some example, the page clearly says Zo is the
impedance of the transmission line, without any context where you can say
it is a source or a load.

https://en.wikipedia.org/wiki/Charac...ion_line_model


The SWR in a system, any kind of system, is measured at a point in a
system.

You mean a system that includes a source, a transmission line and a load?


One side of that point is the source and the other side of that point
is the load.

It also does not matter which side you declare the source and which side
you declare the load.

In that case the antenna is Zo? I don't think so.


A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source
and a 50 Ohm load.

By convention the load side is normally taken as the side which, when
the system is powered, the power is desired to be dissipated.

I don't know why you dig your heels in on every little point. Sometimes
you are just wrong and need to acknowledge that so the discussion can move
on. Zo (or Z0) is used to represent the characteristic impedance of a
transmission line. Zs (or Zsource) is used for the source. ZL (or Zload)
is used for the load. Read the wiki quote above and the many other
*clear* examples.

--

Rick

I think that is his problem. The source does not mater . It is just there
to provide power to the load. The swr is stated TOWARD the SOURCE. It does
not have anything to do with the actual source impedance. As someone said
eairler you measure the swr, then put any value resistor in parallel with
the transmitter (source) and measuer the swr. It will still be the same if
nothing else changes.

Jimp just can not seem to get it in his head the impedance of the
transmitter (source) does not matter. It seems to me he thinks the coax is
the source. I just don't see the coax generating any power outside of a
very minute random power depending on the temperature that would be in the
micro watts or less that is way out of the scope of the swr discussion.

Nope.

SWR is a measure of the impedance match at a point in a system.

It does not matter what the physical ends are.

One end could be an unbalanced to balanced transformation network and the
other end a length of parallel transmission line.

If the impedance of the tranmitter does not matter, than connect YOUR
transmitter to a length of 95 Ohm coax which is terminated in a
square loop with an impedance of 110 Ohms.

What is the SWR at the point between the coax and loop? What is the
source and what is the load?

What is the SWR at the point beteen the transmitter and the coax? What is the
source and what is the load?



--
Jim Pennino

rickman wrote:
On 7/9/2015 4:00 PM, Ralph Mowery wrote:
"rickman" wrote in message
...

Why do you ignore it when it says Zo is the impedance of the
transmission line and not the source?

I don't; The transmission line in this case IS the source.

No, the source is the source. Even if you wish to consider transmission
line as the source in some example, the page clearly says Zo is the
impedance of the transmission line, without any context where you can say
it is a source or a load.

https://en.wikipedia.org/wiki/Charac...ion_line_model


The SWR in a system, any kind of system, is measured at a point in a
system.

You mean a system that includes a source, a transmission line and a load?


One side of that point is the source and the other side of that point
is the load.

It also does not matter which side you declare the source and which side
you declare the load.

In that case the antenna is Zo? I don't think so.


A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source
and a 50 Ohm load.

By convention the load side is normally taken as the side which, when
the system is powered, the power is desired to be dissipated.

I don't know why you dig your heels in on every little point. Sometimes
you are just wrong and need to acknowledge that so the discussion can move
on. Zo (or Z0) is used to represent the characteristic impedance of a
transmission line. Zs (or Zsource) is used for the source. ZL (or Zload)
is used for the load. Read the wiki quote above and the many other
*clear* examples.

--

Rick

I think that is his problem. The source does not mater . It is just there
to provide power to the load. The swr is stated TOWARD the SOURCE. It does
not have anything to do with the actual source impedance. As someone said
eairler you measure the swr, then put any value resistor in parallel with
the transmitter (source) and measuer the swr. It will still be the same if
nothing else changes.

Jimp just can not seem to get it in his head the impedance of the
transmitter (source) does not matter. It seems to me he thinks the coax is
the source.

So he is agreeing with you that the source is not relevant. What is
relevant is the transmission line impedance.

Place a lumped component matching network between the transmission
line and the antenna.

What is the source at the point between the line and the network?

What is the source at the point between the network and the antenna?


--
Jim Pennino