On 7/9/2015 5:11 PM, wrote:
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?

Deep thoughts.... What is the sound of one hand clapping?

--

Rick

wrote in message ...

Wayne wrote:


wrote in message ...

John S wrote:
On 7/8/2015 7:27 PM, Wayne wrote:


"John S" wrote in message ...

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.

That's also my understanding of the definition.
In fact since SWR is defined as the maximum to minimum voltage ratio,
the "V" in VSWR is redundant.

Sort of. There is also ISWR but it is not used frequently.

# Not sort of, but is.

# There is also PSWR.

And both go back to the Vmax/Vmin definition.

The PSWR is a tricky one because you can end up with a power ratio instead
of a voltage ratio.

# Actually, no, PSWR has nothing to do with power ratios as in RF power,
# rather it has to do with power ratios as in values raised to the second
# power.

What I'm getting at is that the ratio of forward to reflected power needs a
bit more math to get to VSWR.

wrote:

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...nsmission_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.

No it is not. You don't get standing waves on 10mm of wire. (At HF
anyway). It is a property of a driven transmission line and depends
on the network at the far end. It is directional and does *not* depend
on the impedance of the source. (If you put a signal source at the far
end, in parallel with the existing load or replacing it, then you would
get a potentially quite different SWR due to the impedance of what was
the source. Because you would not have matched the source impedance to
the tansmission line impedance. In the general case, a network which
matches the impedance looking into the tansmission line to the impedance
desired by the source for a satisfactory working point willl *not* match
the source impadance to the transmission line characteristic impedance.
In the general case it will be impossible to match impedances in both
directions, and in pracitce we don't even try.



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?


--
Roger Hayter

Wayne wrote:


wrote in message ...

Wayne wrote:


wrote in message ...

John S wrote:
On 7/8/2015 7:27 PM, Wayne wrote:


"John S" wrote in message ...

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.

That's also my understanding of the definition.
In fact since SWR is defined as the maximum to minimum voltage ratio,
the "V" in VSWR is redundant.

Sort of. There is also ISWR but it is not used frequently.

# Not sort of, but is.

# There is also PSWR.

And both go back to the Vmax/Vmin definition.

The PSWR is a tricky one because you can end up with a power ratio instead
of a voltage ratio.

# Actually, no, PSWR has nothing to do with power ratios as in RF power,
# rather it has to do with power ratios as in values raised to the second
# power.

What I'm getting at is that the ratio of forward to reflected power needs a
bit more math to get to VSWR.

Yes, in terms of power:

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

Where Pf = forward power, Pr = reflected power.



--
Jim Pennino

rickman wrote:
On 7/9/2015 5:11 PM, wrote:
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?

Deep thoughts.... What is the sound of one hand clapping?

Try this: SWR like voltage is determined by two points.

In the case of voltage, the "other" point is usually ground, but can
be anything.

In the case of SWR, the "other" point is usually a transmission line,
but can be anything.



--
Jim Pennino

Roger Hayter wrote:
wrote:

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...nsmission_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.

No it is not. You don't get standing waves on 10mm of wire. (At HF
anyway). It is a property of a driven transmission line and depends
on the network at the far end.


In the case where you have a transmission line, but only where you have
a transmission line.

Connect an Amateur transmitter directly to one end of an SWR meter
and the other end of the meter to a 100 Ohm resitor. The frequency
is the bottom end of the 160 M band.

The SWR meter reads 2:1.

Where are the standing waves?


--
Jim Pennino

On 7/9/2015 12:32 AM, wrote:
John S wrote:
On 7/8/2015 4:48 PM, wrote:
John S wrote:
On 7/8/2015 12:47 PM, wrote:
John S wrote:

So, at 1Hz the law has changed, eh? What new law do I need to use?

To be pendatic, there is only one set of physical laws that govern
electromagnetics.

However for DC all the complex parts of those laws have no effect and
all the equations can be simplified to remove the complex parts.

In the real, practical world people look upon this as two sets of
laws, one for AC and one for DC.

A good example of this is the transmission line which does not exist
at DC; at DC a transmission line is nothing more than two wires with
some resistance that is totally and only due to the ohmic resistance
of the material that makes up the wires.

So, is .01Hz AC or DC, Jim? How about 1Hz? 10Hz? Where does AC begin and
DC end?

It is called a limit.

If there is NO time varying component, it is DC, otherwise it is AC.

Are you playing devil's advocate or are you really that ignorant?

Then there is no such thing as DC because even a battery looses voltage
over a period of time. DC voltage sources have noise.

An ideal battery doesn't.

Where can one be purchased?

On 7/9/2015 12:58 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.

Wiki is subject to the same errors you make because the information is
usually supplied by people like you.

On 7/9/2015 1:01 PM, wrote:
Jeff wrote:
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?


That is a very specific case where the source is not at the system
impedance and happens to be equal to the load impedance, there will also
be standing waves on the transmission line and associated losses as the
VSWR on the line will be equal to the magnitude of the mismatch between
the transmission line impedance and the load impedance.

Jeff

Most people take the source impdedance to be the system impedance, i.e.
the impedance for which everything else is designed for.

Most *engineers* take the source impedance to be the impedance of the
*generator*.

In fact, perhaps the rest of us should call it the generator rather than
the source so that we can communicate with you on your level.

John S wrote:
On 7/9/2015 12:32 AM, wrote:
John S wrote:
On 7/8/2015 4:48 PM, wrote:
John S wrote:
On 7/8/2015 12:47 PM, wrote:
John S wrote:

So, at 1Hz the law has changed, eh? What new law do I need to use?

To be pendatic, there is only one set of physical laws that govern
electromagnetics.

However for DC all the complex parts of those laws have no effect and
all the equations can be simplified to remove the complex parts.

In the real, practical world people look upon this as two sets of
laws, one for AC and one for DC.

A good example of this is the transmission line which does not exist
at DC; at DC a transmission line is nothing more than two wires with
some resistance that is totally and only due to the ohmic resistance
of the material that makes up the wires.

So, is .01Hz AC or DC, Jim? How about 1Hz? 10Hz? Where does AC begin and
DC end?

It is called a limit.

If there is NO time varying component, it is DC, otherwise it is AC.

Are you playing devil's advocate or are you really that ignorant?

Then there is no such thing as DC because even a battery looses voltage
over a period of time. DC voltage sources have noise.

An ideal battery doesn't.

Where can one be purchased?

At the ideal battery store.


--
Jim Pennino