Brian Reay wrote:
On 08/07/15 19:36, wrote:
Brian Reay wrote:
wrote:
Brian Reay wrote:
On 06/07/15 01:21, wrote:
John S wrote:
On 7/5/2015 5:24 PM, wrote:
Roger Hayter wrote:
wrote:


The output impedance of an amateur transmitter IS approximately 50 Ohms
as is trivially shown by reading the specifications for the transmitter
which was designed and manufactured to match a 50 Ohm load.

Do you think all those manuals are lies?

You are starting with a false premise which makes everything after that
false.


A quick google demonstrates dozens of specification sheets that say the
transmitter is designed for a 50 ohm load, and none that mention its
output impedance.

If the source impedance were other than 50 Ohms, the SWR with 50 Ohm
coax and a 50 Ohm antenna would be high. It is not.

Where is the source impedance found on a Smith chart? Also, if you have
EZNEC, you will not find a place to specify source impedance but it will
show the SWR.

A Smith chart is normalized to 1.

That is true but is doesn't address the point. There should still be
somewhere to represent the source impedance, albeit normalised.

The purpose of a Smith chart it to match a SOURCE to a LOAD.

EZNEC allows you to set the impedance to anything you want and assumes
the transmission line matches the transmitter.

Likewise, that is a sweeping statement which evades the point.

The main purpose of EZNEC is to design an antenna for amateur radio use
and all commercial amateur radio transmitters have an output impedance
of 50 Ohms.


Neither of those responses address the points.

It is clear you cannot support your assertions.

EZNEC can set the source impedance to any value one desires, but the
default is 50 Ohms as most people are interested in 50 Ohm systems
as the majority of transmitters are designed for 50 Ohm loads.

EZNEC calculates the SWR for an antenna presented to the SOURCE
in the model.

For most simulations, the SOURCE is placed at the antenna terminals,
which represents what an attached transmission line will see.

The transmission line most commonly used is 50 Ohm coax.

EZNEC will also allow you to put a SOURCE at one end of a transmission
line with the other end of the line at the antenna terminals.

In this simulation, EZNEC simulates what the transmitter would see if
it were connected to the transmission line/antenna system.

SWR is defined in terms of SOURCE impedance and LOAD impedance.

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

Where r = reflection coefficient and

r = (Zl - Zo)/(Zl + Zo)

Where Zl = complex load impedance, Zo = complex source impedance.



The matter at hand isn't SWR it is the output impedance of PAs.

Nope, the matter at hand is the definition of SWR.


That seems to be you sticking point. You are assuming the PA is a
transmission line, rather than an active source.

Nope, the matter at hand is the definition of SWR, which is defined
in terms of SOURCE impedance and LOAD impedance.

It does not matter in the slightest if the SOURCE impedance is the
output of a transmitter or the end of a transmission line.

You confusion isn't helped by the habit of some manufacturers including
SWR in the PA spec.

Manufacturers specify the LOAD impedance for the transmitter, and
sometimes the SWR range that the transmitter will handle.

Modern PAs are designed to drive a load of 50 ohms, they don't have a
source impedance of 50 ohms. If they are driven into the wrong load,
they can operated outside there safe area of operation. If the power
isn't reduced, they can be damaged.

Once again, SWR is defined in terms of SOURCE impedance and LOAD
impedance. The normal LOAD for a transmitter is one end of a piece
of coax with an antenna on the other end.

The SWR at the near end of a piece of coax may or may not be the
same as the SWR at the far end of the coax.


--
Jim Pennino

wrote in message
...

Once again, SWR is defined in terms of SOURCE impedance and LOAD
impedance. The normal LOAD for a transmitter is one end of a piece
of coax with an antenna on the other end.

The SWR at the near end of a piece of coax may or may not be the
same as the SWR at the far end of the coax.


--
Jim Pennino

Can you show any place where the SWR definition mentions the Source
impedance ?

I have never seen anything that mentions the Source impedance. Just the
ratio of the voltage or current going forward and reflected.

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.

Ralph Mowery wrote:

wrote in message
...

Once again, SWR is defined in terms of SOURCE impedance and LOAD
impedance. The normal LOAD for a transmitter is one end of a piece
of coax with an antenna on the other end.

The SWR at the near end of a piece of coax may or may not be the
same as the SWR at the far end of the coax.


--
Jim Pennino

Can you show any place where the SWR definition mentions the Source
impedance ?

I have several times now, but once again:

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

Where r = reflection coefficient.

r = (Zl - Zo)/(Zl + Zo)

Where Zl = complex load impedance and Zo = complex source impedance.

https://en.wikipedia.org/wiki/Reflection_coefficient

http://www.antenna-theory.com/tutori...nsmission3.php

I have never seen anything that mentions the Source impedance. Just the
ratio of the voltage or current going forward and reflected.

It is generally not mentioned in Amateur publications.

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.

Transmission line transformers.

http://highfrequencyelectronics.com/...TraskPart2.pdf

Impedance matching.

https://en.wikipedia.org/wiki/Impedance_matching


--
Jim Pennino

wrote in message
news
Ralph Mowery wrote:


Can you show any place where the SWR definition mentions the Source
impedance ?

I have several times now, but once again:

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

Where r = reflection coefficient.

r = (Zl - Zo)/(Zl + Zo)

Where Zl = complex load impedance and Zo = complex source impedance.

https://en.wikipedia.org/wiki/Reflection_coefficient

http://www.antenna-theory.com/tutori...nsmission3.php


YOu have just proven my point. Read carefully from your refernce to
Wikipedia :

"The reflection coefficient of a load is determined by its impedance and
the impedance toward the source."

Notice it says TOWARD and not THE SOURCE.

From the second referaence notice that it says load impedance and impedance
of the transmission line. Nothing mentions the source at all:

"The reflection coefficient is usually denoted by the symbol gamma. Note
that the magnitude of the reflection coefficient does not depend on the
length of the line, only the load impedance and the impedance of the
transmission line. Also, note that if ZL=Z0, then the line is "matched". In
this case, there is no mismatch loss and all power is transferred to the
load."

Ralph Mowery wrote:

wrote in message
news
Ralph Mowery wrote:


Can you show any place where the SWR definition mentions the Source
impedance ?

I have several times now, but once again:

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

Where r = reflection coefficient.

r = (Zl - Zo)/(Zl + Zo)

Where Zl = complex load impedance and Zo = complex source impedance.

https://en.wikipedia.org/wiki/Reflection_coefficient

http://www.antenna-theory.com/tutori...nsmission3.php


YOu have just proven my point. Read carefully from your refernce to
Wikipedia :

"The reflection coefficient of a load is determined by its impedance and
the impedance toward the source."

Notice it says TOWARD and not THE SOURCE.

Notice it actually says "the impedance toward the source".

From the second referaence notice that it says load impedance and impedance
of the transmission line. Nothing mentions the source at all:

What the hell do you think the transmission line is in this case if
not the source?

"The reflection coefficient is usually denoted by the symbol gamma. Note
that the magnitude of the reflection coefficient does not depend on the
length of the line, only the load impedance and the impedance of the
transmission line. Also, note that if ZL=Z0, then the line is "matched". In
this case, there is no mismatch loss and all power is transferred to the
load."

Perhaps you would like the second link better as it has pictures.

Of maybe this one that explains it all starting with lumped equivelant
circuits.

http://www.maximintegrated.com/en/ap...dex.mvp/id/742

Notice that ALL the links talk about the source impedance.



--
Jim Pennino

On 7/8/2015 6:43 PM, wrote:
Ralph Mowery wrote:

wrote in message
news
Ralph Mowery wrote:


Can you show any place where the SWR definition mentions the Source
impedance ?

I have several times now, but once again:

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

Where r = reflection coefficient.

r = (Zl - Zo)/(Zl + Zo)

Where Zl = complex load impedance and Zo = complex source impedance.

https://en.wikipedia.org/wiki/Reflection_coefficient

http://www.antenna-theory.com/tutori...nsmission3.php


YOu have just proven my point. Read carefully from your refernce to
Wikipedia :

"The reflection coefficient of a load is determined by its impedance and
the impedance toward the source."

Notice it says TOWARD and not THE SOURCE.

Notice it actually says "the impedance toward the source".

From the second referaence notice that it says load impedance and impedance
of the transmission line. Nothing mentions the source at all:

What the hell do you think the transmission line is in this case if
not the source?

"The reflection coefficient is usually denoted by the symbol gamma. Note
that the magnitude of the reflection coefficient does not depend on the
length of the line, only the load impedance and the impedance of the
transmission line. Also, note that if ZL=Z0, then the line is "matched". In
this case, there is no mismatch loss and all power is transferred to the
load."

Perhaps you would like the second link better as it has pictures.

Of maybe this one that explains it all starting with lumped equivelant
circuits.

http://www.maximintegrated.com/en/ap...dex.mvp/id/742

Notice that ALL the links talk about the source impedance.

So, you are saying Zo is the source impedance while every one else
thinks it is the characteristic impedance of the line. Go back to your
books and look up the definition of Zo.

John S wrote:
On 7/8/2015 6:43 PM, wrote:
Ralph Mowery wrote:

wrote in message
news Ralph Mowery wrote:


Can you show any place where the SWR definition mentions the Source
impedance ?

I have several times now, but once again:

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

Where r = reflection coefficient.

r = (Zl - Zo)/(Zl + Zo)

Where Zl = complex load impedance and Zo = complex source impedance.

https://en.wikipedia.org/wiki/Reflection_coefficient

http://www.antenna-theory.com/tutori...nsmission3.php


YOu have just proven my point. Read carefully from your refernce to
Wikipedia :

"The reflection coefficient of a load is determined by its impedance and
the impedance toward the source."

Notice it says TOWARD and not THE SOURCE.

Notice it actually says "the impedance toward the source".

From the second referaence notice that it says load impedance and impedance
of the transmission line. Nothing mentions the source at all:

What the hell do you think the transmission line is in this case if
not the source?

"The reflection coefficient is usually denoted by the symbol gamma. Note
that the magnitude of the reflection coefficient does not depend on the
length of the line, only the load impedance and the impedance of the
transmission line. Also, note that if ZL=Z0, then the line is "matched". In
this case, there is no mismatch loss and all power is transferred to the
load."

Perhaps you would like the second link better as it has pictures.

Of maybe this one that explains it all starting with lumped equivelant
circuits.

http://www.maximintegrated.com/en/ap...dex.mvp/id/742

Notice that ALL the links talk about the source impedance.

So, you are saying Zo is the source impedance while every one else
thinks it is the characteristic impedance of the line. Go back to your
books and look up the definition of Zo.

When a transmission line is connected to a load, the source for the load
IS the end of the transmission line.

Where else would you think the source is?

Instead of arguing about it, one can download QUCS for free which
will simulate the whole thing and one can see what really happens.

Download QUCS for your operating system:

http://qucs.sourceforge.net/

Generate a model consisting of a voltage source with a series resistance
of a few Ohms to simulate a solid state source or a much higher
resistance to simulate a vacuum tube source. Chose a convienient
frequency for the simulation.

Go to: http://home.sandiego.edu/~ekim/e194r.../matcher2.html
to calculate an impedance matching network to match the resistance
you've chosen to 50 Ohms at the choosen frequency.

Put the matching circuit in the model.

Add a 50 Ohm transmission line to the model.

Terminate the transmission line with a 50 Ohm resistor.

Add a fixed frequency AC simulation at the choosen frequency.

Change various parameters to your heart's content to see what happens.

Change the matching network such that the output of your transmitter
is no longer 50 Ohms and see what happens.

When the QUCS output disagrees with your beliefs, you can argue with
the program.


--
Jim Pennino

On 7/8/2015 7:43 PM, wrote:
Ralph Mowery wrote:

wrote in message
news
Ralph Mowery wrote:


Can you show any place where the SWR definition mentions the Source
impedance ?

I have several times now, but once again:

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

Where r = reflection coefficient.

r = (Zl - Zo)/(Zl + Zo)

Where Zl = complex load impedance and Zo = complex source impedance.

https://en.wikipedia.org/wiki/Reflection_coefficient

http://www.antenna-theory.com/tutori...nsmission3.php

You might check that again. I don't see Zo being defined as the complex
source impedance, but rather as the transmission line characteristic
impedance... not the same thing at all.


YOu have just proven my point. Read carefully from your refernce to
Wikipedia :

"The reflection coefficient of a load is determined by its impedance and
the impedance toward the source."

Notice it says TOWARD and not THE SOURCE.

Notice it actually says "the impedance toward the source".

From the second referaence notice that it says load impedance and impedance
of the transmission line. Nothing mentions the source at all:

What the hell do you think the transmission line is in this case if
not the source?

"The reflection coefficient is usually denoted by the symbol gamma. Note
that the magnitude of the reflection coefficient does not depend on the
length of the line, only the load impedance and the impedance of the
transmission line. Also, note that if ZL=Z0, then the line is "matched". In
this case, there is no mismatch loss and all power is transferred to the
load."

Perhaps you would like the second link better as it has pictures.

Of maybe this one that explains it all starting with lumped equivelant
circuits.

http://www.maximintegrated.com/en/ap...dex.mvp/id/742

Notice that ALL the links talk about the source impedance.

How about this one?

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

I think this has some very interesting analysis, very specifically
referring to "purely resistive load impedance".

--

Rick

rickman wrote:
On 7/8/2015 7:43 PM, wrote:
Ralph Mowery wrote:

wrote in message
news Ralph Mowery wrote:


Can you show any place where the SWR definition mentions the Source
impedance ?

I have several times now, but once again:

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

Where r = reflection coefficient.

r = (Zl - Zo)/(Zl + Zo)

Where Zl = complex load impedance and Zo = complex source impedance.

https://en.wikipedia.org/wiki/Reflection_coefficient

http://www.antenna-theory.com/tutori...nsmission3.php

You might check that again. I don't see Zo being defined as the complex
source impedance, but rather as the transmission line characteristic
impedance... not the same thing at all.


YOu have just proven my point. Read carefully from your refernce to
Wikipedia :

"The reflection coefficient of a load is determined by its impedance and
the impedance toward the source."

Notice it says TOWARD and not THE SOURCE.

Notice it actually says "the impedance toward the source".

From the second referaence notice that it says load impedance and impedance
of the transmission line. Nothing mentions the source at all:

What the hell do you think the transmission line is in this case if
not the source?

"The reflection coefficient is usually denoted by the symbol gamma. Note
that the magnitude of the reflection coefficient does not depend on the
length of the line, only the load impedance and the impedance of the
transmission line. Also, note that if ZL=Z0, then the line is "matched". In
this case, there is no mismatch loss and all power is transferred to the
load."

Perhaps you would like the second link better as it has pictures.

Of maybe this one that explains it all starting with lumped equivelant
circuits.

http://www.maximintegrated.com/en/ap...dex.mvp/id/742

Notice that ALL the links talk about the source impedance.

How about this one?

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

I think this has some very interesting analysis, very specifically
referring to "purely resistive load impedance".

So what?

A purely resistive anything is a special case of the general problem.


--
Jim Pennino

"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.