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