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