Roger Hayter wrote:
wrote:

John S wrote:
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*.

Which, as in most cases is purchased and has a fixed impedance of 50
Ohms, and thus defines the system impedance.

Please find one specification for a transmitter that says it *has* an
output impedance of 50 ohms. You will find plenty that say they are
designed to drive a load impedance of 50 ohms, but few that state their
output impedance. Of those I have seen that do, none are amateur
transmitters and the impedance they mention is much lower than 50 ohms.

Notice I did not use the word "transmitter" in my post.

I was speaking from an engineering point of view, not from an Amateur
radio operator point of view.

Notice that the post I was responding to used the words "engineer", not
"Amateur" and "generator" not "transmitter".



--
Jim Pennino