Dr. Slick wrote:

As you might know, the input S11 or SWR will change when you go
from an antenna analyzer or network analyzer to measuring with the
actual full power PA and meter hooked up. This may be partly due to
the fact that the meter is usually not a perfect 50 ohm thru, and
partly due to the fact that the analyzers outputs are closer to 50
ohms than the PA.

If S11 or the SWR actually does change, you've either got a nonlinear
transmission line or a nonlinear load. That is, the impedance changes as
the signal level changes. If you *measure* a different SWR or S11, it
means that either the SWR or S11 is actually changing for the reasons I
just stated, or the meter is nonlinear in the sense that its reading
changes with power level (possibly due to RF ingress, but it could be a
host of other things), or you're measuring with two different meters
that don't agree.

It's not because of the different source impedances.

Sure, you can normalize a Smith chart to anything you'd like. That
doesn't make the SWR change with source impedance.

. . .

Roy Lewallen, W7EL