On Sun, Dec 29, 2024 at 05:57 PM, Andrew Love wrote:

Of course the real question here is possibly why is there a mismatch  between
the output of the qcx and the input of the amp?

Driving a non-class A amplifier is complicated. For one thing, the input impedance varies significantly with supply voltage and drive/power level, and to some extent the output tuning........
2:1 VSWR is a common spec limit. Consider the situation where the source is 100Ω and the load is 25Ω, there is a 4:1 mismatch yet both are "nominally" 50Ω. Power transfer will clearly not be optimum.

For another, the output impedance also varies and the output power and efficiency varies with the load, even more than just the mismatch loss would suggest.
Even the impedance at the 2nd, 3rd and possibly higher harmonics will have significant effects, at both input and output.

You might get more than power with 50Ω, you might get less, it depends on the amplifier and its tuning and bias conditions.
Many of these same effects will occur with the driving amplifier/transmitter.
Things get complicated when you are driving a dynamic, nonlinear load with a similarly imperfect source.

https://en.wikipedia.org/wiki/Load_pull https://www.everythingrf.com/community/what-are-load-pull-measurements
73, Don N2VGU