Since I don't have a load pull handy, I thought of a comparative measurement to see if there really is a difference in source impedance between different power levels:
Connect the source to a terminated directional coupler and measure the return loss from the In_Cpl/Out_Cpl power difference with an Spec Analyzer or power meter(diagram)
I know this is not accurate but I should be able to detect a change in the source impedance.
Does this make good sense?
What specs do I need in the directional coupler to get the best results out of this? does this do the job?
https://www.minicircuits.com/WebStore/dashboard.html?model=ZABDC10-25HP-S
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