I'm trying to figure out how to back calculate the OIP3 of an amplifier by measuring it in a system with a mixer and then measuring the mixer itself.  I do see a difference (degradation) in the intermod products when I measure the mixer by itself vs. inserting the amp so I know the system IP3 is being effected by the amp.  I measure the mixer at the same power level input that the amp will put into it when inserted so I keep the level into the mixer the same.  Does anyone have any idea how to back calculate this?