I am developing a 10.7 MHz IF amplifier for a radio receiver. In order to match the input to the output of the driving mixer stage (330 ohm) I need to measure the input impedance.
I did the measurement with a NanoVNA (I don't have access to a professional VNA), that I bought via the well known Chinese website. Though I have reasons to believe the Nano is reasonably accurate, the problem that I encounter is that the output level of the VNA drives the amplifier way past it's 1 dB compression point, so it is unsure if the measurement is correct. The capabilities of the NanoVNA are very limited, and it may not be possible to reduce the power level internally.
I read a suggestion to pad the S11 output with a T or PI pad attenuator, and use the output of the pad as reference plane, so in effect do the OSL calibration behind the pad:
Is padding the output like this a common approach, and will the measurements be sufficiently accurate? I estimate the required attenuation to be 10 up to 20 dB.