A test method allows investigating the dependence of microwave gain, power and linearity behavior of transistors, in which modulated RF signal is injected, as a function of source and load impedance at the signal RF carrier frequency and its harmonics as well as at the modulation (baseband) IF frequency using passive programmable tuners. A calibration method allows synthesizing independently impedances at the various frequencies without the need of on-line vector signal measurement. The test setup performs independent impedance tuning at RF and IF frequencies of the modulated signal at the input and output of the DUT. This allows optimizing IF impedances for nonlinear amplifier performance with modulated signal, such as ACPR, EVM etc. IF tuning is done using a low frequency programmable impedance tuner inserted in the DC branch of the bias networks, which act as frequency diplexers.