Abstract: A test set for an amplifier or other electronic device in which a waveform enerator furnishes a modulated RF signal to the item under test. Sensors extract samples of the RF signal at the item's input and output. A detector-mixer network compares and processes the input and output sample signals and produces signals at its output which are indicative of the phase distortion and amplitude distortion introduced by the item. The phase and amplitude distortion signals are sampled and held for each modulating signal pulse and are then processed to compile statistical data regarding the item's performance.