A local oscillator (LO) of a test system is set to an initial frequency whereupon a device under test (DUT) transmits a radio frequency (RF) signal to the test system. Characteristics of the RF signal are measured with the test system and used to identify magnitudes and frequencies of spurious signal products. The LO of the test system is reset to one or more subsequent frequencies that are offset from the initial frequency. One or more subsequent RF signals are transmitted from the DUT to the test system, with the DUT maintaining its original signal settings. Characteristics of the subsequent RF signals are measured with the test system and used to identify magnitudes and frequencies of spurious signal products for each of the subsequent LO frequencies. The spurious signal products that have shifted in frequency for each of the subsequent LO frequencies as self-generated signal products can then be identified.