An apparatus comprises: radio frequency (RF) transceiver circuitry for electrical coupling to an antenna and including: a local oscillator (LO) circuit configured to generate a LO signal, and a mixer circuit configured to mix a CW tone signal with the LO signal; a measurement receiver path configured to measure an antenna signal, wherein the antenna signal includes the CW tone signal mixed with the LO signal; and baseband processing circuitry electrically coupled to the measurement receiver path and configured to adjust a clock duty ratio of the LO signal to reduce one or more counter intermodulation (CIM) signals in the antenna signal.