As passive intermodulation is a parameter that is key to the operation of many systems including cellular base stations, satellite systems and many other radio systems were duplex operation is required, passive intermodulation, PIM testing is required. 

Passive intermodulation, PIM arises when non-linear passive components or other general elements like rusty bolts on antenna towers, etc, enable two or more signals to mix or multiply to give intermodulation distortion.

One of the most common PIM testing applications is for antennas and antenna feeder arrangements for cellular base stations. Here some of the major issues with PIM occur as a result of connectors, connections, and even the feeder for antennas themselves.