How do I identify passive intermodulation sources in an installed antenna system?

Passive intermodulation (PIM) in an installed antenna system is caused by nonlinear junctions in the passive RF signal path that generate intermodulation products when high-power transmit signals pass through them. Unlike active intermodulation (from amplifiers), PIM is created by passive components and structures that should be linear but exhibit slight nonlinearity due to: loose or corroded connector contacts (the metal-oxide-metal junction at poorly mated connectors creates a nonlinear resistance similar to a diode), dissimilar metal junctions (contact between different metals, such as copper and aluminum, or steel and brass, creates thermoelectric effects that generate nonlinear mixing), rusty or corroded components (iron oxide is a semiconductor that creates nonlinear junctions when it forms at contact points), cracked solder joints (fractured solder creates intermittent metal-to-metal contacts), and nearby metallic objects in the antenna field (loose hardware, metal flashing, guy wires, or other metal objects near the antenna that are illuminated by the transmitted signal can re-radiate PIM products). PIM is a critical problem in cellular base stations where the IM products from multiple transmit carriers fall in the receive band, desensitizing the receiver. Identification involves: measuring PIM with a calibrated PIM analyzer (transmitting two high-power CW tones and measuring the IM3 product level at the antenna port), then systematically isolating sections of the antenna system to locate the source (disconnect and test individual components: jumper cables, surge protectors, connectors, and the antenna itself).