Passive intermodulation (PIM) arises when there are two or more signals present in a passive non-linear device. Interference caused by PIM decreases a cell's receive sensitivity and can block phone calls completely. Consequently, PIM is a serious issue for cellular providers because it decreases the reliability, data rate, and capacity of their networks. It can be very challenging to find the source of PIM because it can be caused by internal factors (damaged or loose cables, dirty connectors, etc.) as well as external factors (fences, metal-to-metal contact, rusty bolts, etc.).
When the cause of PIM is unknown, technicians can use PIM hunting test equipment to pinpoint the source within centimeters. This is done by a PIM tester that uses two high-power test signals to broadcast through the site antenna revealing any PIM sources in the RF path. By using a PIM probe connected to a spectrum analyzer, a technician can see the precise location of the PIM source. This is seen when the PIM probe comes close to the PIM source and increases the PIM value by as much as 30 dB. The use of PIM hygiene products is essential when hunting for PIM. These products act as RF barriers and help isolate and reduce external PIM.