PIM is a form of intermodulation distortion that occurs in passive components normally thought of as linear, such as filters, combiners, surge protectors, cables, connectors, and antennas. However, when subject to the high RF powers found in cellular systems, these devices can generate spurious signals.
PIM shows up as a set of unwanted signals created by the mixing of two or more strong RF signals in a non-linear device, such as in a loose or corroded connector, or in nearby rust. Other names for PIM include the "diode effect" and the "rusty bolt effect".
Many symptoms could be indicators of PIM problems. These include:
- Receiver desensitization (raised noise floor)
- Rx Diversity alarms
- Spectral re-growth in the transmitter mask
- Excessive dropped/blocked calls
- Cell site coverage shrinking
- Complaints of interference from neighboring cell site owners