1. Technical Field
The present invention relates to passive intermodulation (PIM) and systems and methods for measuring PIM in a network and/or device.
2. Related Art
Passive intermodulation (PIM) causes an unwanted signal or signals to be generated by the non-linear mixing of two or more frequencies in a passive device such as a connector or cable. PIM has surfaced as a problem for cellular telephone technologies including Global System for Mobile Communications (GSM), Advanced Wireless Service (AWS) and Personal Communication Service (PCS) systems. Cable assemblies connecting a base station to an antenna on a tower using these cellular systems typically have multiple connectors that can act as sources of PIMs that interfere with system operation.
PIM signals are created when two signals from different systems or the same system combine and are then reflected at a PIM point such as a faulty cable connector. If the generated PIM harmonic frequency components fall within the receive band of a base station, it can effectively block a channel and make the base station receiver think that a carrier is present when one is not. Generally the components of concern are third, fifth, and seventh order, where the third order is of greatest signal strength, and therefore, of primary concern. PIMs can occur when two base stations operating at different frequencies, such as an AWS device and a PCS device, are in close proximity.
PIMs can be reduced or eliminated by replacing faulty cables or connectors. Test systems exist for determining the distance and magnitude to sources of PIMs, allowing a technician to locate and replace the faulty cable or connector. A test system to measure PIMs creates signals at two different frequencies, amplifies them, and provides them through cables connecting a base station to antennas on a tower for the base stations. A return signal carrying the PIMs is filtered to select a desired test frequency harmonic where PIMs can be detected and the PIM and distance to PIM measurement is provided to an operator. What are needed are improved systems and methods for determining the magnitude of and distance to PIM sources.