Transmission Network Planning

Internal and External PIM

BNN has the skill, competence and the equipment to hunt internal as well as external PIM for 2G, 3G and LTE based systems



Ques:What is PIM?

Ans:Passive intermodulation occurs when two or more signals are present in a passive non-linear device or element. The signals will mix or multiply with each other to generate other signals that are related to the first ones. PIM can occur even when no active components are present. PIM can occur in a variety of areas from coaxial connectors to cables, even rusty bolts or any joint where dissimilar metals occur. PIM can produce interference, and this can sometimes hide the wanted signal.

Ques:What are the types of PIM?

Ans:PIM could be Internal or External. Internal PIM is caused due to high power emission within own system due to damaged connectors, cables, duplexers, circulators, Jumper cables within the system. This can be detected, located and corrected using PIM testers. The External PIM occurs due to Intermodulation products generated externally due to presence of external high power emitters around the site due to nearby corroded objects, such as fences, barn roofs or rusty bolts. This can be detected but may not be located/ corrected with PIM testers

Ques:What is TAP test?

Ans:A Tap test is a simple test for detecting faulty connectors causing PIM. During the test, connectors are tapped and IM response is carefully observed. Immediately on tapping, High PIM level is observed which must ideally drop below acceptable limits after tapping. Changing IM response on each tap above the permissible limit indicates presence of PIM.

Ques:How can one localise the Internal PIM source?

Ans:The internal PIM can be localised using a PIM tester wherein IM performance with one carrier fixed and second swept can be carefully observed. In case PIM is present, IM products can be seen in the response observed on the PIM tester. The location/distance is also calculated and based on this defective component can be pin pointed.

Ques:How can one localise the External PIM source?

Ans:PIM tester can only indicate presence of external PIM. It may give indication of distance to the source of PIM. The exact localisation of source would be done using the methods used for locating External interference RF Interference Hunting