We discuss the issue of PIM distortion and the test equipment TMG uses to combat it.
Passive Intermodulation (PIM) Distortion: What You Need to Know
Passive Intermodulation or PIM distortion is a type of distortion caused by passive, non-linear components in wireless systems. Passive components are any components that do not need electrical power and can include cables, couplers, coaxial connectors, drivers, and any joints where dissimilar metals are found together. The interference caused by PIM can obscure the intended signal. When PIM occurs, the components causing the interference generally to have to be located and removed or fixed. In this article, we look at why PIM causes issues and TMG’s testing solutions.
What Is the Challenge Posed by PIM?
The diode components of a wireless system are designed to work in a linear fashion. When oxidation or other faults cause damage to components such as switches and connectors, those components may begin to generate non-linear signals that multiply within the operational band, making it difficult to isolate the intended signal.
Environmental factors often contribute to PIM. Air pollution, very high or low temperatures, and excessive vibration can result in loose or corroded bolts and other imperfections in system components. This often happens in high power transmission towers, where oxidation causes non-linear junctions leading to passive modulation. For this reason, PIM is sometimes referred to as ‘the rusty bolt effect’.
PIM will eventually lower the capacity and reliability of the affected system, resulting in dropped calls and decreased system capacity.
Common Causes of PIM
Some of the most common culprits in cases of PIM are:
- Joints between two dissimilar types of metals and resulting oxidation
- Loose connections and irregular contact surfaces – on a macro- or microscopic level, can result in inconsistencies in the flow of current and electromagnetic fields
- Dirty connections due to environmental factors that cause the connections to deteriorate
- Oxidising coaxial connectors – especially common in the case of silver plated connectors, which weather and age. Higher quality connections will last longer without creating interference, but some deterioration will inevitably occur as the connections age.
- Feeder lines – with feeder lines, there are many metallic surfaces in the braided outer layer that have a tendency to generate passive intermodulation.
TMG’s Solution: the Kaelus IPA Series PIM Tester
TMG uses specialised PIM testing units manufactured by Kaelus to test for PIM interference. It was Kaelus that created the first PIM testing analyser unit back in 1996, and 25 years later they are still industry leaders in the field.
The IPA series PIM tester is a battery powered test analyser that can support a variety of test scenarios including testing from the top or base of the tower, from roof-tops and inside the building. The 20W device can be operated remotely using a WiFi enabled device such as a phone, laptop, or tablet, making for convenient, hands-free operation. The IPA Series PIM tester is also available with an intuitive, touch-screen interface to quickly perform tests and generate accurate reports. This is the most popular testing analyser on the market, and Kaelus also offers PIM training and certification courses for operators.
Contact TMG Today
TMG has been providing Australia’s data and telecommunications industries with cutting edge network test equipment for over 30 years. To speak to one of our friendly, experienced team members today, head to the contact section of our website.
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