Glossary  >  Passive Intermodulation (PIM)

Passive Intermodulation (PIM)


Passive intermodulation (PIM) is a form of intermodulation distortion that arises from the action of passive elements with non-linear responses to signals. It occurs when multiple signals are present in a passive non-linear device or element.

These signals mix and multiply with each other to create other signals with characteristics similar to the original signals. But not all mixing and multiplications result in PIM.

PIM only results from specious generations of non-linearities and may be generated by everything from coaxial connectors and cables to rusty bolts and joints where different metals meet. Sometimes it even results from normally linear components.

PIM can produce interference, which can hide signals. As such, it’s necessary to remove elements that generate PIM to mitigate interference.

Instances that can rise to passive intermodulation include:

  • Connective joints where different metals meet, and oxidation occurs. This can convert the joint into an area that exhibits diode effects.
  • Coaxial connectors (especially the silver-plated kind) are susceptible to oxidation from wearing. The resulting silver oxide makes an ideal diode and causes PIM.

To prevent this, use high-quality connectors that are assembled correctly.

  • Coaxial feeder lines through their braided outer conductor, which provides many metallic interfaces that generate passive intermodulation.

To mitigate this, use a coaxial cable with good PIM performance.

  • Loose connectors and irregular contact areas can cause an inconsistent flow of current, generating non-uniform electromagnetic fields.
  • Use of ferromagnetic metals like steel, nickel, and iron, which display magnetic hysteresis when energy is applied, and a non-linear effect as a result.
  • Occurrence of spark discharges which cause craters and oxidation. This generates a diode effect and leads to poor connections.

PIM is a significant issue in the cellular industry as it can create interference within cellular communications systems that is difficult to troubleshoot. It can reduce receiver sensitivity and can even inhibit communication altogether.

Example of Passive Intermodulation in a sentence

"Detecting and resolving passive intermodulation and situations that can cause it, leads to increased reliability and performance."

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