What is Passive Intermodulation (PIM)?
PIM stands for Passive Intermodulation which means an unwanted signal created by the mixing of two or more RF signals, caused by the nonlinearity of the passive components in the RF path such as antennas, filters, cables or connectors. The signals will mix or multiply with each other to generate other signals that are related to the first ones. PIM can occur in a variety of areas from coaxial connectors to cables, even rusty bolts or any joint where dissimilar metals occur.
There are three primary sources for PIM:
- External interference from adjacent sites
- External interference from metal objects in nearby environments such as a fence, masts, metal joints etc.
- 50 Ohmes transmissions line to the antenna generated in your system, such as:
a) Antennas, surge protectors
b) Feeder lines, joints/jumpers
c) Diplexers, filters, couplers, tappers
d) Coaxial connectors.
There are numerous causes of Passive intermodulation. These can include:
- Mechanical considerations
- Metallic contact
- Electron Tunnelling Effects
- Fritting (Micro Arcing)
- Ferromagnetic materials such as iron, nickel, and some alloys of magnesium, aluminium and copper are ferromagnetic.
- Ferrimagnetic materials including ferrites used in isolators, circulators and phase shifters.
- Dirty connections which are not weatherproof
- Loose connections and irregular contact areas
- Poor quality plating
IEC 62037 is the standard for measuring PIM in passive components such as connectors, cables, cable assemblies and components. There are several parts to this standard for measuring PIM in various components such as filters and antennas (more details can be found at (www.iec.ch).
PIM has some severe effects on radio communication leading to;
- Higher Bit Error Rate (BER)
- Data Connection (More error protection bits are created and resent leading to a lower overall data rate)
- Reduces sensitivity leading to lower coverage
- More drop out calls
- Blockage of a receiver.
No matter what you do, PIM will always be there. Any linear device has a non-linear factor /contribution that causes PIM. However, there are several ways you can deal with PIM:
- Minimise the number of junctions in a system
- Solder junctions if possible
- Plating for all RF contact to prevent oxidation
- Sufficient thick plating for RF contacts
- Tighten connectors with recommended torque
- Take care of good sealing for connector and cable assemblies.
So what does antennaPRO supply? Amphenol Procom is introducing a series of low PIM product including broadband tappers, broadband high power splitters, broadband diplexers, broadband couplers, loads, attenuators, multiband combiners, indoor antenna, colinear antenna, panel antennas. For more information, contact our sales team on 01227 743099 or email email@example.com