Passive Intermodulation in RF Networks and Communications: The Need for LOW PIM components.
Passive Intermodulation (PIM) functions as an interference generated by passive components, such as connectors, in the transmission lines of the cell sites. A phenomenon which, if not repaired, ends up affecting the reception of the station.
Passive Intermodulation (PIM) refers to the effect produced on transmission lines due to the nonlinear behavior that occurs at the metal-insulator-metal-MIM unions with ferromagnetic materials. This way, the PIM causes the appearance of different shades of radiofrequency (intermodulation products) from two-carrier transmission.
When 4G LTE networks are overlaid on 2G and 3G wireless network infrastructure, interference becomes a real challenge—particularly passive intermodulation (passive intermod, or PIM). PIM has been a known issue for as long as RF communications have involved more than one frequency; however, LTE is particularly sensitive to its effects.
This is a nonlinear response of two or more signals of different frequencies which are mixed in a passive device, such as for example a connector, an antenna or a splitter, among others.
This is a new challenge especially for both mobile operators as manufacturers of radio frequency components and equipment for high power transmitters and receivers at stations.
PIM: Causes that lead to this type of passive intermodulation
The causes of PIM or passive intermodulation effect are considered by experts as “complex and uncertain.” Many times bad welds and loose or dirty surfaces often lead to problems of this type.
Other times it is due to wire anchor on the site, poor quality plated on connectors, corroded or contaminated materials, as in current systems there are many more components than before for RF transmission, as can be antennas, cables or amplifiers. Therefore, each of the additional components also becomes a potential source of signal degradation.
The commitment of installers is now to constantly check the quality of these materials and components as well as analyze the diagnostic systems and test in detail the equipment in the base station. This test is particularly emphasized in the corroded components and structures, ferromagnetic metals like iron, nickel and steel, with a tendency to create hysteresis effects when RF energy is applied, irregular contact areas, spark discharges for which “hot” connections and disconnections can occur by accident, etc.
Objective: To reduce noise and ensure signal reception
The fact that radiant systems control the PIM effect allows networks to operate much more efficiently. To reduce electromagnetic noise (similar to noise) received by base station receivers allows them to “hear” better signals from the terminals.
To achieve this goal and stop intermodulation, it is recommended to follow these points:
- Increase the size of the RF components. This can decrease the current density in some areas of the system and place the sources of intermodulation generation in areas with low current densities.
- Use insulated wires, stop the use of metal and mobile contacts, as well as solder joints properly.
- Adequately select both reception and transmission bands, and prevent, as far as possible, the installation of ferromagnetic materials (steel, nickel and stainless steel and, if at all), or coating them with gold or copper
Advantages of having a low PIM
The advantages of having a low PIM and low noise level lead to improving the autonomy of the terminals (having less noise in the receiver output with less power and so the receiver can interpret the signals) and optimizes the operating costs of the network, as a base station with low PIM provides good coverage to larger areas. It also allows the sharing of infrastructure making possible that several operators share the same site to place their equipment.
This requires a number of improvements for both the owner of the network and the users, therefore it becomes very important in the mobile phone field. In fact, each time there are more and more operators who demonstrate the quality of these services since it is a determinant factor when choosing an operator
Cubitel has its own LOW PIM lab for production, testing and assembling of patchcords, cables and LOW PIM passive accesories. Contact us to define your need.