What is Low PIM?
PIM (Passive Intermodulation) is defined as the nonlinear mixing of two or more frequencies in a passive circuit. PIM generation occurs on various orders and third order PIM distortion produces the highest level of interference.
LTE and 4G services make PIM a large concern.
With the frequency overlays and in building coverage expansion, wireless service providers are opening the door to higher and higher levels of PIM interferences. Recent developments increased the likelihood of higher than acceptable PIM levels, in most cases, LTE services are being deployed as overlays instead of converged services. The overlay of LTE services onto existing 2G and 3G services makes wireless service providers more vulnerable to the effects of PIM.
What causes PIM
Clean metal surfaces with high contact pressure generally behave in a linear manner and do not generate PIM. Where there is loose contact between metal surfaces, a non-linear relationship and the contaminated junctions causing PIM to be generated. There are a number of factors can cause PIM.
During the manufacturing process, including:
Contaminants such as solder splatters
Insufficiently thick plated metal
Scratches on the connector faces during the assembly procedure.
Ferromagnetic material plating
During the transportation process, including:
Contamination in dielectric material
Scratches on the connector faces during the transportation process
During the installation process, including:
Loose metal-to-metal contacts
Ferromagnetic materials in or near the current path
Contact between dissimilar metals
Cracks caused by over tightening the back nut during installation.
Structures or objects in close proximity to the site
During the installation environment, including:
Nearby metallic objects in the main beam and side lobes of the transmit antenna including roof flashing, vent pipes, guy wires, etc.
How to eliminate PIM
Low PIM Connectors, cable assemblies, passive components are often tested for PIM both in the design and production processes. Carefully design of the PIM system can eliminate the PIM caused by installation.
With the wireless service providers adding advanced 4G services, the complexity of the RF path is growing dramatically, each new element introduced to the system increases the chances for PIM, wireless service providers must ensure every component in the system is Low PIM.
Raynool provide Low PIM connectors, adaptors, cable assemblies, passive components tailor for Low PIM systems.
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