Saturday, 19 February 2011

Passive Intermodulation

Passive Intermodulation
Common Misconceptions – Sweep vs PIM:

  • Sweep tests measure efficiency of signal propagation
  • PIM tests measure ability to propagate signals without generating interference.
  • Both tests are important and necessary to ensure quality site construction 
Measurable impact on network capacity
Correcting PIM issues on a site will have a measurable impact on the RF network. Not only quality but also capacity (especially in ‘noise floor dependent technologies like W-CDMA)
Root causes of PIM:
  • Loose RF connectors
  • Poorly prepared RF cable terminations
  • Improperly mated / misaligned parts
  • Deformed / rough mating interfaces
  • Metallic debris (flakes, chips)
  • Cracked / cold solder joints
  • Loose mechanical fasteners (screws, rivets)

Quotes from operators conducting regular PIM Testing:

PIM testing helps to find RF plumbing failures that are masked or not detected during sweep testing.”
We spent extra time on every connector so you wouldn’t make us look bad.
We thought we were good before [PIM Testing]. Now, we have had to become even better.”
PIM Testing changed everything. This [PIM testing] is my report card.
You can lie to me, but you can’t lie to the PIM Tester.
Two bad [PIM] reports, they get a warning. On the third [bad PIM Report], I send them home.

  • Passive Inter-Modulation (PIM) degrades system performance.
  • Multi-band networks are susceptible to PIM internal and external to the infra-structure.
  • Multi-operator, passive DAS networks are susceptible to PIM problems.
  • Portable PIM test equipment is readily available to identify performance problems in both outdoor and indoor cellular infrastructure.
  • PIM testing and VSWR testing are necessary to verify site performance and installation quality.

No comments:

Post a Comment