Nearly all cell sites suffer from some degree of signal interference due to passive intermodulation, and 5G cell sites are particularly susceptible because of their high data density and greater signal integrity requirements. Effectively identifying candidate sites for PIM mitigation can help improve the long-term stability of the network. There are two main approaches to determining where to install PIM mitigation technology:
1) Universal/Preventative PIM Mitigation
Given the relatively minimal cost of conducted PIM mitigation kit installation compared to new site builds required to offset reduced capacity from PIM, carriers may wish to simply install conducted PIM mitigation kits universally across the network.
Even sites that have minimal passive intermodulation when built may develop PIM issues over time as old equipment is decommissioned, new equipment is installed, and existing equipment wears down, warps, or corrodes (i.e. the “rusty bolt effect”).
Installing PIM mitigation materials as a preventative measure minimizes site selection costs as there is no need to assess each site individually, and supports network stability for the future, as the inevitable wear and tear happens.
2) Selective PIM Mitigation
Carriers that want to focus their PIM mitigation efforts on the areas of greatest need will likely want to conduct mitigation as part of overall ongoing network maintenance. For example, if there is existing work planned at a site, it’s easy to pull a PIM mitigation kit out of the back of the van and install it in just a few minutes.
How to Select a Site for Conducted PIM Mitigation
Look for:
- Close spacing between F1 and F2 antennas. PIM mitigation kits can have a greater benefit when placed on antennas that are close together (less than 3 meters apart)
- Nonlinear elements near the antenna. Sites with mounting brackets, rusty bolts or hose clamps near the antenna are likely to be experiencing conducted PIM issues.
Avoid:
- Antennas that are positioned to directly face other carriers’ antenna arrays. Particularly at crowded sites, there may be an antenna structure in the main beam which cannot be mitigated.
- Antennas that are directly pointed at large metal objects (e.g. HVAC systems) or other nearby metal structures. Adjacent towers or light standards can also be sources of PIM which are not easily solved.
Site Hygiene Comes First
Before installing a PIM mitigation kit, it’s a good idea to make sure that many of the common sources of conducted PIM are addressed. Remove debris and unnecessary parts such as:
- Scrap metals
- Rusty bolts
- Legacy hardware (e.g. old antennas/radios). Often, this hardware is simply ripped out, leaving dangling cables or hanging brackets behind – all of which can make great “antennas” to generate PIM.
Plus, ensure that extra nuts are tightened down on bolts, and any metal parts are either in solid contact or completely isolated.
Taking these simple site hygiene steps will ensure that the kit has the best ability to mitigate overall PIM.
Questions on PIM mitigation or site selection? Contact our team to learn more about 3M PIM mitigation solutions.