Author
Larry Seper
Building a high-quality RF site is a challenge our customers must meet everyday. Problem sites are often referred to as chronic, under-performing or “red” sites, as in the case of those using a dashboard monitoring system. Whenever a site falls into the problem zone, noise interference and issues with passive intermodulation (PIM) and voltage standing wave ratio can put the overall success of a carrier’s system at risk.
Legacy RF paths are often one part of the site challenge. During site audits, we see a lot of non-conforming, older products that don’t meet today’s current PIM standards. There are also multiple frequencies of varying age sharing the RF path. Many times, the RF path components consist of multiple suppliers and the many “hands” of numerous installers that complicate the expected site RF performance. There can be several different manufacturers of feeder cables, jumpers, connectors, antennas, tower mounted amplifiers (TMA) and diplexers, just to mention a few. The number of combinations that you can find on a cell site is in the thousands.
Despite the myriad of problems, trouble shooting is often ignored because it’s time consuming and requires a highly skilled crew to do the review. In a lot of instances, operational expenses aren’t available to the carrier due to budgets being dedicated to capital expenses for new site builds and capacity expansion.
Over the past year, our team performed dozens of site audits, concentrating on the RF path from the OEM baseband radio to the base station antenna. We found that about 75 percent of the problems experienced at the site were interconnect issues. It is critical that all connectivity points are meeting. We see a lot of issues with correctly connecting site components and not matching individual product specification guidelines for connectors, surge arrestors, bias tees and TMAs. Even if the original installation was performed correctly, subsequent field efforts interfering with the original interconnect often result in new path performance degradation. Frequently, poorly made RF jumpers are a significant reason for performance issues as about 90 percent of installers are still using field prepared jumpers versus factory-assembled PIM tested jumpers. Water migration due to improper weather proofing is also one of the major contributors to poor performance at a site.
Further, about 20 percent of the issues we encounter at sites come from products—mostly antennas and TMAs—that fail to meet published specifications. It may be due to the age of the product, supplied before PIM specs were introduced, or it could be simply product failure. The remaining five percent of trouble areas come from various scenarios, including near-field antenna shadowing due to improperly installed mounts and by external sources of signal interference near the cell site negatively impacting antenna performance.
How do your RF sites compare? Have you run into any similar conditions?
Think about how much time and money poorly performing sites could be costing you.
