A forensic investigation helped separate installation from product failure, protecting the project team and stabilizing a high-profile neutral-host DAS deployment.
Project Type
Professional Sports Venue
Los Angeles, California
System Type
Neutral Host DAS
PIM Failure Investigation and Forensic Material Defect Identification
The Challenge: Widespread PIM Failures Threatened Schedule, Cost, and System Performance
During construction of a major professional sports venue in Los Angeles, RSS was engaged to investigate an unusually high failure rate of Passive Intermodulation, or PIM, testing on newly installed ½-inch coaxial cable supporting the venue’s neutral-host DAS.
The implications were serious. Large quantities of installed cable were failing PIM, creating immediate concern around project schedule, replacement cost, and long-term RF performance. Because PIM issues can severely degrade a multi-operator DAS, the problem had to be resolved quickly and accurately before assumptions led to unnecessary rework or misplaced liability.
The core question was straightforward: were the failures being caused by installation practices, connectorization, test methodology, or defective cable material?
The RSS Approach: Eliminate Variables Before Assigning Blame
RSS approached the issue as a forensic troubleshooting exercise. Rather than assuming the installer was at fault, the objective was to systematically eliminate each possible cause until the actual failure mechanism could be proven.
This disciplined process was critical. On large DAS deployments, PIM failures are often blamed on field workmanship first. RSS needed to determine whether the problem was truly installation-related or whether a deeper material issue was affecting cable performance.
Phase 1: Verifying Installation, Connectorization, and Test Methodology
RSS began by validating the field process itself.
Cable installation methods were reviewed and confirmed to be industry-compliant. Connector installation procedures were also verified, and testing personnel were confirmed to be properly certified and using consistent methodology. To further remove doubt, multiple PIM test platforms were used, including Kaelus and Anritsu equipment, and both produced matching results. Phase-stable jumpers were also tested and performed correctly.
At that point, RSS was able to reach an important early conclusion: the failures were not being caused by poor installation, faulty connector practices, or bad test equipment.
That finding alone was significant. It prevented the project team from moving in the wrong direction and helped protect the installing contractor from being unfairly blamed for a problem that was not of their making.
Phase 2: Controlled Testing of Known-Failing Cable
With installation and testing variables largely eliminated, RSS moved into controlled field testing designed to isolate the cable itself.
Known-failing installed cable was re-terminated and then subjected to sweep testing. The electrical performance looked normal. VSWR was nominal at 1.19 or better, return loss remained within specification, and distance-to-fault testing showed no evidence of deformation or mechanical damage.
Those results confirmed two important things. First, the cable had not been physically damaged during installation. Second, the connectors were not introducing distortion that would explain the failures.
But the PIM behavior told a different story.
When the cable was touched or moved, PIM performance shifted by approximately 50 dB. That level of instability is a major red flag. It is not characteristic of a cleanly installed, mechanically stable cable assembly. Instead, it strongly indicates an internal material integrity issue.
In other words, the electrical sweep data looked acceptable, but the cable itself was unstable under real PIM conditions.
Connector Substitution Confirmed the Cable Was the Problem
To further isolate the root cause, RSS replaced the connectors with a different manufacturer.
The result did not change. The same PIM instability remained, and the same touch sensitivity was still present.
That test closed another door. Connector type was not the cause.
At this stage, the evidence was pointing away from installation and directly toward the cable material itself.
Phase 3: Statistical Sampling of New Cable Inventory
RSS then expanded the investigation to determine whether the issue was isolated or representative of a broader problem within the delivered cable inventory.
Six new spools were tested. Five passed and remained mechanically stable. One exhibited the same approximately 50 dB PIM instability seen in the failing installed cable.
That result was critical because it confirmed the issue was not limited to one isolated field condition. A percentage of the cable inventory itself appeared to be defective or compromised.
The problem was now clearly traceable to material condition, most likely tied to manufacturing, shipping, or storage damage.
What RSS Found
By the end of the investigation, RSS was able to quantify the scale of the issue.
The project included approximately 38,000 linear feet of installed cable. About 2,000 linear feet had already been replaced. Based on the failure patterns and statistical sampling, RSS estimated that roughly 6,000 linear feet of cable were defective in total, leaving an anticipated remaining replacement scope of approximately 4,000 linear feet.
That level of clarity gave the project team something they did not have before: a defensible forecast of the remaining exposure.
Root Cause: Material Defect, Not Field Workmanship
RSS concluded that the PIM failures were not caused by the installer, were not caused by connectorization, and were not caused by test equipment or inconsistent methodology.
The failures were caused by defective cable material, likely compromised during manufacturing, shipping, or storage.
That finding changed the direction of the project. Instead of chasing installation crews or reworking healthy portions of the system, the team could focus on identifying and replacing the truly affected cable.
RSS Recommendations
Based on the findings, RSS recommended a practical quality-control strategy to reduce future exposure and protect the remaining schedule.
All delivered spools should be visually inspected for physical damage before acceptance. The first 25 to 50 feet of every spool should be pre-tested before installation. Replacement efforts should then continue based on the measured statistical failure rate rather than broad assumptions or full-scale unnecessary removal.
This approach allowed the project team to move forward with precision instead of panic.
The Outcome: A Defensible Recovery Path for the DAS Deployment
RSS transformed a potentially chaotic failure event into a controlled engineering solution.
By isolating the true root cause, RSS protected the installing contractor from wrongful liability, identified the actual failure mechanism, quantified the remaining replacement scope, and helped stabilize the schedule for the DAS deployment.
Most importantly, the project team was able to make decisions based on evidence rather than assumption.
Key Takeaway
Not Every DAS Failure Is an Installation Failure
This project is a strong example of why forensic troubleshooting matters in large wireless deployments. When PIM failures begin to surface, it is easy to assume poor workmanship or connector problems. But as this venue demonstrated, the true issue can be hidden deeper in the material itself.
For owners, operators, contractors, and DAS stakeholders, the lesson is clear: before assigning blame or committing to large-scale rework, the system must be tested in a disciplined, evidence-based way.
RSS helps project teams identify the true cause of DAS performance failures, protect project schedules, and make technically sound decisions that reduce unnecessary cost and risk.
