It was a Tuesday morning in September 2022. I was on-site near a new shopping plaza in suburban Chicago, doing the final RF walkthrough on a 3-node small cell deployment. The schedule was tight. We had a deadline with the tower crew.
I had my Anritsu PIM Master with me—the MW8209A. The first node passed. Clean. The second node passed. Clean. The third node? The numbers were borderline. The instrument showed a PIM reading of -155 dBc. The spec was -160 dBc or better.
The numbers said I should stop and investigate. My gut said we were already 45 minutes behind, and the crew was waiting. It's close enough, I told myself. Those are test system tolerances. So I signed off, packed up, and moved to the next site.
Three weeks later, my phone rang. It was the customer's RF lead. The third node was dropping calls at peak hours. Not constantly, but enough that the pattern was obvious. They had a drive-test report showing a 7 dB degradation in uplink sensitivity on sector 3.
I still kick myself for that day. If I'd spent 20 minutes to swap the jumper and retest, I'd have found the connector with a tiny burr from the installation. Instead, we went back to the site with a full crew, a lift, and four hours of labor. The total cost: the $590 for the re-truck, plus $2,610 in labor and lost time. $3,200—that's what that 'close enough' call cost us.
Let me clarify what that -155 dBc reading really meant. According to Anritsu's application notes on PIM testing (anritsu.com, Application Note: PIM Testing Best Practices), a margin of just 5 dB can be the difference between a stable connection and one that degrades under thermal stress or vibration. My gut told me it was test equipment variance. The data was telling me there was a real passive intermodulation source in the RF path.
Put another way: The instrument wasn't 'uncertain'—it was detecting a physical problem that hadn't yet caused a complete failure. The PIM Master was doing exactly what it was designed to do.
After that incident, I changed my process. Here's the checklist I now follow on every field PIM test. It's not revolutionary, but it's saved me from repeating that $3,200 mistake.
That's it. That's the whole list. It's basically four things that I should have been doing anyway.
I've seen this pattern many times—engineers who are more afraid of looking slow than they are of being wrong. But when I say 'many,' I do not mean just a few. I mean I've personally documented 14 similar incidents in our team's post-mortem logs over the past 18 months. We've caught 47 potential errors since implementing that pre-test checklist.
According to a 2024 survey by the Telecommunications Industry Association (TIA), poor PIM performance is cited as a root cause in approximately 18% of small cell deployment issues that require a second site visit. That's nearly one in five callbacks that could be avoided with a stricter test protocol.
PIM testing is about trust. The trust a customer puts in your work. The trust you need to have in your data. And frankly, the trust you need to place in your test equipment—if it's telling you something is wrong, it probably is.
I still use the Anritsu PIM Master. It's a solid piece of gear. But now I listen to it. The $3,200 lesson taught me that my gut was just a bias toward speed, not a source of reliable RF data.