Case study · RF line sweep
Finding a Hidden Fault on a Utility Tower
A clean-looking feedline can still be bleeding signal. On a utility-band tower in southwestern Ontario, our line sweep traced the problem to the one component nobody suspected - and proved it on the spot.
The site
A utility-owned communications tower carrying equipment on the 890-940 MHz band. The owner needed the feedline runs swept and verified - a routine health check on paper, but the kind of job where the value is in catching the thing that isn't obvious.
What we did
We swept each run end to end with an Anritsu Site Master, calibrated at the test port, across the actual operating band - Return Loss and VSWR for the overall match, and Distance-to-Fault to locate anything suspect along the run.
What we found
The Return Loss was sitting marginal - good enough to limp along, not good enough to trust. The Distance-to-Fault trace put a reflection right at 0 ft: the test port, which is exactly where the surge protector at the base of the run lives. That's a classic tell. To confirm it rather than guess, we bypassed the surge protector and re-swept.
Real BTS sweep - catching a failing surge protector
| Measurement | Pass | Marginal | Fail |
|---|---|---|---|
| VSWR | < 1.3:1 | 1.3 - 1.5:1 | > 1.5:1 |
| Return Loss | > 17.7 dB | 14.0 - 17.7 dB | < 14.0 dB |
| DTF (any point) | < 1.2:1 | 1.2 - 1.5:1 | > 1.5:1 |
The result
With the surge protector out of the path, Return Loss jumped back above spec across the band - a clear, measurable improvement that pinned the fault on a single failing component. The recommendation was simple and defensible: replace the surge protector, not chase phantom problems up the tower. The owner got clean, labelled sweep reports documenting both the fault and the fix.
Why it matters
A failing surge protector quietly degrades every watt going up that run, and it gets worse over time. Finding it took a proper sweep and the discipline to confirm the cause instead of assuming it. That's the difference between a sweep that ticks a box and one that actually protects the site.
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