We are having issues with a legacy leaky coax system that we suspect is experiencing multi-path interference. What are our options?

A: Problems with RF buried sensors can arise when they interact with adjacent metal objects, such as perimeter fences. Multi-path interference occurs when a signal generated by the buried cable sensor jumps to a fence, travels along it, then re-joins the static field further down the detection zone, typically generating false alarms, though there may be other issues, too.

False alarms in wired systems are usually the result of an impedance mismatch that causes signal reflection. The answer is to select perimeter solutions that reject multi-path interference generated false alarms by looking at the sensor cable signal from both directions using E2EC shielded sub-miniature sensors that can be embedded in metal.

What’s painful about measuring for multipath interference in perimeter security applications is the tiny signals involved, as well as the odd ways in which these adjacent signals may impact the primary signal, including unexplained false alarm events, voltage drop, latency, signal degradation and data packet jitter in digital systems. The situation may be more complicated if the fence is supported by security sensors that incorporate the fence structure.

Some perimeter security systems keep an eye out for signs of multi-path interference, in other cases, you’ll need to isolate the secondary path. Talk to manufacturers about solutions.

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