How To Avoid Electromagnetic Interference Hazards

By Alan Lowne, CEO, Saelig Company Inc.

The damaging effects of EMI

Based on a true story, the movie Lone Survivor tells the story of four Navy SEALs on an ill-fated covert mission to neutralize a high-level Afghan Taliban operative in 2005. Ambushed by enemy forces, one of the SEALs climbs to higher ground to make an emergency call via a satellite phone — not a wise move since transmissions like this are easily detected and can pinpoint a soldier’s position. Modern warfare acknowledges the vulnerability of continuous transmissions, and the technique of choice is to use bursts of short, packetized up/down data transmissions via satellite, doing subsequent information retrieval, evaluation, and creation in an electromagnetic interference (EMI)- shielded, undetectable environment.

Complex electronic systems often create unwelcome EMI/radio frequency interference (RFI), which can interfere with the operation of critical communication, computer, command, and control systems. Almost all electrical and electronic equipment can create interference or emit an electronic signature that is detectable by those of unfriendly intent. Electromagnetic energy can escape from one product and interfere with another. Signals can be radiated via an unwanted antenna extending from (or appearing in) the product — connecting leads or gaps in cases, for instance. Radio interference can be caused by sources such as electric motors, drills, poorly suppressed vehicle engines, high-power flashing lights, or nearby broadcast transmitters. Switching power supply circuits, used with many electronic products including lighting systems, are famous for contaminating the main supply voltage by adding harmonics at multiples of the 50 Hz or 60 Hz supply. These emissions can catastrophically interfere with emergency radio communication and aircraft navigation systems. This interference may not just be a radiated phenomenon, because it can also be distributed via a building’s power wiring. Powerful nearby radar installations or MRI machines in field hospitals can create unwanted interference, too, disturbing operational activity of command centers.