The police force in Evanston, Illinois, had a problem. A mysterious transmitter was blocking the legitimate use of radios, car key fobs, cell phones, and other transmitters in an area of their town, and since it was also blocking 911 calls, they decided to investigate it. Their first call for help was to the FCC, who were not very helpful, telling them to talk to the manufacturers of the affected devices.
Eventually they approached the ARRL, the US national radio amateur organization, which sent them [Kermit Carlson, W9XA] I’m investigating. He fairly quickly identified the frequencies with the strongest interference and the likely location where it originated, and after some research it was traced to a recently replaced neon sign power supply. Surprisingly the power supply wasn’t replaced with a failsafe unit, its owner just agreed to turn it off if any further disturbance was reported.
The ARRL is highlighting this otherwise rather inconspicuous case to draw attention to the problem of devices appearing on the market with little or no claim to EMC compliance. In particular, they are critical of the FCC’s lackluster response in cases like this one. This is a serious problem worldwide, as a large number of very cheap pulse mode power supplies have replaced transformers in power applications, and in any population center its effects can easily be seen with HF radio in the form of a greatly increased RF noise floor. However we previously reported on the FCC’s investigation into the noise level issue we would tend to agree with the ARRL that effective enforcement of EMC regulations is the key to the solution.
City of Evanston police car photo, [Inventorchris] (CC BY-NC 2.0) via Flickr.
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