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LED RFI

Where we live, I have a very quiet noise floor and have enjoyed it for years. Recently, however, while operating on 40 meters, I noticed an offending signal on the Icom IC-7610 waterfall display. The noise repeated approximately every 15 kHz. If a CW signal happened to fall within the hash, I was unable to hear it.

I tried using the radio's noise reduction feature, which reduced the interference somewhat. However, increasing the noise reduction too much tends to distort CW signals, so that was not a satisfactory solution. I also tried the noise blanker, but it had no effect on the noise.

I began to think about what had recently changed in our home. Sure enough, my wife had recently purchased an LED light for her sewing table. As a quick test, I turned off and unplugged the new light. Immediately, 40 meters returned to its normally quiet state. When I plugged the light back in and turned it on, the offending signal returned.

The new problem.

I had several Fair-Rite Mix 31 snap-on ferrites, so I installed them on the power cord near the wall wart and  where the cord connected to the light. This made only a very small difference. The LED light's wall wart was plugged into a power bar, so I also added ferrites to the power bar's 120-volt power cord. Again, there was little improvement.

Next, I dug out my trusty battery-powered Eton radio and tuned it to a quiet spot on the AM broadcast band. Extending the antenna, I began hunting for the source of the RFI. When I moved the antenna close to the LED light's wall wart, the radio burst into noise. 

I considered trying a different power supply, but the LED light required 24 volts DC and all the spare adapters I had were 12 volts. After doing some online research, I came across a Mean Well power supply that appeared to have excellent filtering specifications. I ordered the correct model from Mouser Canada and hoped it would solve the problem.

Offending wall wart.

A few days later, it arrived. I plugged it in and—wow—the offending noise was completely gone. I placed the AM radio right beside the new Mean Well adapter and found it to be very quiet. It was satisfying to track down the source of the interference and solve the problem.

The lesson learned was simple: not all power supplies are created equal. In this case, the inexpensive wall wart supplied with the LED light was generating significant RF noise, while the replacement Mean Well supply was virtually silent on the air.

40m back to normal

The new Mean Well

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