Stretch-Wire Lighting Interference

Have spent some effort this week replacing a number of halogen spotlights with low power LED bulbs. After trialling a few different types of bulbs and replacing 12V AC transformers with 12V DC power supplies I’m (finally) really pleased with the result – a pleasant, versatile lighting scheme using only 1/10th of the power of the halogen bulbs.


During the week I also noticed a high level of broadband noise appear on my USB SDR dongle I’m running in the loft. It made sense that this might be linked with the changes in lighting. Initially the interference appeared to cycle over a period of a few seconds. That was quickly traced to the two transformers running a pair of 12V stretch-wire lighting rails across our dining room. Although the transformers were running the new LED bulbs, the slow cyclic nature of the interference suggested the transformers weren’t happy with the very low load presented so I’m quite thankful for it!

I’ve now replaced the transformers with 12V DC power supplies specifically for LED lighting. It hasn’t cured the interference (it’s now constant when these lights are on!) but at least I’m happy the new lighting is working correctly and I can control this source of interference so I can live with that. The loft SDR receiver is still a new toy and I suspect I had this interference from the wires when they were running the old halogen bulbs, I just hadn’t been looking at the radio while they were on. Here’s a screenshot of the lighting wires wiping out the VHF aeronautical band, the waterfall shows lights off (bottom), one rail on (middle), both rails on (top):

LED light interference

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