Some of the most common RF noisy products around the house are LED downlights. We have had reports of banks of LED lights (60+ lights) causing QRM for HF radio at distances of up to 400 metres. Plenty of retailers sell LED lights of various brands, but it is almost impossible to tell if these lamps will create QRM prior to installation. Sure, they all come with various EMC compliance logos, but can we trust them?
So, we at QRM Guru went shopping for five popular lights to road test; all different brands. We have also included a few examples of LED lights reported by hams as being amateur radio friendly.
This review was performed in December 2019. Prices and availability may vary.
THE TEST ENVIRONMENT
As usual, we have used our Test Chamber (a gutted 1981 Philips Microwave oven) and a Rigol DSA815 spectrum analyser set to scan from 1 to 100MHz at a nice slow 800ms sweep. The chamber contains its own 240V power outlet and antenna stub. The door is well screened and contains its original ferrite door seals. This ensures that the tests will not be compromised by any external signals.
THE NOISY REFERENCE LIGHT
As a starting point to any QRM tests, we return to our reference noise source, a 12 Watt down light with a very poorly filtered driver. From experience, we know this one generates a vast amount of QRM from somewhere around DC right up to 35MHz. This is despite it’s Chinese labelling of CE and FCC compliance.
While on this topic, it is worthwhile noting that it is the driver and not the light fitting which is usually the source of most QRM woes. When the small, RF noisy driver (below) is replaced with the larger one of better quality, the noise problems completely disappear.
Unsurprisingly, this is borne out by the degree of sophistication that can be seen when the covers are removed. The smaller one has a very rough and dirty Pulse-With modulation (PWM) constant-current chopper that will disrupt communications for a fair radius. The larger unit was properly designed to pass real EMC testing.
It may well have been more interesting to be able to point out nasty emissions from a product or brand, but it was a reassuring surprise to see that all five were clean enough to be regarded as amateur radio friendly. Of course, there are many other shapes and models out there, but this experiment put five common brands to the test. If you, or a neighbour, have some lights that are giving your station a hard time, you can safely recommend these five products.
If you install other products (from any manufacturers) that are amateur radio friendly, please send us an email with your findings.
If you’ve ever wondered what’s inside an LED light, check this post.
To see a complete list of LED lights that are reported as amateur radio friendly, follow this link.
QRM Guru thanks Ian, VK3BUF for conducting these tests
From time to time QRM Guru will publish articles that will endorse or recommend a particular product or supplier. This site does not seek to promote products or services for financial gain, but may feature commercially available equipment and strategies where they provide a positive advantage in the quest for interference reduction. All such recommendations are provided in good faith.