[SADXA] LED Bulbs

[Darrel Emerson]

That's a nice article.

Over the years, I've made many measurements on LED bulbs for the house, 
but not with that precision.  Although that article measured the 
conducted emissions, as did the ARRL tests published in QST,  the 
directly radiated noise can't always be neglected. That's especially 
true at VHF.  For my worst example, I went to some trouble to put 
filtering right at the mains socket of the bulb, but that wasn't 
enough.  I had a 2-meter Yagi about 50 ft from the bulb, and even with 
the Yagi pointing in the opposite direction the RFI from the bulb raised 
the background noise at 2m by about 10 dB.  Yes, the bulb came from  
China.  I was intending to see how far I could have a QSO with the RFI 
from the bulb, but fortunately it self-destructed before I could do that 
test.

The RFI is caused by the inadequately filtered switching power supplies 
in the base of the bulbs.  I've discovered that some bulbs don't have 
any switching supply at all, but just put the right number of LEDs in 
series to reach the mains voltage, so that a simple bridge rectifier in 
the base can power them.  These bulbs produce no measurable RFI.

Cheers,

               Darrel, aa7fv.


On 7/7/2021 1:46 PM, Wes wrote:
> We are all almost forced to use them these days. But like every other 
> modern appliance they can be prodigious generators of RFI.  Here is an 
> article about measuring some of them:
>
> https://www.edn.com/comparing-conducted-emissions-from-led-lamps/
>
> Makes you want to avoid the big-box stores and by your bulbs at the 
> grocery store.
>
> Wes  N7WS
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