[RFI] RFI Solved After 2 Years

Jim Brown jim at audiosystemsgroup.com
Fri Jul 10 13:59:39 EDT 2020

These are great observations. Some definitions are in order. In the 
world of electrical parts suppliers, the "electronic transformer" that 
is virtually universal today to run LV lighting is a Switch Mode Power 
Supply, which we all recognize as a noise generator. A REAL transformer 
feeding a rectifier/capacitor filter, with or without regulation, is 
called a "magnetic transformer."

In my limited experience, "electronic transformers" are small enough to 
fit in the backboxes for most lighting fixtures, but "magnetic 
transformers" are not. This is the problem I ran into in the home we 
bought in W6 15 years ago. My EU Beverage runs about 30 ft from that 
fixture, so the best I could do was chokes on the wiring.

A few years ago, I replaced the incandescent bulbs in those fixtures 
with LEDs from Wired Communications, a vendor who has for many years 
exhibited at West Coast ham events.


A linear PSU, purchased from a mainstream industrial electronics vendor, 
is mounted in the ceiling above one of the fixtures. The greatly reduced 
current requirement of the LED instruments made it practical to fit a 
suitable PSU. I no longer need to bug the XYL to turn off the bathroom 
lights when I want to use that Beverage. I don't use a dimmer on that 

Also in my limited experience, Lutron has historically made dimmers that 
are pretty quiet. At least 15 years ago, I had contact with one of their 
designers, talking about RFI. I've not used dimmed lighting, but serious 
TopBand DXer NI6T told me years ago that a specific Lutron model was 
quiet, and when I needed one for the room where I read, I bought a 
Lutron. Since I'm the only one who uses it, I have no idea how noisy it 
might be. :)

73, Jim K9YC

On 7/10/2020 10:14 AM, Jim McCook wrote:
> Frank,
> I don't have access to the Lutron dimmer model.  The electrician simply 
> stated that it's designed for dimmable LEDs.
> Perhaps you're dealing with the switching power supply for the LEDs, an 
> entirely different problem.  Do the LEDs have a separate PS or are they 
> contained within the actual light?  I have had to deal with RFI from 
> many pendant or chandelier LEDs, and even the dreaded strip LEDs, all 
> which have switching power supplies that are radiating monsters.
> For pedants and chandeliers the little PS (POS) is usually in the back 
> box.  I've had luck with installing Corcom filters between the line and 
> that PS.  For tough cases or with strip LEDs you have to go to the attic 
> to install a "magnetic" PS, readily available on Amazon.  This is just 
> one example:
> https://www.amazon.com/LEDwholesalers-Dimmable-Magnetic-Transformer-Flexible/dp/B00J1ZVKSQ/ref=sr_1_8?ie=UTF8&qid=1516573754&sr=8-8&keywords=magnetic+transformers+for+LED+lighting 
> In any of those cases the switching PS must be first discarded (smashed 
> or burned works well).  73, Jim W6YA
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