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Re: [RFI] RFI Solved After 2 Years

To: rfi@contesting.com
Subject: Re: [RFI] RFI Solved After 2 Years
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Fri, 10 Jul 2020 10:59:39 -0700
List-post: <mailto:rfi@contesting.com>
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 fixture.

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:

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:


In any of those cases the switching PS must be first discarded (smashed or burned works well).  73, Jim W6YA
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