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[RFI] Dealing with RFI from light dimmers

To: rfi@contesting.com
Subject: [RFI] Dealing with RFI from light dimmers
From: Frank O'Donnell <vfo@inkbox.net>
Date: Thu, 26 Dec 2019 19:48:42 -0800
List-post: <mailto:rfi@contesting.com>
I was interested in the recent posts regarding light dimmers, as this is a significant issue for me. We have three dimmers in our house, and three more in a guest house directly behind. As of yet, the brand name on all of these is unknown. Banning dimmers from these houses is not an option.

Currently I'm operating on 630m and listening across the MF/LF spectrum, where RFI from these devices seems much stronger than at HF. The strongest RFI is getting into a receiver in our main house from dimmers in the guest house, which is physically closer to the receiver's antenna but on a different power service drop. So I'm wondering if the RFI is traveling through AC wiring, or if it might be getting from the dimmers to the antenna. The shack gear's power is all filtered, through Tripp-Lite power strips and wrapping AC cords through FT240 toroids.

I noticed that one or two people here mentioned having good luck with Lutron dimmers, but others cited issues with these.

I see the ARRL RFI Book states, "The best cure is to replace the control with a better one that has a built-in RFI filter. (Beware of dimmers in plastic cases!)" It also discusses placing an AC line filter at the dimmer, as well as one or two common-mode chokes made by wrapping AC wiring around an F(T)-240 or F(T)-140 ferrite core.

Lutron has this application note on RFI and dimmers:


It mentions Lamp Debuzzing Coils (LDCs) as "the most effective way to reduce RFI."

So I'm wondering about the best things to try as next steps. Are some Lutron models more effective than others? If the RFI is originating in our guest house on a different service drop, is it likely that adding filters to the AC supply to the dimmers there would help? Has anyone had any luck with LDCs?

Thanks for any suggestions,

Frank K6FOD

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