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Re: [RFI] Dealing with RFI from light dimmers

To: rfi <rfi@contesting.com>
Subject: Re: [RFI] Dealing with RFI from light dimmers
From: Rob Atkinson <ranchorobbo@gmail.com>
Date: Fri, 27 Dec 2019 11:11:35 -0600
List-post: <mailto:rfi@contesting.com>
The ideal solution is to place small variable auto transformers in
series with the lamp switches.  You can't do this as easily and safely
with outlets but if you have a switch and circuit dedicated to a
fixture such as an overhead lamp, a small variac will work _if the
circuit is never used for anything else_.   You have to cut out part
of the wall near the switch and put in a box with the variac and close
it back up.   Theaters and other venues where house lights have to be
dimmed use variacs because they don't cause filament ringing.   Your
typical cheap dimmer sold at hardware stores dim lamp filaments by
chopping off the sine wave and the control adjusts the degree of cycle
that the sine wave is off.  The sudden chop off is what causes RFI
because it is a square wave type instant on and off which generates
harmonics and makes the filament vibrate.   Variacs never cut off the
sinewave; instead they lower its peak voltage.   Nice and clean and
noise free.   The best solution, to never generate any RFI in the
first place, will be the most expensive--another example of you get
what you pay for.   But, you'll save money on incandescent lamps
because if you gradually ramp them up with the variac, the filaments
will last much longer.


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