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Re: [RFI] likely frequency for LED bulbs?

To: Greg Troxel <gdt@lexort.com>, wa4tuk <wa4tuk-rf@comcast.net>
Subject: Re: [RFI] likely frequency for LED bulbs?
From: Tom Thompson <w0ivj@tomthompson.com>
Date: Sat, 10 Jan 2015 10:43:26 -0700
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
I just made some light bulb measurements using an RF current probe, an oscilloscope, and a spectrum analyzer. My current probe is flat within 3 dB from 500 kHz to over 50 MHz. The common mode current on all bulbs was negligible through the entire HF band. The compact fluorescent and LED lamps had energy below 1 MHz but above 1 MHz the energy was down 70 dB. The LED lamp had a switching speed of about 25 kHz. There appeared to be no spectral components at the -90 dBm level between 1.8 and 30 MHz. The bulbs used were a 200 watt incandescent, a GE 26 watt helical compact fluorescent made in China, and a FEIT 60 watt replacement LED that uses 9.5 watts made in Taiwan and available at COSTCO. I can email the spectral plots to anyone interested.

73,   Tom   W0IVJ

On 1/10/2015 5:52 AM, Greg Troxel wrote:
wa4tuk <wa4tuk-rf@comcast.net> writes:

Thank you for posting your results. Information about what makes noise
and what is (relatively) quiet is hard to find. I will say I am
surprised. So far I have avoided LED lamps (A19 style) and use a mix
of incandescent and CFL where appropriate.
I was surprised when I got the first one.

I would have thought the switching rate would have been in the 100kHz
range with harmonics radiating.
Please note that I said I have other RFI sources; an attic antenna is
not a good situation to start with.  I had dealt with a number of them,
but the base level was higher than I expected yesterday.  So it's
possible that these are problematic in quieter situations.  Also, I
didn't sweep everywhere, so if there is a square wave spectrum that's
pretty limited to harmonics, I could well have missed it.

Given that these cost only $5ish these days (and that you may want to
preserve your stockpile of pre-ban bulbs :-) it seems worth buying one
or two to try out to see if you can hear them.

(Power supplies for LED strip lighting seem to be an entirely different
situation.)

73 de n1dam
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