[RFI] likely frequency for LED bulbs?

[Tom Thompson]

I forgot to add that the measurements that I made where  I saw energy 
were differential.

Tom   W0IVJ

On 1/10/2015 10:43 AM, Tom Thompson wrote:
> 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 at 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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>
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