[Milsurplus] EMI from LED lighting

Sun Mar 9 09:26:13 EDT 2014

Group -

Couple of questions -
I have been looking on the WWW, in particular Mouser, for snap ferrite 
filter cores.   Anyone have suggestions,  I want to snap one around my 
spouses  heating pad for starters.

Would placing a toroid core/cores on the input leads to the house fuse 
box; be effective at suppressing junk coming down the line?  If so ay 
suggestions.

Thanks
Hutch

On 3/8/2014 10:05 PM, Dennis Monticelli wrote:
> No, I'm afraid not.  Sometimes I would rather deal with a limited set of
> strong tones than with a whole spread of noise, but there is no option.
>   Dithering is much cheaper than filtering or shielding so it is here to
> stay.  The motivations of publicly traded companies leave little room for
> good spectrum stewardship.  The objective is to conform to whatever the FCC
> requires and not a dB more.  We just have too many little noise makers
> these days in close proximity to sensitive receivers.  FCC Part 15 does not
> address this situation with aggressive specs, they address it with the
> standard catch-all of "must not cause interference to licensed operations
> and must accept interference from licensed operations," which is of course
> impractical given the plethora of consumer electronics.
>
> Dennis  AE6C
>
>
> On Sat, Mar 8, 2014 at 3:40 PM, J. Forster <jfor at quikus.com> wrote:
>
>> Thanks. Clever, but not exactly good stewardship. I suppose there is no
>> easy to turn off the dither.
>>
>> Best,
>>
>> -John
>>
>> ===================
>>
>>
>>> John,
>>>
>>> There are all kinds of schemes from frequency hopping to dithering.
>>> Dither
>>> is the easiest.  Dithering (i.e. FM) a PWM clock spreads it out modestly,
>>> just enough to knock down the carrier below the FCC limit while pushing
>>> the
>>> excess energy into new sidebands.
>>>
>>> Dennis
>>>
>>>
>>> On Sat, Mar 8, 2014 at 6:43 AM, J. Forster <jfor at quikus.com> wrote:
>>>
>>>> Apparently, dilution is the solution to pollution, in electronics too.
>>>> Do
>>>> you know how much they vary the frequency/period?
>>>>
>>>> -John
>>>>
>>>> ==============
>>>>
>>>>
>>>>
>>>>> My company makes IC's for electronic ballasts so I can provide a
>>>> little
>>>>> insight.  Be forewarned that the story isn't a comforting one.
>>>>>
>>>>> First of all the LED itself is as benign as an incandescent lamp.  The
>>>>> problem lies with the switching power supplies that feed a constant
>>>>> current
>>>>> from a high voltage to the low voltage of the LEDs.   All these
>>>> products
>>>>> must pass FCC Part 15.  They are not cut any slack with regard to
>>>> meeting
>>>>> the spectral mask just because they are "green" and represent a
>>>>> multi-billlion dollar industry.  Unfortunately, the FCC's spectral
>>>> mask
>>>> in
>>>>> the HF spectrum is insufficient to protect a sensitive receiver from
>>>>> noise.
>>>>>   Lights are everywhere so unless your antenna is far removed from your
>>>>> home
>>>>> and fed with well-shielded coax, you will likely experience some noise
>>>>> proportional to that proximity.  Most of the noise will emanate from
>>>> the
>>>>> AC
>>>>> line feed not the small circuit board.  So choking off the currents on
>>>> the
>>>>> AC line will help more than extra shielding around the lamp.  The IC
>>>>> makers
>>>>> are under pressure to make the chips cheap and to require minimal
>>>> external
>>>>> components for meeting EMI.  This translates into various PWM schemes
>>>> that
>>>>> smear out the noise spectrum so as to avoid high amplitude fixed
>>>> frequency
>>>>> spikes.  So instead of getting a few strong raspy tones in our radios
>>>> we
>>>>> get a general raising of the noise floor.  The total noise energy is
>>>> the
>>>>> same, just spread out.  The more consumer PWM stuff near your
>>>> antennas,
>>>>> the
>>>>> higher the noise floor becomes.
>>>>>
>>>>> I wish I had a happier story to tell.  Unfortunately, PWM devices are
>>>>> appearing everywhere in the home while the FCC is all about "let the
>>>>> market
>>>>> decide" and opening up spectrum (including your home power line) for
>>>>> various digital data formats.  The FCC doesn't really care about AM
>>>> radio
>>>>> and the next generation of consumers doesn't either. The BCB is so
>>>>> "yesterday."  Hams are just kind of caught up in the tide.
>>>>>
>>>>> Dennis AE6C
>>>>>
>>>>>
>>>>> *A friend asks:*
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> *My biggest question about LED lighting is how much radio interference
>>>>> itgenerates at frequencies up to about 30 MHz (HF).  Other users of
>>>>> theradio spectrum are more concerned by interference at higher
>>>>> frequencies,through VHF and UHF.AFAIK, an LED by itself does not
>>>> generate
>>>>> radio interference; it is theelectronics between the LEDs and the AC
>>>> power
>>>>> line that concerns me.Fluorescent lights (both CFLs and long straight
>>>>> tubes) with electronicballasts are bad because an electronic ballast
>>>>> switches AC line power withvery short rise & fall times, so the
>>>> ballast
>>>>> strongly excites the linewith radio-frequency power at whole-number
>>>>> multiples of the switchingfrequency up to 30 MHz and beyond.It is
>>>> possible
>>>>> to reduce this radio ?noise? or interference to a tolerablelevel by
>>>> means
>>>>> of shields, L-C filters, and ferrite chokes; but very fewmanufacturers
>>>> of
>>>>> fluorescent lighting products do.  If they do anything,it is nowhere
>>>> near
>>>>> enough.I?m waiting for the prices of LED-lighting products to drop
>>>> further
>>>>> beforeI buy some for evaluation.  Meanwhile, can anyone direct us to
>>>>> published,quantitative information about the radio noise generated by
>>>> LED
>>>>> lightingproducts?Best,-John*
>>>>> ______________________________________________________________
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>>>>>
>>>>
>>>>
>>
>>
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