[Milsurplus] EMI from LED lighting

[John Hutchins]

All -
    Thanks Dennis for the information.  Now who works in the Heating Pad 
area ?  Now that makes some real noise.
Hutch

On 3/8/2014 8:43 AM, J. Forster wrote:
> Apparently, dilution is the solution to pollution, in electronics too. Do
> you know how much they vary the frequency/period?
>
> -John
>
> ==============
>
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>> 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:*
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>> *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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