[Milsurplus] EMI from LED lighting

[J. Forster]

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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