[RFI] led bulb test

[Jim Brown]

On Wed,11/9/2016 9:22 AM, David Robbins wrote:
> I ran some un-reproducible tests to see if it was acceptable for use near my
> station. my basic conclusion is that it is adequately quiet, I can not hear
> anything from it on my outside antennas.  To try to find discrete signals or
> overall noise I ran a couple tests with an sdr connected to a test lead
> wrapped around the fixture and the bulb itself to find conducted signals or
> those radiated in the near field.  First, the fundamental frequency of the
> switching supply is about 85khz with a rather wide noise band up to about
> 135khz.  The wide noise band spreads out the energy of the harmonics over a
> fairly wide bandwidth so individual frequencies of harmonics can't be seen
> like a more stable source like monitors or computer clocks can.  With my
> test lead loop around the fixture (an incandescent track light) I could see
> noise about 3db above the noise floor above about 25MHz, below that I saw no
> change in the noise floor and no discrete frequencies.  I could not hear any
> increase in the noise floor with my 10m antennas aimed at the shack from
> about 200' away or on 15m from about 100' away.

Thanks for posting this work. Several comments. First, the use of an SDR 
to look at spectra of the noise is a really good idea. I'm currently 
working on updates to the ARRL Handbook, and this is something I'm 
suggesting. The SDRPlay ($130) is a particularly good choice, because it 
has a very wide tuning range and can display a large chunk of spectrum 
at one time.

Second, while this lamp is acceptable for your station with antennas 
spaced 100-200 ft from the fixture, it might not be for hams with 
antennas much closer to these lamps. Repeating your tests with closer 
spacing would be useful.  So would the SDR looking at the spectrum at 
the antenna.

Third, it would be interesting to explore the effect of the lighting 
track on radiated noise, if any. The tracks I've seen are parallel wires 
in a metallic tray that is open on one side, and the tray should be 
bonded to the green wire. Was that true for the track in which you 
tested? The SMPS is, of course, inside the base of the bulb, with 
connection only to phase and neutral.

Another great alternative for shack lighting are strips of LEDs sold by 
vendors at ham flea markets. Many of them self-regulate to a wide range 
of DC and AC voltages.Wired Communications is a good vendor who exhibits 
at Pacificon and Visalia, and has an online presence. But don't use 
their SMPS to run the lights -- use your own linear wall wart. I'm 
lighting my shack with five strips that draw a combined 1.25A from my 
12V system.

73, Jim K9YC