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
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