[time-nuts] EMI from florescent lights
pvince at theiet.org
Fri Aug 10 03:41:34 EDT 2007
I can't quote any quantitive data, but these bulbs are certainly
notorious for their RF noise. There have been some articles in
"RadCom" - the journal of the Radio Society of Great Britain - but I
can't find anything on their website (http://www.rsgb.org/). A
recent article had graphs showing that modern bulbs from reputable
manufacturers (like Philips) has significantly lower noise output
than those available from discount stores. I have some of the
cheaper variety (bought on offer from my local electricity supply
authority), and they give out a "digital" looking spectrum - roughly
square, and a couple of kilohertz wide, around 45KHz, and again at
90KHz (and beyond), and certainly loud enough to drown out the LF
time-signals. If you are serious about WWVB, I'd recommend a
magnetic loop antenna which a) isn't sensitive to the electric field
from the bulbs, and b) can be steered to null it it out. Lots of
designs on the web for home-made loops, or go to (for example)
Wellbrook in the UK (http://www.wellbrook.uk.com/) for a nicely made
one at about $360 (+ p+p).
Peter Vince (G8ZZR, London, England)
>A bulb in a ceiling fixture just burned out. Time to get out the ladder...
>Does anybody know how much garbage comes from the standard CFL "60 watt"
>replacements for incandescent lamps? I'm interested in both WWVB and GPS.
>WWVB is 60 KHz which is the 500th harmonic of 120 Hz. 500 is a big number,
>so maybe that's not a serious problem. I don't have any WWVB gear right now
>so this part is just academic curiosity.
>On the other hand, that fixture is only 6-8 ft from a couple of GPS antennas.
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