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Re: [RFI] Testing & Comparing Compact Fluorescents?

To: rfi@contesting.com
Subject: Re: [RFI] Testing & Comparing Compact Fluorescents?
From: "Dan Zimmerman N3OX" <n3ox@n3ox.net>
Date: Wed, 31 Oct 2007 10:10:36 -0400
List-post: <mailto:rfi@contesting.com>
> P.S.  I recently bought a 4-pack of GE CFLs at Wal-Mart,
> plugged one in and listened with my Sony 2010.  Hearing an
> S9+ birdie on 1830 kHz, I immediately returned it to Wal-Mart.

Was that with the radio very near the bulb?

Well, I know you didn't get your 160m totals by letting even a whiff
of interference in anywhere near your house ;-)

I think for the slightly more casual operator, though, S9+ signal from
a CFL from near-field coupling between the bulb and a ferrite
loopstick antenna in a portable radio doesn't necessarily translate to
any detectable real world interference.

The ability of a tiny device like a CFL to radiate any generated
energy depends a lot on its ability to couple energy into something
nearby.  A compact coil of plasma is basically a very tiny, lossy loop
antenna on 160m.   The radiation resistance is probably essentially
zero compared to the losses.o

The bulb itself has almost no capacitance to the outside world,
especially on the low bands, so it will have a really hard time
coupling any common mode energy onto the power wiring.

I think the worst case scenario is fierce differential mode excitation
of the power wiring that gets turned into common mode somewhere in the
breaker box or something...

I think the problem with testing these things is that the RF
interference potential may have more to do with how your house is
wired than what bulb you buy, though I'm sure there are better and
worse ones.

I'm absolutely not defending poor EMI design in these bulbs... as
someone who's hamming in the suburbs, I understand that we really need
to fight all such poorly suppressed devices, but I'm not sure these
bulbs are going to drown us all in S9+ interference.  A tabletop
portable radio right underneath the living room lamp may be useless,
but I can't tell any difference on any band with a house full of these
bulbs on or off.  Of course, I already have a high noise floor on the
low bands, but I don't think CFL's are a major part.  I think it's
largely the 50 year old power distribution system in my neighborhood
and switching supplies in other crap consumer gear.

I think Plasma TVs are a much worse threat.  They're much larger in
terms of a wavelength, tend to be connected to several different
pieces of gear, including a cable TV line (ground loop !) , and  most
importantly, it's awfully hard to go around to all the nearest
neighbors handing out new RFI-quiet Plasma TVs that you paid for out
of your own pocket just to get some peace and quiet.  ;-)

If every single RFI-generating piece of junk in my neighborhood was
limited to a surface area of 2x10^-7 square wavelengths and was
limited to having a single differential mode connection to the rest of
the house, I'd be in heaven.

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