[RFI] flourescent light

Rick Karlquist richard at karlquist.com
Sun Nov 29 19:31:44 PST 2009

Jim Brown wrote:
> As others have correctly noted, this noise is being radiated by
> the power wiring and picked up by your antenna. The ONLY place to
> kill this noise is AT THE SOURCE, either by replacing the noise
> generator with a clean power supply or by a serious AC line filter
> right at the terminals of the noise generator. You didn't say what
> kind of lighting it is, but I'm assuming low voltage lighting with
> some sort of switching power supply that the lighting suppliers
> call an "electronic transformer."

Of course filtering at the source is best, but I have had good
luck nulling out streetlight QRM at both my city and country
QTH's by using a coaxial loop as described in my article in
the National Contest Journal, Sept/Oct 2009 (available at
Yahoo Group "Loop Antennas").  It is very well isolated from
the feedline.

Also, these streetlights tear up AM broadcast reception.  I
can completely eliminate the AM radio interference by simply
orienting my radio so as to null it.

It is a common misconception that because the power lines are
radiating, it is impossible to null out the noise.  This probably
came about because of the fact that you cannot localize the noise
by walking around with a radio with a non-directional whip.
However, despite this observation, as long as there is only
one source of RF noise, regardless of the extent of the "antenna"
connected to the source, there will be a plane of uniform phase
such that a loop in this plane will null out.  I have always
found that the loop nulls when broadside to the source of noise,
again regardless of the extent of the "antenna".

Perhaps there is a noise that cannot be nulled with a loop; I just
haven't found it yet.

Rick N6RK

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