On 1/15/2011 7:50 AM, Tom Thompson wrote:
> I
> have had some success mitigating the noise with common mode chokes right
> at the ballasts.
Tom,
As I understand it, noise is radiated by wiring on both sides of the
ballasts, including the fixtures themselves (if, for example, they are
typical linear fluorescent fixtures). You might consider choking the
secondary (fixture side) if that is practical. I'm also told that
shielding the fixtures can help. I would expect the noise radiated on
the secondary side to emphasize the higher frequencies.
When winding the common mode chokes, pay attention to their resonance
with respect to the frequencies where you are experiencing the greatest
problems. There is measured data for several practical chokes in
http://audiosystemsgroup.com/RFI-Ham.pdf Pay special attention to the
data for a bifilar winding on a single #31 core, and try to do the
equivalent with flexible cord (all three conductors) feeding the
fixture. Also, consider a larger choke (more turns) in series with a
smaller one.
73, Jim Brown K9YC
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