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Re: [RFI] Help with Bad RFI.

To: rfi@contesting.com
Subject: Re: [RFI] Help with Bad RFI.
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sat, 15 Jan 2011 09:42:25 -0800
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
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.


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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