On 1/18/2011 11:44 AM, dave wrote:

...
No such thing. Those isolators just keep hum away. Hum is not your
problem. You are likely hearing triac noise (dimmer buzz, halogen
torchieres, waterbed heaters, etc.) over the air. It is coming in or
power lines and RF chokes on those lines will stop it at the electrical
box. But because you have overhead mains that probably won't help
enough. You may be able to reduce it enough to get better results from
your phase canceller. I'm peabrainstorming here...

What dave was attempting to describe is common mode noise. This is
probably at least a portion of your noise, best for you to decide:

http://www.w8ji.com/common-mode_noise.htm
http://www.dxengineering.com/TechArticles.asp?ID={3F341778-BFE9-4988-AD87-142FD1E04EB2}
http://www.yccc.org/Articles/W1HIS/C...S2006Apr06.pdf
http://www.hard-core-dx.com/nordicdx...ed/balun3.html

The links and scientific/technical papers on Common Mode Noise are
simply without end. Feel free to use a search engine and find material
which is easy for you to digest ...

Regards,
JS