In addition to Roy's article,
http://eznec.com/Amateur/Articles/Baluns.pdf

you should probably read:
http://www.yccc.org/Articles/W1HIS/C...S2006Apr06.pdf
= http://tinyurl.com/qnzs3

and also an excellent paper by K9YC:
http://audiosystemsgroup.com/RFI-Ham.pdf

The W1HIS article is written from your viewpoint, as it begins: "Your
ability to hear weak MF and HF signals is limited by noise, generated
mostly by solid-state electronic switches within your own house,
conducted via the 60-Hz power line to your shack, and from there to your
antenna by common-mode current on the feedline. Putting common-mode
chokes on your feedline, power, and other cables will substantially
reduce your received noise level."

However, W1HIS did get rather carried away with the project, and ended
up with ferrite everywhere! For the rest of us, the best advice is:
"When the problem goes away, then stop buying ferrite."



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek