Principle of ferrite beads

http://www.bytemark.com/products/ferbead.htm
http://users.catchnet.com.au/~rjandu...ts/tut_9a.html

The idea of a ferrite bead is that is is a lossy inductance. If you tried to filter out RF energy with a high Q inductor, you would get bias line resonances at certain frequencies. If you use a really poor inductor, you get signal rejection due to the inductive reactance, but you also do not get any high Q resonances since you do not get a good reflection off of the ferrite beads.