RF interference

[Martin Czech]

We have to decide:

1. differential mode interference. I.e. hot has some rf signal relative to
neutral. Easy to fix, just a rc network with a good cap should do it.
A ferrite bead over the hot line will even be better.

2. common mode. This is ugly, hot and neutral together carry the interference,
no relative voltage between them. In this case a filter will not work.
Only way: ferrite cores. You snap them ovre the cable or even wind the cable
on a core. Both, hot and neutral are together in the same direction.
This will work like a transformer, but the idea is to eat up the rf
energy in the special core material, it's lossy.

In most of the cases you have a mixture of both. This all works only
for out of band noise, rf interference in your own signal band:
no way. 

->more signal power
->shielding
->find the source of rf

m.c.