The key that I learned, in my case, the single
pass small ferrite beads didn't suppress the RF interference
on my laptop. It took the larger (1/4" ferrites) with 3 wraps of wire through the core (you can see this is Paul's presentation, page 14). The other interesting thing, I only need the ferrites on the serial
cable running from the modem to USB adapter.
It is interesting how the high-voltage found its way into the laptop and actually caused little burns on my fingers.
Here's my earlier thread
on this subject,