I have a 100Base-T hub and I found that by putting
ferrite cores on EVERY line, power and data, really
quitens things down. The ferrite will stop, or reduce,
common mode emmisions which is the main noise
source. The CAT5 cables are twisted and are
transmission lines with differential RF, and don't
radiate as much, in that mode, as commonly thought.
I am also a ham, and while I don't transmit very often,
I found that my IC28 would cause the router to lock up.
The ferrite split cores stopped that problem as well.
Terry

On 11/03/2005 12:34 PM, wrote:
I have a 100Base-T hub and I found that by putting
ferrite cores on EVERY line, power and data, really
quitens things down. The ferrite will stop, or reduce,
common mode emmisions which is the main noise
source. The CAT5 cables are twisted and are
transmission lines with differential RF, and don't
radiate as much, in that mode, as commonly thought.
I am also a ham, and while I don't transmit very often,
I found that my IC28 would cause the router to lock up.
The ferrite split cores stopped that problem as well.
Terry

Interesting. Of course, the routers and NICs are supposed to use RF
chokes on the +VDC and GND lines to suppress common-mode EMI. If this
leaves some room to be desired (there are no real rules governing how
much RF choking should be done), and you are really using CAT5 (i.e.,
not CAT5E) rated cable and ends, this might explain the interference you
were picking up.

The ferrite beads will not stop the EMI at the frequencies that data is
running down the wire at. As you say, the twisted pairs wouldn't
radiate much.

Common-mode will still be a problem, and ferrite should choke that out.