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.

On 10/03/2005 11:19 PM, wrote:
Good point on shielding the router. Metals boxes and wire mesh for
ventilation are easy to come by.

If I have gear to near to the computer, I can hear a click every two
seconds or so, which I suspect is due to polling on the router, or
communications between the router and the print server.

I have one of those "zap checkers" which indicates RF is being emitted,
though it does not indicate the frequency of the signal. I've seen RF
on the cat5, but haven't bothered to check the boxes.

CAT5 (not CAT5E) has much lesser near-end x-talk protection, and I
recall that it can emit EMI spikes at specific frequencies. This might
be what you are hearing. CAT5E does not have this problem, I understand.

See if the cable and routers are rated CAT5E. It might be worth the
expense to try it out on one data line to see if the noise is minimized.
Heck, it might be worth it to pull most of the cables and see if the
router makes similar noise. The noise may not be network traffic
related. Or power down the router but leave the nodes connected.

Also, another reply to this thread mentions that ferrite material did
choke out common-mode RF. It may help, especially if the router has
less than stellar RF choking on it's ethernet +VDC and GND lines.

If the router is the noisiest part, then my advice about making sure the
connectors are all in good shape still holds. I bet you could snap a
ferrite bead on the power supply/wall wart powering the router, too.

I'm still pretty sure that the twisted-pair lengths themselves are
minimal EMI radiators (or the radiation falls off sharply over
distance), but the ends can still radiate quite a bit, and common-mode
EMI is always a problem. Like most things radio all this is
half-science and half-magic. If it works for you, then it works!

My guess is the better the cable, the better the balance of the twist,
so the lower the RFI. If that were the case, then maybe going cat 6
would be the way.

Also thinking out loud, it seems with DSL you should filter the analog
signals as soon as possible, i.e. where it enters the house rather than
at the phone with those in-line filters. I'm sure the DSL on the crappy
phone twisted pair radiates a bit.