RadioBanter - View Single Post - Ferrite noise supressors on sale at Parts Express

March 11th 05, 09:37 PM

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!