Ed, A common mode choke is going to be your best (and maybe only) bet. I know there are filtered connectors out there – you may be able to mount one on the chassis exit point and solder on an extension to the wire that gets back to the port on the PCB. Of course that’s the crude method, but other than that, you’re likely to have issues with repeatability and reliability of the fix. This would also give a nice easy manufacturable way to attach the cable once the mods are made.
Alternatively, as others have mentioned, look for the source. Sounds like maybe switching PS noise – did the design engineers do ‘too good’ of a job bypassing the DC supply in the box and create RF current paths around/through it? I’m thinking of a product from a former job that passed easily after I selectively removed a few caps (actually, all of them) around the internal DC brick. The spec sheet for the power brick said it was Class B compliant on its own, but the design engineers decided to put some EMC caps around it anyway and created RF loops. My two cents… -Dave David Heald EMC Engineer | Worldwide Regulatory Compliance tel: +1.631.738.5373 fax: +1.631.738.5520 _____ From: [email protected] [mailto:[email protected]] On Behalf Of Price, Ed Sent: Tuesday, February 28, 2006 9:22 AM To: [email protected] Subject: Ethernet Decoupling I have a twisted-pair Ethernet receive and a twisted-pair Ethernet transmit set of 4 wires penetrating what would otherwise be a shielded box. Internal box noise, as low as 35 MHz, is getting out along this path. I put a 4700 pF feedthrough capacitor on each of the four lines. That worked pretty well, so well that the Ethernet shut down. Does anyone have a guideline about how much capacitance, L-L & L-G, that is typically OK? Thanks in advance! Ed Price [email protected] WB6WSN NARTE Certified EMC Engineer & Technician Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military & Avionics EMC Is Our Specialty ________________________________________________________________________ This email has been scanned for computer viruses. ________________________________________________________________________ This email has been scanned for computer viruses. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
