Hi Ed, This may sound like a silly question, but have you got a ground or power plane under the transformer?
Regards Doug --- "Heald, David" <[email protected]> wrote: > 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 > 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 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 __________________________________________________________ Find your next car at http://autos.yahoo.ca - 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
