Ed A typical circuit for an ethernet transformer would have 10-100nF caps between the centre-taps and digital ground on the chip side of the transformer and 1nF 2kV caps between the centre taps and chassis ground on cable side.
Any L_L/L-G caps on the cable side are going to suppress the ethernet as much as well as the noise and AIUI not permitted by 802.3. In the past I've found that one source of emission was other devices sharing the Voltage rail connected to the chip side centre taps. This was fixed by using a seperate step-down supply for the centre taps. Another option is the old favorite of ferrites on the cable..... regards Charlie > 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] <mailto:[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 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
