I agree with the other responses that it is unusual for Ethernet to fail CM susceptibility at such low frequencies. There is likely something wrong with either the test fixture or the design of the Ethernet interface circuit.
At one time it was allowable to use either a direct-injection CDN or an EM clamp to perform this test. If you still have this option, try performing the test both ways. Regarding the Ethernet interface circuit, your first line of defense is the common-mode capacitor(s) connected to the center taps of the Ethernet transformer windings. Your description implies that you may have a so-called “mag jack” that places all the Ethernet magnetics inside the RJ-45 housing. These offer less flexibility with the common-mode capacitor(s) on the cable side, but they usually manage to pass the test. Look carefully at what you have in the circuit to see if there are any obvious implementation errors. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) <mailto:j...@randolph-telecom.com> j...@randolph-telecom.com <http://www.randolph-telecom.com> http://www.randolph-telecom.com From: ce-test, qualified testing bv - Gert Gremmen [mailto:g.grem...@cetest.nl] Sent: Thursday, December 10, 2015 6:16 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Conducted RF injected on Ethernet cable ... fails Immunity problems with Ethernet normally are a CM-to-DM conversion problem caused by bad symmetry somewhere. (unless the interference takes place elsewhere ie before the Ethernet chips) Don’t expect much of ferrite in the frequencies below 80 Mhz. Conducted immunity is injected out of 150 Ohms CM impedance, so 10-150 ohms of ferrite added impedance may reduce current up to 6 dB only. Check the tables of ferrite CM impedance at the problem frequency. Only big ferrites might impact the result, and they are not what you want. Go for a better transformer set, and good symmetry in lay-out and termination impedances. Are the 2 middle taps of the Ethernet ferrites been terminated correctly (at both sides)? A CM choke (4/8 coils ) of 1 to 5 mH might give a solution. Regards, Ing. Gert Gremmen Approvals manager ------------------------------------------------------------------------------------ + ce marking of electrical/electronic equipment + Independent Consultancy Services + Compliance Testing and Design for CE marking according to EC-directives: - Electro Magnetic Compatibility 2004/108/EC - Electrical Safety 2006/95/EC - Medical Devices 93/42/EC - Radio & Telecommunication Terminal Equipment 99/5/EC + Improvement of Product Quality and Reliability testing + Education Web: www.cetest.nl <http://www.cetest.nl> (English) Phone : +31 10 415 24 26 ------------------------------------------------------------------- This e-mail and any attachments thereto may contain information that is confidential and/or protected by intellectual property rights and are intended for the sole use of the recipient(s) named above. Any use of the information contained herein (including, but not limited to, total or partial reproduction, communication or distribution in any form) by persons other than the designated recipient(s) is prohibited. If you have received this e-mail in error, please notify the sender either by telephone or by e-mail and delete the material from any computer. Thank you for your co-operation. From: Amund Westin [mailto:am...@westin-emission.no] Sent: Thursday 10 December 2015 10:26 To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: [PSES] Conducted RF injected on Ethernet cable ... fails I have a failure when testing Conducted RF injected (IEC/EN61000-4-6) on Ethernet cable. Lose communication in the test range 20-80MHz (10Vrms 80% AM). Possible actions: 1. Snap on ferrite inside the EUT (do not want this action) 2. The RJ45 connector on the EUT has a little PCB and ferrite beads can be mounted by cutting the traces and place the beads onto each lines. Anybody who has a positive experience, eliminate immunity failures on Ethernet by introducing ferrite beads? … or is a Common Mode Choke Array more recommended? Regards Amund - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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To post a message to the list, send your e-mail to <emc-p...@ieee.org <mailto:emc-p...@ieee.org> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org <mailto:sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> > For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> > David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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