Ian,
The problem is probably a common-mode signal from some other source using the Ethernet cable as an antenna, as Ken Javor has suggested. The 20dB failure is strong evidence of that because an Ethernet signal based failure would not be that strong. Besides, 33 MHz is not a clock frequency used by 100Base-T, I don’t believe. Attacking the common-mode source on the PCB is the most effective thing to do, as others have suggested. But sometimes this is difficult. As far as STP is concerned, it will do you no good if the board-side connector (jack) is not shielded. Some are not. If the board-side receptacle is shielded, many are configured so that the jack’s shield does not make good contact to the enclosure panel. If it doesn’t, then the effectiveness of the shielding is problematic. If you don’t have a conductive enclosure to connect to, then STP may not help you much with common-mode radiation anyway. Twisted pair Ethernet can be a challenge, but the coaxial version, 10Base-2 was worse. Jim _____________________ James L. Knighten, Ph.D. Teradata, a division of NCR http://www.ncr.com 17095 Via del Campo San Diego, CA 92127 tel: 858-485-2537 fax: 858-485-3788 _____ From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org] On Behalf Of Ken Javor Sent: Friday, June 17, 2005 5:30 AM To: McBurney, Ian [Allen & Heath UK]; emc-p...@ieee.org Subject: Re: ethernet radiated emissions No experience with Ethernet per se, so this is a very general comment. It sounds as if the emissions are common mode. If so, they may not have anything to do with the Ethernet itself, the Ethernet may be a fortuitous conductor. I would check this using a current probe around the cable, with and without Ethernet traffic. If there is little or no difference, it is ground bounce in the printed circuit board driving conducted emissions onto the Ethernet. Then you have to look at suppressing emissions from that source. From: "McBurney, Ian [Allen & Heath UK]" <ian.mcbur...@allen-heath.com> List-Post: emc-pstc@listserv.ieee.org Date: Fri, 17 Jun 2005 12:17:17 +0100 To: <emc-p...@ieee.org> Subject: ethernet radiated emissions Dear colleagues; Can anyone advise me how to reduce the radiated emissions from a 100 base-T Ethernet port with a UTP cable connected to below the EN55022 class B limit? At the moment I am 20dB above the limit at 33MHz. Using STP only reduces the emissions by 6dB. Thanks in advance; Ian McBurney. Allen & Heath Limited. email: ian.mcbur...@allen-heath.com ---------------------------------------------------------------- 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 emc-p...@ieee.org Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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 emc-p...@ieee.org Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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 emc-p...@ieee.org Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
