33MHz - sounds like PCI bus. The radiation originating from Ethernet is very broadband per se as the data is scrambled using a pseudo-random code, thus widening the spectrum. This was intended to reduce EMI. There are several things to think of: - The traces between the magnetics and the connector must be short and well separate from the rest. - Keep the PWB voided of any planes/other signals in this space. - The place under the transformer should be voided as well in order to not compromise the CMR of the transformer. - ... The fact that emission decreases with STP makes me think that there is a connection between the RJ45 socket and the faceplate. SMSC had a nice application note describing ways to avoid common EMI problems with an Ethernet design. The application note is no longer on their website, but I can send it to you if you are interested. Good luck, Michael Michael Nagel Senior EMC Engineer Motorola GmbH ECC Embedded Communications Computing Lilienthalstrasse 15 85579 Neubiberg/Muenchen - Germany Ph: +49-89-9608-0 Fax: +49-89-9608-2376 e-mail: [email protected] info: http://www.motorola.com/computers
From: [email protected] [mailto:[email protected]]On Behalf Of McBurney, Ian [Allen & Heath UK] Sent: Freitag, 17. Juni 2005 13:17 To: [email protected] 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: [email protected] ---------------------------------------------------------------- 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/listserv/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: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
