Jim,
Chris is correct, it is the 3rd harmonic of the 125MHz. It is coming from the RJ45 connector. Using shielded cables will help. Proper layout is the fix, the transformer has the straddle signal ground and chassis ground planes. These planes should never overlap. Another trick I found is to stitch a 2kV/0.001micro farad SMD capacitor across sig gnd and chassis gnd. This trick even works with optical interfaces. This is usually a problem when the Ethernet ports are on plug in cards as the gnd plane is not continuous which disrupts the sig return path. I can get you the part number for the cap I use if you are interested. For me it was like finding the holy grail. Ryan Jazz Jayasinghe Compliance Engineer x1198 Canoga Perkins Direct:(818) 678-3898 20600 Prairie Street Company:(818) 718-6300 Chatsworth, CA 91311-6008 e-mail: [email protected] www.canoga.com <http://www.canoga.com/> FAX:(818) 678-3798 ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Chris Wells Sent: Monday, November 24, 2008 11:09 AM To: Grasso, Charles; Knighten, Jim L; [email protected] Subject: Re: 375MHz from 10/100Base-T Jim - Interesting topic! Have you looked into the various sub circuits? Does the hardware have separate MAC and Net Phys? (common configuration) If yes then what is the interface? Plain vanila MII or ?? see link and the see also at the bottom... http://en.wikipedia.org/wiki/Media_Independent_Interface There are quite a few variations with different clock frequencies inbetween. Common would be 2.5/25/50/125 MHz clocks Unlikely to be the 15th harmonic of 25MHz from an MII but perhaps the 3rd harmonic of a GMII interface. Chris Hi Jim – Yes that is a typical Ethernet frequency! BTW I’d be interested in the fix! ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Knighten, Jim L Sent: Friday, November 21, 2008 2:17 PM To: [email protected] Subject: 375MHz from 10/100Base-T I am experiencing a robust radiated emission at 375 MHz from a rack containing various computing hardware. This seems to come from Ethernet 10/100Base-T switches, cables, etc. Have others experienced this frequency with Ethernet hookups? Jim __________________________ James L. Knighten, Ph.D. EMC Engineer Teradata Corporation Jim Bacher <[email protected]> David Heald <[email protected]> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ 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]> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ 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]>
