K, The efficiency of your Ethernet cable as an antenna/as a transmission line will depend on the matching of the impedance at each end of the cable. What you have done with your 22R resistor is change the matching impedance at that end of the cable as well as reducing the signal current in the cable. The characteristic impedance of the cable will most likely be about 100R. You should get the best results with both ends of the cable ideally matched as there will be no reflected signals coming back down the cable to be radiated; i.e. there will be minimal loss in the cable and hence minimal emission from the cable. However, you need to be sure to use proper Ethernet magnetics at the cable ends, which should meet the impedance requirements if installed according to the manufacturer's application note.
Best regards Neil R. Barker CEng MIET HonFSEE MIEEE Manager Quality Engineering e2v technologies (uk) ltd 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK Tel: (+44) 1245 453616 Fax: (+44) 1245 453571 Mob: (+44) 7801 723735 P Please consider the environment before printing this email. From: kbalasubraman...@scmmicro.co.in [mailto:kbalasubraman...@scmmicro.co.in] Sent: 03 May 2007 14:13 To: emc-p...@ieee.org Cc: kbalasubraman...@scmmicro.co.in Subject: Emission at SDRAM harmonics and ethernet signal current Dear Experts, In our ethernet device, by introducing series resistors of value 22 ohms in the Tx / Rx signals we noticed reduction in the emission levels. Reduction of emission in the ethernet harmonics (175, 200, 225, 250, 275, 300 & 350 MHz) is logical. At the same time we notice reduction of emission in SDRAM clock harmonics also. (multiples of 59.9 MHz). Why & how this happens and what to infer from this is not clear to us. Sincerely K.Balasubramanian Project Leader - Hardware. Sent by E2V TECHNOLOGIES PLC or a member of the E2V group of companies. A company registered in England and Wales. Company number: 04439718. Registered address: 106 Waterhouse Lane, Chelmsford, Essex, CM1 2QU, UK. - 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/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: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
