Hi Zhangkun, There are many ways to skin a cat. A simple approach is to reduce the diel= ectric thickness between the top layer and the next ground plane. This wil= l reduce the loop area and so radiation but also reduces the impedance of t= he trace. If you have a range of impedance that you can work with, then de= liberately reducing the impedance as above will reduce the radiation. Other= things like good stackup (all signals referenced to ground) and good high = speed design practices are always required. Good Luck! Prasad -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On= Behalf Of Zhangkun Sent: Tuesday, May 13, 2008 3:04 AM To: si-list Subject: [SI-LIST] Relativity in EMC design Hi all Currently, we have measured the radiation of signal line on external layer = of PCB. Based on the measurement result, we could gotten some design-guidel= ine for layout. For example, there is a external line of 6000mil. When the stimulus is 5mV= at 400MHz, the RE radiation at 3m is 40dbuV/m. The FCC RE limitation is 47= dbuV/m. There is remaining margin of 7db. My question is 7db is enough or not. On the PCB, there will be more than on= e line, which carry signal of 400MHz. The RE radiation maybe reinforce. How= to evaluate the relativity effect of diffrent line carrying 400MHz signal? Any advice will be helpful. Best Regards Zhangkun 2008.5.13 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu