Also, neglecting to ground the added 'dummy' plane and allowing it to float can create a mechanism to radiate EMI from (not unlike a patch antenna). From what you have told us, there is no reason to not ground it. -Ray eturkk wrote: >> <>On my home project front-panel I/O board, I initially had 1394 and >> usb2.0 differential pairs going from connector to connector on a >> _single_ layer board. The signals come from the pc motherboard with >> a cable, and on this i/o board I connect them to appropriate >> connectors. >> >> After learning the impedance requirements must be met, I ended up >> adding a dummy plane so that the fab house can control the impedance. >> >> Do I have to connect that dummy plane to ground? > > <>Stuart Brorson wrote: > <>Yes, you should connect the plane to GND. Although diff-mode currents > <>flowing on the plane will cancel each other out, common-mode currents > <>still need the GND return..... ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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