My understanding of the 20H rule, was with regard to planes. If the planes have noise fields between them (I don't know how this can be avoided, regardless of component/trace/via placement), when the planes end equally at the edge of the board, this makes a nice dipole antenna, and the noise radiates off the edge of the board in a nice wide pattern like you would want from a dipole. By applying the 20H rule, you distort the field between the two 'poles', and the effective radiation is greatly reduced as this is a very poor antenna. How well this applies to traces over a plane near the edge of the board, I'm not sure, but I would imagine the effect would be local, and would only be significant if there were a strong field between the two conductors (poles). -----Original Message----- From: Ian Wilson [mailto:[EMAIL PROTECTED]] Sent: Thursday, July 12, 2001 3:56 PM To: Protel EDA Forum Subject: [PEDA] 20H rule, Planes etc (Ex: perimeter stitched ground vias question) G'Day all. I have been wondering about this (the 20H rule for planes) for some time. I have been trying to think of practical situations (rather than theoretical) why there may be some advantage. First off - I agree that if both planes are equally noisy then keeping them the same extents is likely to be the best. However this may not be the case where both planes are not equally noisy. (clip) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * - or email - * mailto:[EMAIL PROTECTED]?body=leave%20proteledaforum * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Browse or Search previous postings: * http://www.mail-archive.com/[email protected] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
