Each propagates undistorted, but at different velocities? Timothy J. Christman Test Engineer Tel 651.582.3141 Fax 651.582.7599 timothy.christman@xxxxxxxxxxx Guidant Corporation 4100 Hamline Ave. N. St. Paul, MN 55112 USA www.guidant.com -----Original Message----- From: David G Haedge [mailto:haedge@xxxxxxxxxxxx] Sent: Tuesday, February 26, 2002 3:56 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion Eric and all, My understanding of a transmission line that has +1 volt signal on one line and 0 volts on the other is actually the superposition of an even mode signal of +0.5 volt / +0.5volt and an odd mode signal of +0.5volt/-0.5volt, giving you the +1volt/0volt signal on the line, in which case each mode should propagate undistorted. Is this not what in fact is occurring in a line excited in this nature? David Haedge Raytheon In a nutshell, odd and even modes, and any modes in general, are special voltage patterns that propagate undistorted down a pair of transmission lines. For example, in a pair of microstrip traces, if you send a +1 v on one line and a 0v signal on the other, the actual voltage on the two lines will change, as the signals move down the line. The 0v line will see a growing negative signal as the far end cross talk builds up and the +1v signal will drop and distort as it looses energy to the quiet line. This voltage pattern is not a mode. It is just a particular driven voltage pattern. There is nothing special about it. However, there are two special voltage patterns that you can impose on the lines which will not change as the signals propagate down the lines. If you put a +1v on each line, wrt the return plane below, there will be no voltage difference between the two signal lines and the voltage pattern will continue undistorted. The other voltage pattern is a +1v and a -1v applied to the two lines, wrt the return plane. ------------------------------------------------------------------ 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: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: http://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: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: http://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