That also assumes that the tramission line has no discontinuities and both lines are perfectly length matched. This assumption is rarely true in the real world. > -----Original Message----- > From: Christman, Timothy (STP) [mailto:Timothy.Christman@xxxxxxxxxxx] > Sent: Tuesday, February 26, 2002 5:43 PM > To: 'haedge@xxxxxxxxxxxx'; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion > > > > 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 > > ------------------------------------------------------------------ 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