Chris -- The nomenclature that Mary is using is standard in transmission line theory, in which the ground plane is counted as a third conductor. Transmission line theory at a high level treats the ground plane as an additional conductor, the same as it would treat, for example, the second wire of a twisted pair as a second conductor. While each may have different capacitive, inductive, and loss effects on the system, each is nevertheless a conductor. So two wires with no ground plane, e.g. twisted pair, is called a two-conductor system, and has one mode. Likewise, a single trace over a ground plane is also called a two-conductor system, and has one mode. Two traces running over a ground plane is called a three-conductor system, and has two modes, as she correctly stated. In the general case, an (n+1)-conductor system is said to have n modes. Mary, please correct me if I have misconstrued your usage. -- Steve Chris Cheng wrote: > Here is the problem. We are confusing the classical > definition of TEM odd/even mode (which only happen > in a two line transmission line system) and the > generic SI term of odd/even mode in crosstalk > analysis. > > A three conductors TEM mode transmission line system > has three not two modes. What you are describing is > the generic SI engineering term of analyzing the > worst case impact of aggressor to the victim lines > where the aggressors are switching in the same > direction as the victim (even) or opposite (odd). > There is no TEM odd or even modes involved. You > can even extend this definition to an N line > system. The propose of such analysis is to > understand the worst case impact of a victim line > (signal degradation and propagation variation) > under the worst case impact of crosstalk. > > May be we should drop the TEM mode definition so as > not to confuse people more ? > > -----Original Message----- > From: Mary [mailto:mary@xxxxxxxxxxxx] > Sent: Tuesday, February 26, 2002 4:04 PM > To: si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion > > Don't confuse the issue by referring to what happens in an > inhomogeneous medium. I believe Mr. Haedge's point is valid. > After all, aren't there an infinite number of ways to divide > a signal on three conductors into two complete-orthogonal modes? > The even/odd mode description is convenient for many reasons. > However, I don't think there's anything magical about these > modes. They do not propagate down a transmission line > independent of one another. It's true that if you launch an > odd (or even) mode signal down a symmetric pair of traces you > will theoretically get an odd (or even) mode signal at the > termination. However, if you launch an odd and an even mode > signal at the same time, you no longer have the symmetry that > was responsible for the "single-mode" propagation. > > I don't believe it's proper to assume that the odd-mode > propagation and even-mode propagation can be analyzed > independently. Yet there is a tendency on this list to ignore > what happens to the even mode component when the "intentional" > signal is all odd mode. > > Mary > > ------------------------------------------------------------------ > 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 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 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