In a message dated 10/13/2003 7:17:10 AM Pacific Standard Time, leeritchey@xxxxxxxxxxxxx writes: I've tried several times to measure significant emissions from a single transmission line travelling over a plane at the distances above the plane one uses to create signal paths for logic circuits, the topic of concern in this thread, with no luck. I welcome measurements from others that supports the statement that traces over planes are significant sources of EMI. So far, no one has presented such evidence. Lacking such evidence, how can anyone make such claims? True, this thread concerns differential signals, but how are they different from single ended signals? True, Doug Brooks' paper didn't set out to measure emissions from traces on outer layers, but it did state that measured emissions were 30+ db below what a mono pole would emit. In all my measurements, the lead frames of the ICs are the big radiators. They make nice antennas. They stick up above the PCB and they have significant transient currents flowing through them, especially the power leads. Check out a PLCC with a near field probe sometime. Time for some measurements from those who want this discussion to seriously come to any conclusion. Anyone have any? Lee ************** WOW! I just got a chance to review the latest SI list inputs and I'm astounded at such comments. Lee, the "evidence" has been around for decades. The IEEE Proceedings published a special edition circa 1989 describing over 40 different surface structures on PCBs that are efficient antennas, many of which are unintentionally formed by poor trace layouts. I designed a special PCB in support of a worldwide seminar tour for Hewlett-Packard that clearly demonstrated unacceptable (i.e., >FCC Class B) radiation from single, terminated, 50-Ohm traces on a 10-inch PCB. The same board was used to demonstrate both radiation and crosstalk reductions of 6 to 14 dB by the use of guard traces between signal traces (which you recently declared as totally unnecessary). I expanded, updated, and presented both analyses and confirming measurements at multiple client companies (including IBM, Motorola, AMD, and Johns-Hopkins), and presented a paper at SuperDesignCon 95 illustrating these same effects. IBM published an excellent paper circa 1998 at a Southern California conference (don't recall which) that compared the radiation from traces as a function of their distance from the PCB edges. The bottom line is that ANY trace with current flowing on it generates EM fields and WILL radiate at some levelof efficiency. That's why one should always look to burying high-speed traces unless they are very short relative to the rise time of the signals they conduct. Surface routed differential signal traces offer opposing polarities of fields which tend to cancel, leaving only the effect of a small loop antenna to radiate (but they still do radiate). That's why I also favor tightly coupled (i.e., closely spaced) pairs for such applications (which, if I recall correctly, you also seem to dislike). Differential pairs are definitely different from individual traces. I have very little time for technical activities (what with the trout season coming to an end soon), but I could not let this thread slip by. Respectfully to all, Mike Michael L. Conn Owner/Principal Consultant Mikon Consulting *** Serving Your Needs with Technical Excellence *** ------------------------------------------------------------------ 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