Bob, In my experience in the commercial computing arena at NCR I have found that software can definitely "influence" radiated emissions.
My experience is in very high speed digital systems. In systems where the dominant EMI sources are from the I/O signals on cables, then the bit pattern of that signal has a big influence on radiated emissions. The bit pattern is determined by software, or firmware, or some set of computer instructions. For example, I have a very high speed digital system that idles with a bit pattern that is much like a repetitive clock pulse. It produces a very strong emission at its characteristic frequency. However, when the system is truly operating and sending real data, the signal bit patterns on the cables are much more complex, producing a much richer spectrum of radiated emissions, but with the peaks many dB lower than the idle pattern's peak. In this case, the software has a real influence on the emissions spectrum. I think that if you had a system that had noisier boards, so that an important EMI source were common-mode signals on the ground plane from clock signals (a common problem), then software activity may have much less effect on radiated emissions. Yes, the effects are system dependent, but for some categories of systems, software activity is an important ingredient in producing radiated emissions. I have another example! We use arrays of disk drive storage (many gigabytes) in our systems. Typically, these arrays are driven by SCSI cables. We have found over the years that we should run software programs that try to maximize disk activity (reads and writes) when performing EMI compliance tests. We usually get stronger emissions when the drives are very active. This is another example of software influencing radiated emissions. This is a bit of a ramble, but I hope the thoughts are helpful to you. Jim Dr. Jim Knighten e-mail: jlknigh...@ieee.org Senior Consulting Engineer NCR 17095 Via del Campo San Diego, CA 92127 http://www.ncr.com Tel: 619-485-2537 Fax: 619-485-3788 ---------- From: rehel...@mmm.com Sent: Monday, March 01, 1999 10:30 AM To: Knighten, Jim Cc: emc-p...@majordomo.ieee.org Subject: RE: EMC and Software Sorry for not being clear: I have received and read a fair amount of data on the containment and recovery from ESD "spikes" through the use of software. Can software also control and/or limit the amount of emissions from equipment? Harmonics? Voltage variations? I know the question is broad and the answers may be "equipment specific". But when software and hardware design engineers get together on a design, are there any general "rules of thumb" or specifics that they should be aware of in terms of EMC? Thanks again, Bob Heller ======================================================================== === =============== "Knighten, Jim" <knigh...@trans.sandiegoca.ncr.com> on 03/01/99 11:54:44 AM To: emc-p...@majordomo.ieee.org Robert E. Heller/US-Corporate/3M/US cc: Subject: RE: EMC and Software Bob, Before I respond to this, could you please elaborate a little. I am not certain I understand what you are asking for? Jim Knighten Dr. Jim Knighten e-mail: jlknigh...@ieee.org Senior Consulting Engineer NCR 17095 Via del Campo San Diego, CA 92127 http://www.ncr.com Tel: 619-485-2537 Fax: 619-485-3788 ---------- From: rehel...@mmm.com Sent: Monday, March 01, 1999 6:03 AM To: emc-p...@majordomo.ieee.org Subject: EMC and Software Could someone provide their knowledge of or resources for the control or mitigation of EMI through the use of software? Thanks, Bob Heller 3M Company --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
