Derek,
Harmonics with a 33 MHz spacing would suggest a 33 MHz clock signal, even though these are very high order harmonics. The PCI (not fast PCI) bus has a 33 MHz clock. Jim ________________________ James L. Knighten, Ph.D. Teradata, a divsion of NCR http://www.ncr.com 17095 Via del Campo San Diego, CA 92127 tel: 858-485-2537 fax: 858-485-3788 From: lfresea...@aol.com [mailto:lfresea...@aol.com] Sent: Wednesday, July 02, 2003 9:39 AM To: emc-p...@ieee.org Subject: Source of noise Morning folks.. I find myself wrestling with PC emissions again. No names this time :-) Above 500 MHz, I'm seeing a bunch of reasonably stable harmonics with about a 33 MHz spacing. Any thoughts as to what they may be from? I've played with all the case openings etc, and also added a ferrite bead to every cable leaving the MB... only minimal effect on this particular set of emissions. Ironically, the cooling fan is a big problem, it's powered from a 5 volt source that's very noisy. Consequently, the wires going to it radiate like crazy... I believe the MotherBoard is clocking around 1 GHz. Cheers, Derek N. Walton Owner L F Research EMC Design and Test Facility Poplar Grove, Illinois, USA www.lfresearch.com
