Re: [PSES] Puzzle

[Doug Powell]

All, John's comment about "improved", devices prompted a thought. Often these so called improvements involve making devices faster and more efficient. This speed increase has to do with reverse recovery times of diodes and storage time of switching transistors (slew rates).  The reciprocal of 200 MHz is 9 nS; very fast. Most power switching devices produce odd harmonics from the fundamental of the pulse frequency.  However, fast slewing edges can produce both even and odd harmonics.  Look for components used in the switching power supply or data drivers with high current drive with edge times of 9, 18, 27, 36, or 45 nS; approximately.  Some MOS FET clock drivers can produce a few amps of high frequency circulating current. If the power supply turns out to be the problem AND it is not part of the product evaluation, replace it with a linear lab quality power supply or batteries. Alternatively, I've heard it said you can "clean up" a switch mode power source with a minimum of 7 stages of alternating common mode and differential mode EMI filters.   Thanks, - doug Douglas Powell http://www.linkedin.com/in/dougp0 Sent from my BlackBerry 10 smartphone on the Verizon Wireless 4G LTE network. From: John Woodgate Sent: Saturday, December 7, 2013 12:01 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Reply To: John Woodgate Subject: Re: [PSES] Puzzle In message <8d0c177fd8029e2-16d0-1d...@webmailstg-m04.sysops.aol.com>, dated Sat, 7 Dec 2013, Derek Walton <lfresea...@aol.com> writes: >In the meantime, can anyone make suggestions about what may cause this >noise, besides parasitic oscillations/faulty parts, and what radiating >mechanisms can be uninfluenced with the protection measures I took. You **seem** to have covered all the angles, but we must conclude that you haven't. Are you QUITE sure about the absence of ambient? Will the chip makers proudly confirm that they 'improved' on or more of the devices? Did you try another spectrum analyser? -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com>