I think there is a fundamental misunderstanding of the mechanism converting dm into cm, both on the part of Michel Mardiguian back in the day and those who repeat his criticism in this thread.
What people are saying, (if I understand it properly) is no different than if I used two LISNs, one with a different inductor value than the other. In that case, at frequencies where at least one LISN did not look like 50 ohms, the EMI port measurement for the dm part would be different on each LISN, and that would make it look like a cm signal, and therefore we have a problem. But that is flatly incorrect. The issue is not the relative value of the dm portion at each LISN, but rather the reference for the signal. For dm, regardless of ³balance² both dm LISN contributions sum and they are referenced from phase-to-neutral, not conductor-to-ground. As long as the dm contributions are phase-to-neutral, the bulk cap in the victim radio power supply does its job of filtering and doesn¹t care how much dm is measured to ground at each LISN. It is only when the signal is referenced to ground that the radio receiver becomes sensitized to it, because it has no line-to-ground filter elements (Y-caps). This point was made abundantly clear in the report that was presented to TC77 back in 1998 (or thereabouts). Ken Javor Phone: (256) 650-5261 From: Richard Marshall <[email protected]> Reply-To: Richard Marshall <[email protected]> Date: Sun, 3 Apr 2016 12:54:43 +0100 To: <[email protected]> Subject: Re: [PSES] Commom mode current vs. differential mode current and LISN Rich I¹m sorry! I did notice the X when it should have been Y when I received my list copy. I decided to wait to see who was alert enough to correct me. Well done and Thank you. The usual class Y value of 4,700pF presents an impedance of only 1.13 ohms at 30MHz, so it provides a very substantial unbalance to create CM from a neighbour¹s DM Richard Richard Marshall Laboratories, 30 Ox Lane, Harpenden, Herts., AL5 4HE, UK +44 (0)1582 460815 www.design-emc.co.uk <http://www.design-emc.co.uk> Member of the EMC Industry Association From: Richard Nute [mailto:[email protected]] Sent: 02 April 2016 18:24 To: [email protected] Subject: Re: [PSES] Commom mode current vs. differential mode current and LISN - A device with a single class X capacitor from neutral to ground. Safety standards require the capacitor to be Class Y. Rich - ---------------------------------------------------------------- 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 <[email protected]> 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) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- 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 <[email protected]> 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) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- 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 <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
