Hello! As pointed out below (and during the thread), the whole issue shows, that two devices, being measured compliant, are not automatically compliant as a system when measured together. A 'quiet' USB device connected to a 'quiet' host can pass with a poorly shielded cable. The same device with the same cable will most likely fail when connected to a 'loud' host. <insert finger pointing between manufacturer of USB device and host here> Given the number of different product/designs in domain of personal computers that can be plugged together, I cannot imagine an easy way to cope with that. Currently it is cost vs. pressure of the government agencies which establishes some kind of balance. System integrators try to cope with that by imposing lower emission limits to their suppliers. This works, but not in every case. I have seen a computer fail radiated emissions testing thanks to a printer connected to it. The physical arrangement of the I/O ports helped to build an antenna. The same printer must have passed in another configuration. The same computer passed radiated emissions testing with a different printer. Any similar experiences? Best regards, Michael Nagel Michael Nagel Senior Staff EMC Test Engineer Embedded Computing
Emerson Network Power T +49-89-9608-0 F +49-89-9608-2376 [email protected] www.emersonnetworkpower.com/embeddedcomputing Emerson Network Power - Embedded Computing GmbH, Lilienthalstr. 15, D-85579 Neubiberg/Landkreis München, Deutschland / Germany. Geschäftsführer Josef Wenzl, Amtsgericht München HRB 171431, VAT/USt.-ID: DE 127472241 ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Bill Owsley Sent: Mittwoch, 15. April 2009 15:57 To: EMC-PSTC; [email protected]; Piotr Galka Subject: Re: SV: "Quiet" Laptop "...if all devices were tested separately the number of observed problems during using them in sets will grow by zero, zero, nothing." Alas, The problems seem to grow by the cube of the permutations of geometric sum of triple integral of number of connections. <;-) The symptom that empty ports don't radiate much, nor do poorly terminated cables that are not plugged into previously mentioned ports, seems to manifest when those two parts are plugged together, thus the reason for "system" testing. - Bill Indecision may or may not be the problem. - 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.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.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]>
