I would suggest that the terminology is getting in the way. I'm presuming the standard discusses any multiple or harmonic of the clock because it is the highest point likely to have any significant elements, and searching above that isn't productive or necessary. With that in mind determine which is the item under test and what is support equipment. The 5th harmonic applies to the test item, not support items, in my opinion. The test item is the USB gadget, the PC is support equipment. Presumably the support PC is - or at least once was - compliant. It would have been tested the X harmonic of its clock whether that be higher or lower than the true item under test - the USB gadget. To me that means I would only test to the 5th harmonic of the USB gadget regardless of the clock rate of the support PC as long as the USB.
-----Original Message----- From: John Woodgate [mailto:[email protected]] Sent: Thursday, September 29, 2011 8:36 AM To: [email protected] Subject: Re: [PSES] Part 15 highest test frequency for a USB PC peripheral In message <[email protected]>, dated Thu, 29 Sep 2011, Nic Johnson <[email protected]> writes: >When testing a USB PC peripheral to FCC part 15, does anyone know if >you need to go up to the 5th harmonic of the highest frequency of the >PC or just the highest frequency used in the peripheral? I can?t find >any rules that say this specifically. Does this also relate to CISPR 22/EN 55022? It seems to me that if it means the highest frequency used in the PC, you could get an optimistic result by using a very 'slow' PC and therefore you would have to use a PC with the highest possible frequency, and that is impracticable because such a beast may not be available to you, and tomorrow there could be a faster one. My conclusion is that logic dictates that it is the highest frequency used in the peripheral. But interpretations of standards are not always based on logic.(:-( -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK When I point to a star, please look at the star, not my finger. The star will be more interesting. - ---------------------------------------------------------------- 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://product-compliance.oc.ieee.org/ 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]> - ---------------------------------------------------------------- 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://product-compliance.oc.ieee.org/ 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]>
