Ravinder
Unfortunate, but predictable (and I have come across smaller ones!) - very few small test labs can afford a properly-built and fitted out 10m chamber. As you realised, the dodgy area is the lower end of the frequency spectrum where you are more likely to be in the near field than in a bigger chamber at the same frequencies. As for the results, it has to be said that to a great extent "you get what (you can afford to!) pay for" - both in terms of facilities/equipment and of the skill and experience of the personnel performing the testing. I suppose the only way to really reconcile the use of results from a small chamber is when they show you are so far below the relevant emissions limits that even major uncertainties factors would keep you inside them! OTOH, from a "compliance perspective", all that a lot of companies want (and actually believe that they need for their compliance files) is to be able to demonstrate that their products are (or appear to be) within the relevant limits when tested in a "compliant" chamber by a nationally accredited test house - anything more is icing on the cake as far as they are concerned. John Allen Compliance With Experience Ltd. W. London, UK From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: 16 October 2012 19:44 To: [email protected] Subject: Re: [PSES] OATS vs FAR Radiated Emissions Limits Several years ago I was using a 3m FAR for pre-compliance measurements. They were using a giant BiLog antenna for the measurements. A constant factor was added to the measured values to arrive at the OATS value. The reason I stopped using their facility was because the data didn't correlate well with the 10m semi-anechoic chamber. Regards Ravinder Ajmani HGST, a Western Digital company [email protected] [email protected] Sent by: [email protected] 10/16/2012 10:25 AM To [email protected] cc Subject Re: [PSES] OATS vs FAR Radiated Emissions Limits Certainly radio frequency emissions measurement is far from an exact science, but that's probably just fine for what it is intended to do. Pass at one lab, fail at another seems to be a common theme, so there must be many variables at play. I've read that, depending on antenna size, 3 metre distance is within what is called the "near field" and if so, then I assume spectrum of radio emission wouldn't correlate well to what would be measured at 10m or 30m. ____________________________________________________________________________ ___ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: John Woodgate <[email protected]> To: [email protected] Date: 10/16/2012 09:40 AM Subject: Re: [PSES] OATS vs FAR Radiated Emissions Limits _____ In message <[email protected]>, dated Tue, 16 Oct 2012, "Pawson, James" <[email protected]> writes: >These limits are lower than those for an OATS at 3m. Does anyone know >why the limits are lower and of a different characteristic? I'm >guessing something to do with the lack of reflective ground plane in >the FAR. > In principle, an attempt has been made to reconcile the limits applicable to the different measurement environments so that products with given emission levels produce at least similar test results (dB above or, preferably, below the limit) in each environment. The deliberations that resulted in these limits were long and very complex. -- OOO - Own Opinions Only. See www.jmwa.demon.co.uk The longer it takes to make a point, the more obtuse it proves to be. 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 <[email protected]> All emc-pstc postings are archived and searchable on the web at: <http://www.ieee-pses.org/emc-pstc.html> 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/> http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: <http://www.ieee-pses.org/> http://www.ieee-pses.org/ Instructions: <http://listserv.ieee.org/request/user-guide.html> http://listserv.ieee.org/request/user-guide.html List rules: <http://www.ieee-pses.org/listrules.html> 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 email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________ - ---------------------------------------------------------------- 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://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://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://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://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://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]>
