There are indeed near field test methods. They are enshrined in vehicle-based standards, such as MIL-STD-461, DEF-STAN-5941, RTCA/DO-160 and its EUROCAE equivalent, and CISPR 25 for automotive use.
In order to address the valid concerns Mr. Woodgate raises, these standards not only specify antenna-test sample separation, but also the specific type of electric field probe or antenna used in each frequency band. Ken Javor Phone: (256) 650-5261 From: <[email protected]> Date: Wed, 17 Oct 2012 06:56:03 -0500 To: <[email protected]> Subject: Re: [PSES] OATS vs FAR Radiated Emissions Limits And has any of this OATS, SAR, FAR, and TEM cell data differences been correlated to actual interference problems? Is the EMC industry crying "wolf"? Limits and test methods should be based in reality. They should not be academic exercises. For example, much of the world's products are in the near-field of each other (cockpits, OR, control rooms, etc.). Why aren't there near field test procedures? Yes, I know the problems but those are just excuses. Methods need to be developed (and alas, I'm not smart enough). Bob Heller St. Paul, MN 55107-1208 Tel: 651-778-6336 Fax: 651-778-6252 ================================= From: Cortland Richmond <[email protected]> To: [email protected] Date: 10/16/2012 02:46 PM Subject: Re: [PSES] OATS vs FAR Radiated Emissions Limits Sent by: [email protected] Around 1984 we were using a too-low 3 semi-anechoic chamber at Wang Labs to audit out outgoing shipments. Not far away, Glenn Dash was arguing that this was not nearly accurate enough. We transported a specimen equipment to Dash, Strauss and Goodhue in Boxboro, and had his people measure it, then back to our chamber and had them repeat the test. Then we used correction factors to adjust the worst case in the chamber to what was seen outside. We never got one back failing. However, that was just for audit. I DID find a few things that had been done wrongly by manufacturing, domestically and in China. Got one memorable call in the middle of *his* night from a VERY p*ssed off Chinese plant manager. Heh. Old times. Who audits now? Cortland Richmond (ka5s) On 10/16/2012 1503, John Woodgate wrote: In message <of1052898f.98b070cf-on88257a99.006668eb-88257a99.0066f...@hgst.com> <mailto:of1052898f.98b070cf-on88257a99.006668eb-88257a99.0066f...@hgst.com> , dated Tue, 16 Oct 2012, [email protected] <mailto:[email protected]> writes: 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. This sort of thing will continue, but we may hope that it doesn't create an insuperable problem, because the correct technical procedure would be to establish an empirical correlation (possibly very complex) between SAR, FAR and OATS by means of a huge 'round-robin' test of hundreds of different product samples in each environment. Clearly, no-one will pay for this. The standards-makers have done their best within the realms of the possible. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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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]>
