We are currently evaluating absorber material for our OATS, and are trying to determine how much of the ground plane we need to cover. Obviously, the entire turntable is covered, but how far, perpendicular to the antenna-EUT axis, do the absorbers need to extend on the ground plane between the turntable and the antenna? All I seem to recall reading is that absorbers are placed between the EUT and the antenna, but don't remember seeing minimum dimensions specified. Is the 2.4m x 2.4m a "rule of thumb" that seems to work or is this actually called out in one or more of the standards? Maybe I haven't read enough standards?
John D. Flavin Teradata TCP Engineering 17095 Via del Campo San Diego, CA 92127 [email protected] V: (858) 485-3874 F: (213) 337-5432 ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Elliott Mac-FME001 Sent: Tuesday, June 16, 2009 7:15 AM To: [email protected]; [email protected] Subject: RE: CISPR22:2005 + A1:2005 Hey Tim / group I don't know whether or not this would meet the CISPR requirements but may be a place to start. The proposed ANSI C63.4 revision [that I saw last year] requires meeting the CISPR 16-1-4 requirements or alternately using absorber that is at least 20 dB down for freqs over 1 GHz [not sure what the upper range is off hand]. The requirements is a 2.4m * 2.4m for 3m OATS and proportionally larger for larger sites - which for a 10m site comes out to 8m*8m - quite a large footprint. There are companies out there that state that their absorber that meets these criteria will be weather [rain and sun] resistant and should retain their electrical characteristics for 5 years or maore - but they are quite expensive - especially for a 10m site.... This company has plastic anchors that you can attach to your ground plane to keep the absorber in place. I have done some preliminary experimentation on my 3m site with the absorber and it seems that - except for a few points - NSA comes in under 1GHz with the absorber down. May even improve. Challenged my thinking on the perfect site model and NSA curves because I thought a perfect reflection was included. Was told this would be the case but needed to see it myself. I want to repeat the tests using only ANSI C63.5 2006 antenna factors and see how it works out - maybe those few troublesome spots will come in. [if I can get site time for experimentation!.]. Would like to do these tests before the Symposium hopefully. Maybe an OATS that has a significant OFA with these absorbers would meet the CISPR requirements. If the experimentation I describe above is favorable I plan to try that as a next step and will keep the forum posted . If anyone can think of reasons that the solution above could not meet the CISPR requirements would like to hear them as well. Anyway, hope this helps Best regards, Mac Elliott [ ] General Public ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Monday, June 15, 2009 7:49 PM To: [email protected] Subject: CISPR22:2005 + A1:2005 Hello Group, I have a question on the new CISPR22 ammendment that becomes effective 10-2010. It requires free space emission measurements above 1GHz. This is typically done with ferrite absorber on the chamber floor. How does one address this issue when testing on a 10 meter OATS? Are there any site modifications needed? The OATS uses a mesh (chicken wire) for the ground plane instead of solid metal panels. Please also advise if there is any new site validation requirements to do testing above 1GHz. In the past, if NSA is passing below 1GHz, the site would be valid for testing above 1GHz. Thanks, Tim Pierce TAP Engineering & Associates ________________________________ An Excellent Credit Score is 750. See Yours in Just 2 Easy Steps! <http://pr.atwola.com/promoclk/10012657 x1221322979x1201367215/aol?redir=http:/ www.freecreditreport.com/pm/default.asp ?sc=668072%26hmpgID=62%26bcd=JuneExcfooterNO62> - 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. 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