Jim Last year I started looking into this for my OATS as well but was primarily looking at the upcoming changes to ANSI C63.4 [absorber with > 20 dB attenuation over 1 GHz over freq range]. New version of ANSI C63.4 will require 2.4m*2.4m square for 3m OATS and proportionally higher for larger distances [about 8m*8m for 10m site..] I found two that meet the requirement, although I am sure there are more out there TDK Model IS-30A ETS Lindgren Model EHP-12PCL Both have distinct pros and cons. The TDK seems like it would be better for anchoring down and leaving on OATS due to closed cell absorber blended with polyethylene which should be fairly impervious to elements [at least that is the theory] The ETS comes in larger pieces and easier for transport but may not be as resistant to elements. Of course price comes into play as well.... I have done some experiments and found that NSA below 1 GHz seems to be OK on 3m site except for 1-2 sites that are out. Could have been operator error as we were doing yearly NSA tests and just stuck the absorber out there to get general idea what would happen. No time to investigate anomaly yet... Am cautiously optimistic that NSA may be OK with absorber on ground plane, which seems counter intuitive to me because I thought that the ground bounce was included in the equation for ideal site attenuation. This doesn't seem to be the case for my 10m sites which are off axis from the 3m site and we have dual masts for doing primarily Part 90 tests [TX], which won't require absorber and TIA 603 will actually point to old ANSI standard which doesn't have it. There seems to be an edge effect in VPOL if I leave the 3m foam down when I do my site attenuation for my 10m sites. Need more investigation. Using the ANSI C63.5:2006 AFs for NSA may help as well - need to do comparisons. My hope is that my OATS with the absorber will meet the CISPR 16 [site requirements as well. May need some turntable treatment but hopefully not as much of an issue as trying to meet it in a chamber from what I have been hearing. Anyway - more info than you probably needed but though I would share with you and the rest of the group [especially since you have an OATS]. Hope this helps [at least point towards some potential absorber!] Best regards, Mac Elliott [ ] Motorola Confidential Restricted (MCR), [ X ] Motorola Internal Use Only [ ] General Public
________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Knighten, Jim L Sent: Friday, April 10, 2009 1:57 PM To: [email protected] Subject: any recommendations on floor absorber? I am looking for advice as I prepare for radiated emissions testing above 1 GHz according to the CISPR test method, which becomes mandatory in 2010. I have an OATS with an all weather fiberglass dome (with a 4m diameter turntable) in which I test ensembles of floor-standing racks of equipment (each rack ~6 ft high, 2000 lbs.) Does anyone have recommendations to share with me as to candidate absorber materials for placement on the floor to meet the CISPR 16-2-3 measurement method for measuring radiated emissions above 1 GHz? I am guessing that important characteristics for absorbers may be: fragility or durability, absorption frequency range, cost, and size. I cannot easily raise my EUT to a height off the floor to clear the absorbers, not can I configure my EUT to place certain chassis higher or lower in the rack. I appreciate your help in advance. Jim __________________________ James L. Knighten, Ph.D. EMC Engineer Teradata Corporation 17095 Via Del Campo San Diego, CA 92127 858-485-2537 – phone 858-485-3788 – fax (unattended) - 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]> - 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]>
