Hi,
Correlating Fully Absorber-lined Chambers to OATS (or semi anechoic chambers with a ground plane) is a complex subject. 1.) Literature If somebody wants to probe any further please consult our homepage www.euro-emc-service.de under publications (No. 117, 112, 99, 96, after 1995). Sorry, due to copy rights however we can not supply these papers, please check e.g. with a library. 2.) Technical Standards: CISPR standards presently still refer to the "ground plane situation" (CISPR 16, ANSI C63.4, CISPR 22 and 11). The physical test distance e.g. under CISPR 22 (ITE) is 10m for class A and allows 3m only for class B for radiated emissions. Many people ignore this. There is presently standardization work on "how to use FARs (fully lined)" going on in CISPR. European Standardization under CENELEC created a technical report TR EN 50147-3 (2001). I think this is the latest edition. This Doc. helps understanding physics (free space/ground plane) testing as well as correlation issues. A 5 dB limit margin for correlation is proposed. By the way EUT cables (positioning) have a very high impact on any type of radiated emission testing. I have seen anything in between 3 and 20 dB. The big schools in radiated emission testing are ground plane (compromise) or total radiated power (free space)like the GTEM cell. Assuming roughly -10 dB (even just over GPs) correlation from 3m to 10m is known to be many times leading to incorrect results. Blind angles for the various 3/10m geometries (and 1-4m height scans not covering all RE at 10m), EUT radiator characteristics (e.g. point source representation), different antenna factors in calibration (3m vs.10m, free space or over GP) and general height scan issues matter a lot. There is also the +/- 4dB NSA (normalized site attenuation, empty chamber qualification) issue. Tuned Dipoles or Broadband bicones can be used. Dipoles tend to integrate over the full half wave length, but size.... In other words using a small sensor may make the chamber look worse! Just the empty RE site has by CISPR 16 definition a measurement uncertainty of almost 6 dB. This covers so far a little bit the classical, commercial EMC area. ETSI (European Telecom Standards) offers interesting documents for free download from www.etsi.org: These Measurement Uncertainty docs compare in detail ground plane to fully absorber lined chamber performance. ETSI TR 102 273-1-1 V1.2.1 (2001-12) Introduction ETSI TR 102 273-2 V1.2.1 (2001-12) Absorber Chambers ETSI TR 102 273-3 V1.2.1 (2001-12) with GP There are many more references available. I hope these references are useful. kind regards Dr. Diethard Hansen EES President, Principal Consultant, Trainer US Senior NARTE certif. EMC Eng. 001937NE EMC+Automotive+Telecom QM+techn. EA-Auditor Euro EMC SERVICE (EES) Dr.-Ing. D. Hansen POB 64, Bahnhofstr.39, CH-8965 Berikon 2, Switzerland, Swiss VAT (Mwst.)No.:323214 tel./fax: +41 566 33 73 81 German mobile cell phone: +49(0)1736015909 www.euro-emc-service.de [email protected] (mailto:[email protected]) Consulting+Seminars+R&D-Projects Marketing+CE-Testing+ww.Audits From: [email protected] [mailto:[email protected]]On Behalf Of robert Macy Sent: Sunday, March 21, 2004 7:23 PM To: [email protected]; [email protected] Subject: Re: What is wrong in my 3 meters FAC measurement I'm impressed with how closely those two sets agree. My experience, measuring at 3m and "adjusting" the signal level for 10m is not the same as MEASURING at 10m. When the FCC changed the rules from 3m to 10m many of my clients' marginal equipment went right of compliance. Increase in signal level? Around 3.5dB In other words, there should have been a drop of 9.5 dB when moving the antenna further away. Unfortunately, the signal only dropped 6dB. - Robert - Robert A. Macy, PE .. [email protected] 408 286 3985 . . . .. . . fx 408 297 9121 AJM International Electronics Consultants 101 E San Fernando, Suite 402 San Jose, CA 95112 On Sun, 21 Mar 2004 15:25:44 +0530 [email protected] wrote: > Dear EMC Gurus, > I completed my pre-scans for an intentional > radiator (13.56 MHz) > in a 3 meters fully anechoic chamber and found that the > emission are well > within the Class B limits. The emission @ 108.48 MHz (8th > harmonic) was > around 35.8 db, @ 135.6 MHz (10th harmonic) was about 24 > db, @ 162.72 MHz > (12th harmonic) was about 29 db and @ 244.08 MHz (18th > harmonic) was about > 37.5 db. 3 samples were tested and the results were > similar for all the > 3. > But when another sample of the same model was > tested by my > counterpart in the 10 meters OATS (at USA) the results > are differing. > Emission @ 244.08 MHz is reported about 37.10 db, @ > 162.72 MHz is 31.1 db, > @ 135.6 MHz is 27.2 db and the device failed to meet > Class B limits. > The test setup is very simple and it is just the > 12 volts d.c. > output of a variable d.c power supply output connected > to the device. The > power supply used by me and by my counter part are not > same but similar. I > tried separately with a shielded cable and with an > unshielded cable and > the results were almost similar. My counterpart used only > a unshielded > cable. > Now it is great puzzle for us. What is wrong and > where? Apart from > the device being tested, the power supply and the cable > used there are no > other variables involved in the test set up. What other > factors we should > compare between both the testing? I request you all > provide your valuable > feedback. > > Sincerely > > K.Balasubramanian > Sr.Engineer, Hardware. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
