What I missed in this discussion are two essential topics: - far field conditions are frequency dependent. (lambda/2pi) + this means that a 3 meter chamber will tend to respond as bad a 10 meter chamber at 3 x the frequency. + ruling the close/far field issue, means that a 3 meter chamber is usable only from a certain frequency up ( let's say antenna distance is 1 meter: transition F is 50 Mhz (here +/- 3dB accuracy problem) and safe measurements may start from 100 Mhz.
- absorber lining tends to decrease in performance with frequency; below 100 MHz reflections are inevitable, bigger linings perform better at low F. Here the 3 meter chamber literally gets filled up ! More expensive absorber material and combinations of these may improve the absorption. In bigger chambers this quality may be lower due to increased reflection distances behind the EUT and behind the antenna. Wall and top reflections are comparable. In general - with today's technologies - a larger room behaves better, but with a some frequency restrictions a small room may perform satisfactorily. Regards, Gert Gremmen, (Ing) ce-test, qualified testing =============================================== Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ =============================================== >>-----Original Message----- >>From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf >>Of Cortland Richmond >>Sent: Friday, January 12, 2001 6:34 AM >>To: Tudor, Allen; ieee pstc list >>Subject: Re: Site Correlation >> >> >> >>I'd say either a comb generator, or a sweep generator but use them to >>excite a test object of the same general size as the equipment you wish to >>test. The smaller your chamber, the more it will be affected by >>the size of >>an EUT sitting in it. If you can be pretty sure what you will >>test, add its >>cables, too. >> >>And no, I'd give the same answer for both. >> >>That's my two-cents worth, anyway. >> >>Cortland >> >>====================== Original Message Follows ==================== >> >>(Headers snipped) >> >>What's the best way to correlate a pre-compliance chamber (smaller than a >>3m chamber) to a 10m anechoic chamber? Should I use a signal >>generator and >>antenna or should I use a comb generator? >> >>Would the answer be different if I were correlating the pre-compliance >>chamber to an OATS? >> >>Thanks in advance. >> >> >>Allen Tudor, Compliance Engineer >>ADC DSL Systems Inc. >>6531 Meridien Dr. >>Raleigh, NC 27616 >>phone: 919.875.3382 >>email: allen_tu...@adc.com >> >>------------------------------------------- >>This message is from the IEEE EMC Society Product Safety >>Technical Committee emc-pstc discussion list. >> >>To cancel your subscription, send mail to: >> majord...@ieee.org >>with the single line: >> unsubscribe emc-pstc >> >>For help, send mail to the list administrators: >> Jim Bacher: jim_bac...@mail.monarch.com >> Michael Garretson: pstc_ad...@garretson.org >> >>For policy questions, send mail to: >> Richard Nute: ri...@ieee.org >> >> >>
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