I have used and built such a room. It IS useful, An experienced engineer or technician will be able to make surprisingly accurate guesses about what a new EUT will do when outside of the shielded room. But you will have to accept that they will ONLY be guesses.
Back in the FCC Class B certification days, I assembled a room in Fort Worth about 3 by 4 meters, by splicing two old Lindgren chambers together. We also had a regular Ray-Proof 3 meter square chamber, and added a chamber about 3 by 6 meters later. (That one needed some anechoic material to be made equivalent to the others.) In each of these, we were able to test small equipment - desktop and laptop computers -- at one meter. We did so by adopting a strict 10 dB margin. This enabled us to almost always come in under the limit when we sent equipment out for the OATS tests the FCC certification process required. Some adjustment was needed in order to fine tune those results, but I look back with surprise at how well we did. The key was experience. The head of the shop there was an older engineer in his 60's who could run a 141T in his sleep - and we had one. I'd been in the Signal Corps 20 years, had been a Ham 30, and had five years experience doing FCC and TEMPEST testing myself. Later equipment upgrades allowed newer engineers to slot right in. And we had a tech who was a GENIUS at maximizing; he could add 10 dB and stay within MP4. Limitations? Sure. I would not want to test anything bigger than tabletop. Coax placement as well as EUT leads was critical. We had to strenuously avoid symmetry in the chamber; no need to excite more resonance modes that we had to. We rotated equipment by had while testing, probably mode-stirring and smoothing things out. And we learned to avoid doing certain conducted tests in the chamber, as those same resonance modes could artificially raise conducted emissions readings. Yes, you can use them. Just be very, very careful. Cheers, Cortland ====================== Original Message Follows ==================== From: "Gorodetsky, Vitaly" <[email protected]> Subject: Shielded Room List-Post: [email protected] Date: Thu, 14 Dec 2000 12:05:38 -0800 Reply-To: "Gorodetsky, Vitaly" <[email protected]> Dear Colleagues, I have been asked to comment on the scope of use/capabilities of shielded rooms (2-3m x 2m). I would appreciate if you would share your opinion on the usefulness of Radiated Emissions tests, validity of data, effectiveness of establishing an emissions baseline information of approved products for future design changes. Any recommendations for improving the usefulness? Please do not limit yourself to the above and feel free to expand. Any comments, advice will be greatly appreciated. Vitaly Gorodetsky Compliance Engineer Direct: (818) 678-3840 Canoga Perkins Corp. Main: (818) 718-6300 20600 Prairie Street FAX: (818) 678-3740 Chatsworth, CA 91311-6008 e-mail: [email protected] <mailto:[email protected]> ====================== End of Original Message ===================== ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
