Doing radiated emissions measurements using an actual antenna is of course subject to all sorts of inaccuracies due to room reflections and nulls. In our engineering mitigation efforts though, we don't use an antenna - instead we use clamp-on RF current probes on our cables. In equipment with a well-designed enclosure, the radiated emissions will all be due to (mostly common-mode) currents on cables, and we've found this method to work quite well for mitigation.
We are planning on moving that mitigation lab from an ordinary meeting room into a shielded room, basically because one is available in the building we're moving into. We will also have an anechoic chamber, so perhaps I can find the time to run some comparison tests, but in the meantime, I'm curious whether people think reflections and nulls in the shielded room will influence our current probe readings, and if so, what the extent might be and what the mechanism might be. The same question applies to LISN measurements: will we be worse off in a shielded room? Thanks for your input, Jim Eichner Sr. Regulatory Compliance Engineer Mobile Markets Xantrex Technology Inc. Email: [email protected] Website: www.xantrex.com Any opinions expressed are those of my invisible friend, who really exists. Honest. -----Original Message----- From: Jim Hulbert [mailto:[email protected]] Sent: Friday, December 15, 2000 7:09 AM To: Gorodetsky, Vitaly Cc: [email protected] Subject: Re: Shielded Room You should never use an un-lined shielded room for either radiated emissions or radiated susceptibility tests, even on a preliminary basis. The reflections of the RF signals off the walls, floor and ceiling cause errors of 20dB or more. Nulls will hide certain signals and resonances will amplify others randomly and unpredictably. You can see the strong effect of nulls and resonances by just slightly moving either the equipment you are testing or the antenna. You will never get any sort of meaningful test data. Lining the 4 walls and ceiling of the chamber with ferrite absorbing material is absolutely necessarily if you want to have any confidence at all in radiated test results. "Gorodetsky, Vitaly" <[email protected]> on 12/14/2000 03:05:38 PM Please respond to "Gorodetsky, Vitaly" <[email protected]> To: "Emc-Pstc (E-mail)" <[email protected]> cc: (bcc: Jim Hulbert/MSD/US/PBI) Subject: Shielded Room 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]> The suitability of this information for making decision is solely with the reader ------------------------------------------- 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] ------------------------------------------- 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] ------------------------------------------- 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]
