At 04:21 PM 4/27/99 GMT, you wrote: >My company is planning to purchase a screen room for radiated emissions >precompliance testing. > >I'm aware that reflections can cause resonances and drastically influence >readings. What kind of testing could I do to characterize the room (aside from >simple experience)? > The simple answer would be this: don't even try. You're much better off using the company parking lot to do pre-compliance radiated emissions testing. For conducted emissions/immunity, and to a certain extent radiated immunity, a shielded room is great. But not for RE.
The reason for this is the reflections/resonances you get from the walls and the ceiling. You can get higher than 20 dB ripples on your measurements in an untreated (no absorber materials on walls/ceiling) shielded room. And these ripples are not very repeatable, they will change considerably with position (eg, moving your antenna or EUT less than an inch may result in field variations of much more than 10 dB). Because of these huge variations, testing cannot help you characterize your room and take these reflections into account in your emissions measurements. If you absolutely need to use a shielded room, try lining it with absorber materials. Even a few absorbers are better than none at all. Or try using another type of pre-compliance device like a GTEM or something similar. Another alternative would be to turn the shielded room into a mode-stir chamber. By rotating the properly designed mode stirrer, you will even out the variations which will result in fairly usable, repeatable numbers. The size of the room determines the usable frequency range. Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: [email protected] URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
