Mat: Every shielded enclosure starts out as a reverberant chamber. You then pay big bucks to coat those reflective surfaces with foam or ferrite treatments that reduce the reflections.
But you want to shift the three-dimensional peaks and nulls around the volume of the chamber. To do this, you have to vary the reflective pattern within the room. The easiest way is to get about 3 surplus gearmotors (each with different RPM). Mount the gearmotors on the floor or ceiling or a wall of the room. Each gearmotor turns a reflective "paddle". As the paddles rotate, the pattern shifts about the room. I did a room (12' high by 36' long by 24' wide) where I used one 4'x 8' (firring strips with aluminum foil) paddle turning about 6 RPM, one 12" x 18" (sheet aluminum) paddle turning about 40 RPM, and one 12" x 18" (sheet aluminum with the corners bent at odd angles) turning about 60 RPM. During immunity testing, I was able to see peak-to-null ratios of about 40 dB in the field strength above 1 GHz. The big problems with the reverberant testing method is time and frequency. You really should wait a few minutes at each test frequency to be sure that all rotational combinations have been cycled through. This really slows a frequency sweep. You usually have to reach some compromise between sweep speed and certainty of peak detection. And, the technique becomes less capable as frequency drops. In practical size enclosures, I don't think you will get much effect below maybe 200 MHz. For emission testing, I still have some problem grasping the concept of how you relate observed emissions to a specific antenna-to-EUT separation distance. Regards, Ed ------------------------ From: "Aschenberg, Mat" <matt.aschenb...@echostar.com> Subject: Reverberating chambers and screen rooms Date: Fri, 30 Apr 1999 14:36:50 -0600 To: 'emc-pstc' <emc-p...@ieee.org> > I was wondering how feasible it is to convert a screen room into a > reverberating chamber? > How useful are reverberating chambers in measuring radiated emissions? > Mat > > Mathew Aschenberg > > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to majord...@ieee.org > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to ed.pr...@cubic.com, > jim_bac...@monarch.com, ri...@sdd.hp.com, or > roger.volgst...@compaq.com (the list administrators). > > ---------------End of Original Message----------------- -------------------------- Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: emc-pstc@listserv.ieee.org Date: 04/30/1999 Time: 16:13:37 Military & Avionics EMC Services Our Specialty Also Environmental / Metrology / Reliability -------------------------- --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
