You'll get better results of the dimensions of the chamber are not multiples of each other, better still if their relative dimensions are prime numbers. DB
> ---------- > From: [email protected][SMTP:[email protected]] > Sent: Friday, April 30, 1999 5:13 PM > To: Aschenberg, Mat; EMC-PSTC > Subject: Re: Reverberating chambers and screen rooms > > 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" <[email protected]> > Subject: Reverberating chambers and screen rooms > Date: Fri, 30 Apr 1999 14:36:50 -0600 > To: 'emc-pstc' <[email protected]> > > > > 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 [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). > > > > > > ---------------End of Original Message----------------- > > -------------------------- > Ed Price > [email protected] > Electromagnetic Compatibility Lab > Cubic Defense Systems > San Diego, CA. USA > 619-505-2780 > 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 [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). > --------- 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).
