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: ed.pr...@cubic.com[SMTP:ed.pr...@cubic.com]
> 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"
> Subject: Reverberating chambers and screen rooms
> Date: Fri, 30 Apr 1999 14:36:50 -0600
> To: 'emc-pstc'
>
>
> > 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
> >
> >
> > -
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> >
> >
>
> ---End of Original Message-
>
> --
> Ed Price
> ed.pr...@cubic.com
> 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
> --
>
>
>
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