I never studied the statistics of what you describe, but I recall some numbers that I had for a large (50’ long x 20’ wide x 12’ high) completely bare (no anechoic material and not even a test bench) shielded chamber. I had three “stirrers”; a large 4’ x 8’ flat panel rotating about 6 RPM, a medium stirrer that had several 24” square sheets tilted at odd angles turning about 30 RPM and a shaft with IIRC three 8” corner reflectors on a single shaft turning about 60 RPM. The rotational speed was continuous, not stepped, and the rates were not synchronized nor precisely controlled. At 100 MHz, shifts in the reverberant pattern were noticeable, but not enough change was seen to make a big impression. At 1 GHz, I could see greater than 20 dB of field variation, but I needed to wait about 3 minutes before I felt enough time had elapsed to allow for all combinations to have happened. I used the chamber from 1 GHz and up, with dwell times of 3 minutes at each frequency. Over the course of that three minute exposure, there were many dips and rises, but only a few combinations actually hit the peak exposure level. For monitoring, I used a spectrum analyzer set to zero sweep width to obtain a time domain view. The trace sweep was set to about 30 seconds per division. At the end of about 4 minutes, the analyzer could display the maximum and minimum signal strength.
As I said, I didn’t think about the statistics, but it was tedious. I probably could have used several more stirring elements to shift the reverberations faster, which would have reduced the dwell time. Ed Price WB6WSN Chula Vista, CA USA From: Bill Owsley [mailto:wdows...@yahoo.com] Sent: Sunday, April 28, 2013 7:23 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Mode-stirred, Mode-tuned, Reverb - what's the difference? The debate amongst the proponents that I heard concerned the concept or idea of matching, or not , test program cycle time with paddle cycle time. The tuned folks argued that the paddle should stop at each step for a program cycle time, then there was the debate over how big is each step. At high freq's the step are necessarily small to account for the wavelength leveraged over the distance from the paddle to the EUT and what sort of variation might be expected. And the statistical study of a chamber showing variation on paddle angle per frequency. Verses the other guys that argued since the paddle rate was some speed, pick one. And the exercise program was one rate. There is just the choice of picking a rotation rate, assuming that is a controllable variable, that was some divisor or multiplier like 'pi' since it never repeats. Just stop and back up to remember what the concept of a reverb chamber was all about. If each freq or paddle positionwas to be investigated alone, why change from the previous? The intent was to increase speed and retain some degree of accuracy. _____ From: Ken Javor <ken.ja...@emccompliance.com> To: EMC-PSTC@LISTSERV.IEEE.ORG Sent: Sunday, April 28, 2013 12:34 PM Subject: Re: Mode-stirred, Mode-tuned, Reverb - what's the difference? One can mode-stir or mode-tune a reverb chamber. Mode-stirring is continuous – the paddle never ceases movement – and mode tuning utilizes a stepping movement, holding each mode for a specific time period to allow assessment of susceptibility. Can’t speak for others, but MIL-STD-461 only allows mode-tuning. Ken Javor Phone: (256) 650-5261 _____ From: Pat Lawler <pat.law...@verizon.net> Date: Sun, 28 Apr 2013 07:38:25 -0700 To: <EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Mode-stirred, Mode-tuned, Reverb - what's the difference? All, Over the years, I've come across pictures of test chambers with descriptions such as mode-stirred, mode-turned, and reverberation. They seem to look similar, with metal walls and rotating metal paddles. Do these names reference the same basic design, or are they different animals? Which ones are used for which type of RF immunity test? Thanks, Pat Lawler Teset engineer - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
