The large size you mention rings a faint bell of memory... There was some caution about using a chamber at frequencies above its first resonance which is based on size.
The peaks and nulls of the multi-modal chamber then skew the reverb pattern along those peaks and nulls. Do I remember correctly? or even closely ?? >________________________________ > From: Ed Price <[email protected]> >To: [email protected] >Sent: Sunday, April 28, 2013 11:33 PM >Subject: RE: [PSES] Mode-stirred, Mode-tuned, Reverb - what's the difference? > > > >Re: Mode-stirred, Mode-tuned, Reverb - what's the difference? >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:[email protected]] >Sent: Sunday, April 28, 2013 7:23 PM >To: [email protected] >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 <[email protected]> >>To: [email protected] >>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 <[email protected]> >>Date: Sun, 28 Apr 2013 07:38:25 -0700 >>To: <[email protected]> >>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. To post a message to the list, send your e-mail to >><[email protected]> >> >>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 <[email protected]> >>Mike Cantwell <[email protected]> >> >>For policy questions, send mail to: >>Jim Bacher <[email protected]> >>David Heald <[email protected]> >>- >>---------------------------------------------------------------- >>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 >><[email protected]> >>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 <[email protected]> >>Mike Cantwell <[email protected]> >>For policy questions, send mail to: >>Jim Bacher <[email protected]> >>David Heald <[email protected]> >> >- >---------------------------------------------------------------- >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 ><[email protected]> >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 <[email protected]> >Mike Cantwell <[email protected]> >For policy questions, send mail to: >Jim Bacher <[email protected]> >David Heald <[email protected]> - >---------------------------------------------------------------- > >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 ><[email protected]> >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 <[email protected]> >Mike Cantwell <[email protected]> >For policy questions, send mail to: >Jim Bacher <[email protected]> >David Heald <[email protected]> > > - ---------------------------------------------------------------- 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 <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
