Way back once upon a time, we had tested a shielded chamber, that needed, according to the spec's, a SE higher than some number like you mention. Our initial testing revealed a few weak points. The several re-designs fixed those, but the purchase spec for the interface panel to the outside world was a compromise. We "patched" and documented the effort in order to test the rest of chamber to meet the spec's. And noted that the interface panel was the problem as it compromised the "system" Our reverb chamber was not big enough as it ran into these size related resonance modes that sent the results into unknown land. The testing did not involve any EUT equipment, and was just a shielding effectiveness test. Since I am a Vet and the product was supporting military efforts, I was somewhat tight on my interpretations of the requirements and results and the guy I handed the effort off to was active reserve. I pointed our that he might get called up and his arse depended on the performance of this equipment! - Bill
From: Ed Price <edpr...@cox.net> >To: EMC-PSTC@LISTSERV.IEEE.ORG >Sent: Thursday, May 9, 2013 9:29 PM >Subject: RE: [PSES] Mode-stirred, Mode-tuned, Reverb - what's the difference? > > > >Re: Mode-stirred, Mode-tuned, Reverb - what's the difference? >Bill: > >I was responding with the best anecdotal experience that I had on the subject, >but what I described was actually a big “science project.” I was testing, >actually, investigating might be a better term, the shielding effectiveness of >various compartments of what became the AGM-109 Tomahawk. That missile body >had more seams and flaps that a biker’s jacket! We needed to expose the >missile body to as high a field as possible to wring as much dynamic range as >we could for measuring the SE. “Enough” field was never really enough, as the >mechanical guys were sweating the designs to yield as much SE as possible. If >we could prove better SE, then the theoretical guys could calculate that a >mission could be flown closer to an emitter, thus influencing operational >flight and attack profiles. If we could show that one technique gave 128 dB SE >versus a different technique that gave 124 dB SE, rather than saying that both >techniques were equally better than 121 dB SE, then at least a few mechanical engineers were happier at the end of the day. And the new SE figure could mean that a flight didn’t have to take the long way to a target, instead, it might be able to thread its way between two hostile emitters. > >In that instance, we were not considering the response time of a victim >system, so all we cared was that the pattern shifted “enough” and that we >identified how long it took for the pattern to repeat. > >I didn’t understand what you were saying about “…skew the reverb pattern…” All >I know is that the stirring technique helped extend our SE dynamic range by a >little at around 200 MHz, getting more helpful until we had, IIRC, around 12 >dB betterment above 1 GHz. And 18 GHz was the high end of our investigation. > >Ed Price >WB6WSN >Chula Vista, CA USA > >From:Bill Owsley [mailto:wdows...@yahoo.com] >Sent: Thursday, May 09, 2013 12:53 PM >To: EMC-PSTC@LISTSERV.IEEE.ORG >Subject: Re: [PSES] Mode-stirred, Mode-tuned, Reverb - what's the difference? > >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 <edpr...@cox.net> >>To: EMC-PSTC@LISTSERV.IEEE.ORG >>Sent: Sunday, April 28, 2013 11:33 PM >>Subject: RE: [PSES] 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 >> - >---------------------------------------------------------------- > >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>
