try their website sara.com and look for the CASSPER system. At 08:33 AM 9/24/98 -0700, you wrote: >Scientific Applications and Research Associates has a Pre-Compliance test system which is said to be able to accurately measure emissions in the presence of Ambient signals. I believe the system is Called "CASSPER". > >For more info, > >Contact Ed Nakauchi >(714) 903-1000 x234 > > >Regards! > > >Randy Flinders >EMC Engineer >Emulex Network Systems >(714) 513-8012 >randall.flind...@emulex.com > >---------- >From: Keith Armstrong >Sent: Wednesday, September 23, 1998 7:35 PM >To: Thomas N. Cokenias >Cc: Muriel Bittencourt de Liz; emc-p...@ieee.org >Subject: Re: Doubt on Measuring with Spectrum Analyser > >Dear all >There is a UK EMC test equipment company called Laplace Instruments that >claims to have done considerable work on this sort of issue, having >found that A-B does not work. > >They have special software that uses a calibrated Comparison Noise >Emitter to compensate for site variations. It may also be useful against >ambients. It is a low-cost pre-compliance system and not intended for >full compliance tests. > >I only know of it through talking to them at the IEEE show in Denver. >For more info: their site is www.laplace.co.uk or you could Email David >Mawdsley at t...@laplace.co.uk. > >Hope this helps! >Keith Armstrong > >Partner, Cherry Clough Consultants >EMC-UK Associate >phone: +44 1457 871 605 >Fax: +44 1457 820 145 >Email: karmstr...@iee.org >Thomas N. Cokenias wrote: >> >> Muriel, >> >> It depends on how you are subtracting. >> >> When measuring with EUT on, you are looking at ambient + EUT signal - in a >> logarithmic representation when using the analyzer log scale. Since >> subtracting logs is equivalent to dividing numbers, you have to be >> careful. >> >> A worst-case scenario is when you have an EUT signal at the same frequency >> as an ambient, but at only slightly lower amplitude that the ambient. I >> don't know of any way of extracting the EUT signal using conventional EMI >> instrumentation. As I recall, using the subtraction function available on >> most analyzers will cancel out the ambient+EUT, giving the impression there >> is no EUT signal there. >> >> Your task is to reduce the ambients being received by your measuring system >> to a level more than 6 dB below the spec limit you are measuring to, >> hopefully by a lot more than 6 dB. Most specifications consider a >> measurement valid only if signal+ambient is at least 6 dB greater than >> ambient alone. This way, if the EUT signal is near the limit, you will see >> it come and go as you turn the EUT on and off. >> >> For line conducted tests, try using an AC EMI line filter at the AC input >> to the LISN, placed as close as you can to the LISN. The filter should >> attenuate the radio signals being picked up by the mains (antenna) wires. >> The LISN and the filter should be mounted on the same ground plane. I have >> had good results in on-site tests with LISNs, filters, and a portable >> ground plane. >> >> If you are still measuring strong ambients in the .150-30 MHz region, you >> may need to take steps to shield your equipment and set-up. >> >> Best regards >> >> Tom Cokenias >> Consultant, EMC & Radio Type Approvals >> >> --------- >> This message is coming from the emc-pstc discussion list. >> To cancel your subscription, send mail to majord...@ieee.org >> with the single line: "unsubscribe emc-pstc" (without the >> quotes). For help, send mail to ed.pr...@cubic.com, >> j...@gwmail.monarch.com, ri...@sdd.hp.com, or >> roger.volgst...@compaq.com (the list administrators). > >--------- >This message is coming from the emc-pstc discussion list. >To cancel your subscription, send mail to majord...@ieee.org >with the single line: "unsubscribe emc-pstc" (without the >quotes). For help, send mail to ed.pr...@cubic.com, >j...@gwmail.monarch.com, ri...@sdd.hp.com, or >roger.volgst...@compaq.com (the list administrators). > > >--------- >This message is coming from the emc-pstc discussion list. >To cancel your subscription, send mail to majord...@ieee.org >with the single line: "unsubscribe emc-pstc" (without the >quotes). For help, send mail to ed.pr...@cubic.com, >j...@gwmail.monarch.com, ri...@sdd.hp.com, or >roger.volgst...@compaq.com (the list administrators). > >
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