I'd like to add a few comments about paths and victim circuits. The externally applied RF field may have more than one path into the EUT. Let's assume you have just two paths; one via a powerline that's equipped with a modest filter, and another that is a radiated path through ventilation slots.
The first path may allow energy between 30 MHz and 100 MHz to get to the EUT circuitry, but becomes a very lossy path above 100 MHz. The second path is very lossy below 2 GHz, but allows everything above that to get through. If you only tested for immunity up to 1 GHz, you would never know the second path existed. Any predictions about immunity performance of the entire EUT at 3 GHz would be misleading, since they would have been based only on observations of the performance of the first path. Now let's consider the victim circuitry. The electronics of the EUT are actually a large collection of tiny "victims", each with its own unique level of upset. If your EUT withstands everything up to 1 GHz without malfunction, that's still no guaranty that some collection of circuit traces and components will not have a resonance at 1.8 GHz, creating an upset condition. My point is that you can make decent predictions only if you know all the paths and all the victims. I have found that most real devices are so complex that performance predictions are wildly inaccurate. Rigorous testing is the only way to be sure. Regards, Ed Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military & Avionics EMC Services Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis >-----Original Message----- >From: Ken Javor [mailto:ken.ja...@emccompliance.com] >Sent: Thursday, January 10, 2002 12:41 PM >To: am...@westin-emission.no; emc-p...@majordomo.ieee.org >Subject: Re: RF immunity 1-2GHz > > > >I have a little different experience than the other >respondents to date, who >pretty much said no extrapolation is possible from one band to another. > >My experience and analytical training tell me that if field >intensity and >modulation are held constant, then above 1 GHz coupling to >wires running >between equipments will decrease with increasing frequency. If the >circuitry interfacing the equipments is slow with respect to 1 >GHz, and it >passed below 1 GHz, I would also expect it to pass above 1 GHz. > >If however the modulation scheme changes or the wires picking up the rf >energy are electrically short just below 1 GHz, then the immunity could >decrease with increasing frequency. > >A final consideration is how rf tight the equipment enclosure >is. A rule of >thumb of rf enclosure design is that slots and apertures >should be held to a >tenth wavelength long for good EMI performance. At 1 GHz, a tenth >wavelength is 3 cm. It is likely that as frequency increases >above 1 GHz >that imperfections in equipment enclosure homogeneity will >impact shielding >effectiveness. > >Ken Javor > > > > > > on 1/10/02 6:06 AM, am...@westin-emission.no at >am...@westin-emission.no >wrote: > >> >> RF immunity testing in the frequency range 80-1000MHz has >been common in EU >> for several years. Now, new standards also include testing >in the 1-2GHz >> band (3V/M or 10V/m, 1kHz sine, 80% AM) >> >> We have done a lot of testing in the 80-1000MHz band and >quite often the >> EUTs failed. We have also done some testing in the 1-2GHz >band, but never >> managed to disturb the EUTs in that manner so it fails (10V/m). >> >> What is your experience with RF immunity testing in 1-2GHz >band ? Do the EUT >> fail? >> >> On one specific product we have tested 80-1000MHz (no >failure) and emission >> testing 30-1000MHz (almost quiet, 20 dB margin). >> With these two tests performed, is it possible to assume >that we will pass >> the immunity 1-2GHz test ? >> The answer might be, test it and verify, but we would like >to argue that >> this test is not necessary to conduct, because to our >previous experience >> with RF immunity. Many of your might not like this approach >..... so be >> aware, this is just a question. >> >> Best regards >> Amund Westin, Oslo/Norway ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
