Hi Ken, Group, As I present courses on EMC in the Netherlands, I have this demo-box with me. It consists of a welded rust free steel box with a clamp tightened cover. The joints have EMC fingers in perfect state. For miscellaneous experiments 5 6 mm (0.2") holes are drilled in it.
When I teach them about shielding I put my cellular in the box and ask one of the guys to call it. Great Surprise: it rings. Now I close all holes but one. It rings. Then I close the last one. It stops. The Dutch GSM provider sends at 1800 Mhz. If I considered a 10th of a wavelength for shielding, then I could allow for 16 mm. I have adjusted my lessons since then to adjust for this experiment and tell them that shielding only starts at 1/20th of a wave length. This was especially fun when I had these guys of Phoenix and other enclosure manufacturers in my Class. They are selling those 6 feet high 19"wide process controller enclosures to the industry having as "EMC cabinets" but they do not have a bottom in it to allow for cables to run. (they provide an earth rail, though) Regards, Gert Gremmen, (Ing) ce-test, qualified testing =============================================== Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ =============================================== >>-----Original Message----- >>From: owner-emc-p...@majordomo.ieee.org >>[mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Ken Javor >>Sent: Thursday, January 10, 2002 9:41 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. >>> >> >> >>------------------------------------------- >>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. >> >>
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