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This can be calculated and I can send you the formulas. For a small magnetic loop the E-field falls off as 1/d^2 and 1/d. For a small dipole the E-field falls off as 1/d^3, 1/d^2, and 1/d. Dave Cuthbert Micron Technology From: owner-emc-p...@listserv.ieee.org [mailto:owner-emc-p...@listserv.ieee.org] On Behalf Of Brent DeWitt Sent: Thursday, July 08, 2004 7:11 PM To: T.Sato; emc-p...@ieee.org Subject: RE: FCC Part 18 - measurement at closer distance http://www.ieee-pses.org/symposium http://www.emc2004.org/ Tom, I have had experience submitting data taken at a closer distance than specified, although in this case it was 120kHz RF-ID systems. At close distances the FCC allows 1/d^2, but the reality is closer to 1/d^3 at 3, 10 and 30 meters. I simply took data at 3, 10 and 30 meters, and plotted to Excel to show the slope of the fall off (log distance). Never had a complaint. Brent DeWitt Loveland, CO http://home.ix.netcom.com/~bdewitt > -----Original Message----- > From: owner-emc-p...@listserv.ieee.org > [mailto:owner-emc-p...@listserv.ieee.org]On Behalf Of T.Sato > Sent: Thursday, July 08, 2004 6:44 PM > To: emc-p...@ieee.org > Subject: RE: FCC Part 18 - measurement at closer distance > > > http://www.ieee-pses.org/symposium > http://www.emc2004.org/ > -------------------------------------------------- > > On Thu, 8 Jul 2004 08:14:44 -0600, > drcuthb...@micron.com wrote: > > > I ran the sim again using perfect GND. The field falls off as 1/d. Over > > lossy ground it falls off much faster than 1/d. The antennas are 1/4 > > wavelength ground planes with the bases 1 meter above GND. Given more > > details I can make a better model. But in any case I don't think the > > field can fall off at less than 1/d. This makes the 1/d method safe to > > use. Safe in that you will not exceed the limits using this method > > although you might fix something that isn't broke and increase your > > product cost and pull down the aggregate productivity of the entire > > world (speaking as an economist would). > > Thanks guys. > > Yes, 1/d would be a reasonable assumption, I think. > And 47 CFR 18.305 (sorry, there was a typo in the first post) states > that we can make measurements at one closer distance and then use 1/d > as an attenuation factor. > > However, text of the note, > > 2. Testing for compliance with these limits may be made at closer > distances, provided a sufficient number of measurements are taken > to plot the radiation pattern, to determine the major lobes of > radiation, and to determine the expected field strength level at > 30, 300, or 1600 meters. > Alternatively, if measurements are made at only one closer fixed > distance, then the permissible field strength limits shall be > adjusted using 1/d as an attenuation factor. > > made me think that another extrapolation method may be permitted for > compliance with the section of the FCC rules, and somebody here may > have experience to use the method other than applying 1/d. > > That's why I posted the question here. > > Regards, > Tom > > -------------------------------------------------- > Tomonori Sato <vef00...@nifty.ne.jp> > URL: http://homepage3.nifty.com/tsato/ > > ------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. > > IEEE PSES Main Website: http://www.ieee-pses.org/ > > To post a message send your e-mail to emc-p...@ieee.org > > Instructions for use of the list server: > > http://listserv.ieee.org/listserv/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Ron Pickard: emc-p...@hypercom.com > Dave Heald: emc_p...@symbol.com > > 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: > > http://www.ieeecommunities.org/emc-pstc This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. IEEE PSES Main Website: http://www.ieee-pses.org/ To post a message send your e-mail to emc-p...@ieee.org Instructions for use of the list server: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com 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: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. IEEE PSES Main Website: http://www.ieee-pses.org/ To post a message send your e-mail to emc-p...@ieee.org Instructions for use of the list server: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com 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: http://www.ieeecommunities.org/emc-pstc
