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At 13.56 MHz, wavelength is 22 meters. Depending upon the size of the EUT, 30 meters might or might not be in the far field of the EUT. If the EUT were small with respect to wavelength I would certainly expect 30 meters to be in the far field of the EUT - a tuned half-wave dipole develops the far field within a half-wavelength, some say within a sixth wavelength. Certainly at 300 meters you would be in the far field, so I can't understand how the NEC extrapolation is different than far field in this range. It would be interesting to know what assumptions were made to derive the field intensity profile. I hasten to add I know nothing about NEC or how you use it. > From: drcuthb...@micron.com > Date: Thu, 8 Jul 2004 07:52:27 -0600 > To: <vef00...@nifty.ne.jp>, <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 am assuming your device operates at 13.56 MHz. I ran a NEC-2 > simulation over "average" GND and the reduction in field strength is: > > DX 1/d NEC > > 30 m 0 dB 0 dB > 300 20 30 > 1600 35 58 > > So, according to NEC-2, the field strength falls off faster than 1/d. If > this is true then taking a closer measurement and using 1/d will over > estimate the actual field strength at the greater distance. If your > device is good at 30 or 300 meters then it is surely good at 1600 > meters. > > Dave Cuthbert > Micron Technology > > > > > -----Original Message----- > From: owner-emc-p...@listserv.ieee.org > [mailto:owner-emc-p...@listserv.ieee.org] On Behalf Of T.Sato > Sent: Wednesday, July 07, 2004 9:09 PM > To: emc-p...@ieee.org > Subject: FCC Part 18 - measurement at closer distance > > > http://www.ieee-pses.org/symposium > http://www.emc2004.org/ > -------------------------------------------------- > > Dear EMC experts, > > FCC Part 18 (46 CFR 18.305) defines field strength limit at very > long distance such as 300m and 1600m. > Fortunately, it is permitted to make a measurement at closer > distance: > > Sec. 18.305 Field strength limits. > ... > 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. > > Well, the latter method, adjustment with 1/d, is quite clear. > > But the former method is not clear enough for me - how should we > determine the expected level? > > Can we simply extrapolate the data at, for example, 3m, 6m and 10m > to determine the expected level at 300m or 1600m? > I think such extrapolation can cause quite large error in the result. > > Does anybody here has experience to use the former method for compliance > test, or does anybody knows of more detailed requirements or guidelines? > > 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
