Dear Dave, Thanks for your information. Since the local regulatory body set both E-Field AND H-Field limit for frequency range under 195kHz. But as I know, for all radiated emission measurement under 30MHz should use loop antenna, so I use EMCO 6502 for E and H- fields measurement. The spectrum analyzer dispaly (dBuV/m) with transducer factors ( magnetic antenna factor -51.5dB). For H-field, I used extrapolation factor "3" to calculate the corresponding limit at 10m ( becasue the document states the limits at 300m!) I used the reading on the spectrum analyzer plus (-51.5dB) then I can get the H-field value then I compare it with the extrapolated limit at 10m (measuring distance). For the E-field, I use the reading on the spectrum analyzer and compare with the limit at 10m (use the same extrapolation factor "3" to determine from 300m). Since theoretically, when the Tx & Rx antennas are both loop antenna, within the near field region, H field attenuate at the rate of 1/(r^3) and E-field attenuate at the rate of 1/ (r^2). My questions: I should use "2" or "3" for the calculation of E-field extrapolation? The mesurement methods is valid or not? I also thanks to all experts replied the message of this problem. Regards, Derek.
[email protected] 說： Dave, We have run the measurements at 300 m, 30 m, and 10 m and found the fall off of 1/R^3 apply because the magnetic field is being measured using a loop antenna. The far field E field rule does not apply for a magnetic field. Regards, Frank de Vall Sr. Engineering Manager - Compliance Assa Abloy ITG and HID Corporation drcuthbert@micron .com Sent by: To owner-emc-pstc@ie ee.org cc Subject 06/22/2005 08:29 RE: 璅?嚗?RE: Near field H-field AM measurement. Derek, in regards to the magnetic field measurement from 50 kHz to 1 GHz: You can figure that your measurement is in the far-field when the distance is >1/6 wavelength. At a distance of 10 meters this occurs above 5 MHz. So above 5 MHz the field will drop as 1/d and the difference between 300 meters and 10 meters is 30 dB. Below 5 MHz what is the difference between 300 meters and 10 meters? Let's run a?NEC-2 simulation?and see what we get. The antennas are 1 meter square loops in free space. I am comparing the current induced in the two receive loops placed 10 and 30 meters from the transmit loop. FREQ? ?0.25 MHz?? 82 dB ????????? 0.50????????? 69 ????????? 1.00????????? 57 ??????????2.00????????? 44 ????????? 4.00????????? 33 ????????? 8.00??????????30 I next placed the antennas 1 meter above perfect ground and obtained the same results. These results can be mathematically confirmed (I will leave that up to you) using the formulas I sent. It would be great if someone could run actual measurements at 10 and 300 meters. Once again we find that the FCC rules-of-thumb do not reflect reality. ?? Dave Cuthbert ?? Micron Technology This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: 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: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 有即時通知，收艂 -------------- ------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: 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: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
