I may be reading this post wrong, but the -51.5 dB factor is not an antenna factor at all. It is the ratio of magnetic to electric field intensity in a plane wave. It is -20*log (377). The use of that number is quite approximate in the near field of the transmitter.
From: Y W Leung <[email protected]> List-Post: [email protected] Date: Thu, 23 Jun 2005 11:41:41 +0800 (CST) To: [email protected] Cc: [email protected] Subject: ??? RE: ??? RE: Near field H-field measurement. 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] ?? 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: ?? ---------------------------------------------------------------- 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
