By measuring the E and H components separately, using near-field probes, which are, in principle, electrically short dipoles and loops. The biggist price to pay is the sensitivity, since they are electrically short. Also, they pick up the broadband field that gets detected in the detector circuit (DC output proportional to the field strength), so the frequency information is usually lost. Using isotropic probes can help, since it reduces the need for alignment of polarization. Unwanted pickup by the probe leads and the readout electronic, as well as the field perturbation by the probe and the operator sometimes cause considerable issues here. Neven
-------------- Original message -------------- > How would one go about accurately measuring low frequency fields say at 10 > kHz where the far-field even at lambda/6 is 5000 meters? > > Bob Heller > 3M EMC Laboratory, 76-1-01 > St. Paul, MN 55107-1208 > Tel: 651- 778-6336 > Fax: 651-778-6252 > ========================= > > > > "Price, Ed" > > om> To > Sent by: [email protected] > owner-emc-pstc@ie cc > ee.org > Subject > RE: ??? RE: ??? RE: Near field > 06/23/2005 11:24 H-field measurement. > AM > > > > > > > > > > > > > > -----Original Message----- > > From: Bob Richards [mailto:[email protected]] > &g! t; Sent: Thursday, June 23, 2005 7:06 AM > > To: [email protected] > > Subject: Re: ??? RE: ??? RE: Near field H-field measurement. > > > > Ken, > > > > I believe you are correct. There should be factors for this > > loop antenna from Emco that convert the raw reading (in dBuv) > > to a magnetic field level (like dBuA/m). > > > > The spectrum analyzer does NOT read in dBuv/m as he seems to > > suggest, it only reads in dBuv or dBm, but some analyzers do > > allow factors to be entered so the display will be in useful > > units. I prefer not having the analyzer apply factors. Less > > chance for errors that way, IMHO. > > > > Bob Richards, NCT. > > > > > > > EMCO (ETS) shows generic correction factors for the 6502 at: > > > http://www.ets-lindgren.c! om/product age.cfm/model/6502/producttype/Antennas > > < BR>> They have a pair of charts for correcting the antenna output (in dBuV) to > units of electric field (dBuV/m) or magnetic field (dBuA/m). > > > I don't like the practice of a factor for converting loop output voltage > directly to dBuV/m, because it is making the assumption of far-field > conditions (377 ohms, and an H-field to E-field conversion of +51.5 dB). > The 6502 is a shielded loop, and responds to the H-field, no matter where > you place it. You can accurately derive the E-field from the H-field only > when you are confident of far-field conditions. > > > Ed Price > [email protected] WB6WSN > NARTE Certified EMC Engineer & Technician > Electromagnetic Compatibility Lab > Cubic Defense Applications > San Diego, CA USA > 858-505-2780 (Voice) > 858-505-1583 (Fax) > Military & Avionics EMC Is Our Specialty > > > > ---------------------------------------------------------------- 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 ! > > -------------------------------------------------------- -------- > 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 ---------------------------------------------------------------- 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
