Bob Heller asked: >> 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? <<
Accuracy and what regulatory authorities require are not always the same thing. It isn't hard to measure the magnetic field accurately, given a loop whose response is known (and which is either well balanced or shielded against E-field coupling) and an accurate receiver, analyzer, etc.. Near field or far field only matters when we want to know what one will be from the other, and this can be calculated. But do our regulatory agencies want to know the (accurate) result in dBpA/m? Usually not. They want dBuV/m -- and to simplify things, probably tell us to assume far-field conditions. Our measurements would then be reasonably precise -- and inaccurate. This is not necessarily a bad thing. It makes measurements faster and easier and *so long as limits are properly crafted* still protects victim devices. If everyone uses the same (inaccurate) method with reasonable precision, we'll get results that aren't wildly different from each others', so the tests we do will have a usable relationship to the real world even though the numbers are "predistorted." (It still bugs me. If an accountant predistorted our corporate bosses' books this way someone would go to jail. But in this case, it is probably good enough. C'est la vie!) Cortland Richmond KA5S 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
