When making near field measurements with a device which is a field probe, as opposed to an antenna, the principle is to use a probe that looks like the victim of interest, and placed at a distance and orientation that simulates actual usage.
In this case, covering the long, medium and shortwave bands, there are a variety of antennas in use, including both wire type aerials and loops, the latter both shielded and otherwise. Not quoting chapter and verse of any standard here, but if one were serious about controlling RE at these frequencies, the best approach would be controlling common mode conducted emissions on cables attached to the device, both power and signal. The limit would be based on the field intensity that would result from such conducted emissions at a separation which is deemed proper for typical use. In this manner, all the variables that would befuddle the test engineer are subsumed in a limit which is based on the maximum field intensity from a radiating cable; a simple problem susceptible to a closed form solution. Ken Javor Phone: (256) 650-5261 > From: John Woodgate <[email protected]> > Date: Fri, 6 Jul 2012 21:05:47 +0100 > To: Larry Stillings <[email protected]> > Cc: <[email protected]> > Subject: Re: FCC maximum frequency measurement > > In message > <B5113F712514D611BC3C00D0B769542201480F6C@cw-server.complianceworld>, > dated Fri, 6 Jul 2012, Larry Stillings <[email protected]> > writes: > >> FCC (ANSI C63.4 / C63.10) specifies a 60 cm shielded loop antenna for >> measuring radiated emissions from 9 kHz to 30 MHz (magnetic field, Rod >> antennas to measure electric field are not allowed). >> >> The limit is written at 300 meters up to 490 kHz and 30 Meters from 490 >> kHz to 30 MHz. However, since you tend to be in the magnetic field of >> the earth we make the measurement at some near field distance of 10 or >> 3 meters using 40 dB/decade extrapolation factor. > > Thanks, but I would find the results difficult to trust, considering the > likely background noise level. Also, the field is most likely highly > inhomogeneous, so that you can get every result you like (or don't > like). > -- > OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk > Instead of saying that the government is doing too little, too late or too > much, too early, say they've got is exactly right, thus throwing them into > total confusion. > John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used > formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://listserv.ieee.org/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: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/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: Jim Bacher: <[email protected]> David Heald: <[email protected]>
