Theoretically, the transition from near to far field occurs at approximately lambda divided by 2pi. I've done countless measurements below 30 MHz, and all I can say is, measure it to find the fall off rate. I've seen from 40 dB/decade to 60 dB/decade in actual measurements (near field). One of the important factors to remember when doing these measurements is to avoid as much as possible doing them over a metal ground plane. The fields are primarily magnetic in nature, and therefore have a tendency to couple to the ground plane. As a note, the FCC will accept a 40dB calculation below 30 MHz unless a fall-off greater than that can be proved with measurements at multiple distances.
William M Stumpf DLS Electronics 166 South Carter St. Genoa City WI 53128 ph: 262-279-0210 fx: 262-279-3630 email: [email protected] From: John Woodgate [mailto:[email protected]] Sent: Monday, December 15, 2003 5:09 AM To: [email protected] Subject: Re: E-field drop off with distance (1-30MHz) I read in !emc-pstc that PLC Webmaster <[email protected]> wrote (in <002701c3c2a7$4299ab80$f8242052@default>) about 'E-field drop off with distance (1-30MHz)' on Mon, 15 Dec 2003: >I am currently researching the radiated emissions from High Frequency >Power Line Communications (1-30MHz). So are a lot of other people. > >I am trying to obtain information on how the e-field typically falls of >with distance. I have read books that have made claims that this is >anywhere in the rang 1/d to 1/5d. You mean 1/d^5. >I am trying to make a statistical >analysis to explain to those who claim that in the near field it is >(1/d^2) which they derive from an infitesimally small dipole. Statistical? What is statistical about the field pattern? > >Does anyone know of any papers, experiments or actual EMC compliance >measurements in the range 1-30MHz that I could use to make an analysis >of the drop off rate. There must be thousands. But there is a lot of commercially-available software that *calculates* field patterns for any reasonably simple physical set-up. Both symbolic and finite element analyses are possible. You seem to be proposing to invent the wheel. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [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 EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [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
