Every bit of the first three paragraphs is absolutely correct. That aspect of the rfi ought to be controlled which is most likely to cause a problem. In a band where a whip or loop are each possibilities, then both the electric and magnetic fields should be controlled, and separately measured.
61000-4-6 is the conducted immunity requirement that supports or supplants 61000-4-3 at frequencies below 80 MHz. Inherent in 61000-4-3 & 6 is the concept of intentionally transmitted rf from an antenna. The IEC decided a long time ago that 150 Ohms was a more representative transmission line impedance than 50 Ohms, and they are no doubt correct. Whatever the value chosen, once a signal has been coupled to a conductor, it is the source impedance of the conductor that is of interest. If it were desired at low frequencies to simulate a local source of very high or very low impedance fields, I would think an open-circuited parallel plate would work for electric fields, while a short-circuited plate or Helmholtz coil would work for low impedance fields. A comparison of the coupling from those types of fields compared to a plane wave is given in my 1997 IEEE EMC Symposium paper (Austin, TX). IMO, such test would only be for very special circumstances and do not warrant standardization as routine requirements. > From: Bob Richards <[email protected]> > Date: Fri, 24 Jun 2005 05:04:55 -0700 (PDT) > To: [email protected] > Subject: Re: ??? RE: ??? RE: Near field H-field measurement. > > Ken, > > I'm no expert, but as I understand it, making > measurements at low frequencies, measured in the near > field, it is possible to have a very high E-field and > very low H-field if the radiating source is high > impedance. The opposite is true if the radiating > source is low impedance, ie: high H-field, low > E-field. > > Also, if the coupling mechanism of the susceptible EUT > is primarily inductive, (low impedance) then a > high-impedance radiator will be less likely to cause > interference than a low-impedance radiator. > > If my understanding is correct (tell me if I am wrong) > then I can see the case for making low-frequency > radiated emissions measurements with both E-field > whips and H-field loops, with a limit specified for > each, such as is done for GR1089 testing. > > There also needs to be some insurance that the > immunity tests cover these two scenarios as well. I > wonder just how well the conducted immunity tests > relate. The 61000-4-3 test (with CDNs) is with a fixed > source impedance of 150 ohms. Theoretically there can > only be a 6dB increase in either current or voltage if > the EUT port has a very low or very high impedance. > > Bob Richards, NCT. > > > > --- Ken Javor <[email protected]> wrote: > >> In my opinion... >> >> The right limit is the limit which protects >> reception of broadcast signals >> in licensed bands. At low frequencies where the >> "antenna" is either a loop >> or whip, the limit would be ascertained using a >> typical loop/whip connected >> to a typical receiver. The most accurate limit >> would be the rfi level at >> the receiver antenna port that allows a specified >> quality of reception in >> the presence of the rfi. The measurement would be >> made at a specified >> distance from the rfi source. The limit would then >> be so many dBuV or dBm >> in a certain bandwidth, using a particular >> loop/whip. The loop/whip >> construction and transducer factor would have to be >> specified. >> >> This is the only technically proper way of doing >> things until you are at a >> frequency/distance from rfi source such that a far >> field measurement is >> possible. A field intensity limit allowing the use >> of any suitable antenna >> is only appropriate if a far field measurement is >> possible. >> > > ---------------------------------------------------------------- > 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
