Bob, You must be a crotchety old-timer like myself. Re the following from the appendix in MIL-STD-461E (it's there because I asked for it). The part I refer to is in italics.
"Placement of limits can be done in several ways. Data may be displayed with respect to actual limit dimensions (such as dBuV/m) with transducer, attenuation, and cable loss corrections made to the data. An alternative is to plot the raw data in dBuv (or dBm) and convert the limit to equivalent dBuv (or dBm) dimensions using the correction factors. This second technique has the advantage of displaying the proper use of the correction factors. Since both the emission level and the required limit are known, a second party can verify proper placement. Since the actual level of the raw data is not available for the first case, this verification is not possible." Ken Javor > From: Bob Richards <[email protected]> > Date: Thu, 23 Jun 2005 07:05:43 -0700 (PDT) > 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 anaylzers 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. > > > --- Ken Javor <[email protected]> wrote: > >> I may be reading this post wrong, but the -51.5 dB >> factor is not an antenna >> factor at all. It is the ratio of magnetic to >> electric field intensity in a >> plane wave. It is -20*log (377). The use of that >> number is quite >> approximate in the near field of the transmitter. >> >> From: Y W Leung <[email protected]> >> Date: Thu, 23 Jun 2005 11:41:41 +0800 (CST) >> To: [email protected] >> Cc: [email protected] >> Subject: ??? RE: ??? RE: Near field H-field >> measurement. >> >> >> Dear Dave, >> >> Thanks for your information. >> >> Since the local regulatory body set both E-Field AND >> H-Field limit for >> frequency range under 195kHz. But as I know, for all >> radiated emission >> measurement under 30MHz should use loop antenna, so >> I use EMCO 6502 for E >> and H- fields measurement. >> >> The spectrum analyzer dispaly (dBuV/m) with >> transducer factors ( magnetic >> antenna factor -51.5dB). For H-field, I used >> extrapolation factor "3" to >> calculate the corresponding limit at 10m ( becasue >> the document states the >> limits at 300m!) I used the reading on the spectrum >> analyzer plus (-51.5dB) >> then I can get the H-field value then I compare it >> with the extrapolated >> limit at 10m (measuring distance). >> >> For the E-field, I use the reading on the spectrum >> analyzer and compare with >> the limit at 10m (use the same extrapolation factor >> "3" to determine from >> 300m). >> >> Since theoretically, when the Tx & Rx antennas are >> both loop antenna, within >> the near field region, H field attenuate at the rate >> of 1/(r^3) and E-field >> attenuate at the rate of 1/ (r^2). >> >> My questions: >> >> I should use "2" or "3" for the calculation of >> E-field extrapolation? >> >> The mesurement methods is valid or not? >> >> I also thanks to all experts replied the message of >> this problem. >> >> Regards, >> >> Derek. >> > > ---------------------------------------------------------------- > 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
