With regard to the CISPR 11 limits below 30 MHz. A magnetic loop measurement is made because the loop measurement is more accurate than an E-field measurement. The practice of converting the measurement to a far field equivalent electric field intenisty is purely an algebraic conversion.
> -----Original Message----- > From: Arun Kaore [SMTP:[email protected]] > Sent: Thursday, June 17, 1999 11:42 PM > To: '[email protected]' > Subject: Re: Near/ Far Field Correlation Issues > > > Hi, all > > You are absolutely right about correlation issues at 3 m/10 m, which > arise > predominantly from near field effects/ mutual coupling which is best > demarcated from the far field by the equation 2*D*exp 2/lambada. > Depending > on the size of the object under test, the 3/10 m correlation, > particularly > in the frequency range say 30-100MHz could be out by as much as 5-6 > dB > (Remember the Mutual Impedance Correction Factors in Table G4 of CISPR > 16-1, > they were supposed to fix Site Attenuation defects at 3 metres !!). A > baseline with some of the less complex artifacts would provide some > assistance. > > Pauls Cook is right in saying that both E and H fields ought to be > measured > and mutual coupling effects between loop and object under test be > accounted.(ie. the effect of the measurement transducer on the EUT) > > I have recently been quite puzzled by CISPR 11: 1992, when they > quoted that > below 30MHz the quasi-peak limits refer to the magnetic component of > electromagnetic radiation. Contrary to this the limits are specified > in > dBuV/m instead of dBuA/m (Group 2 Class A, Table 5)!! Now, Because of > the > frequencies, test object sizes and test distance lengths involved I > cannot > invoke the golden 120*pi rule and make the conversion. But, is this > what is > expected of a test house? > > Also, ITE frequencies have shot past 500MHz, is an equivalent CISPR 22 > frequency upgrade in the pipeline? > > > Arun Kaore > EMC Engineer > > ADI Limited > Systems Group > Test & Evaluation Centre > Forrester Road, St Marys, NSW 2760 > P O Box: 315, St Marys NSW 1790 > > Tel: 61 2 9673 8375 > Fax: 61 2 9673 8321 > Email: [email protected] > > > -----Original Message----- > > From: Douglas McKean [SMTP:[email protected]] > > Sent: Friday, 18 June, 1999 6:40 > > To: [email protected] > > Subject: Re: NEAR/ FAR FIELD CORRELATION ISSUES > > > > > > At 11:18 AM 6/17/99 +1000, you wrote: > > > > > > > Even now, correlation between 3 meters and 10 meters > > is not guaranteed. And further, 3 meter to 10 meter > > correlation is at least "better" (define better anyway > > you wish) in the horizontal. Vertically it's terrible > > (define terrible anyway you wish). At least in my > > experience. > > > > And a product could be analyzed as being constructed of > > a variety of antennas - slots, corner reflectors, tuned > > cavity, tuned arrays, and either electric or magnetic > > dipoles ... each reacting it's own way in the far field. > > > > Now I'm not going to say it's impossible, but it seems to > > me that one must assume something to begin with instead of > > being able to blindly take a surface current measurement > > or near field measurement of X and state confidently that > > it WILL be Y in the far field under all circumstances. > > > > That's ultimately what one would have to be able to do > > without regard to the product. After a few rounds with > > a particular product, I've done this. I'm sure everyone > > at some point has done this. But with NO prior history > > of the product, I don't see how it's done. > > > > Regards, Doug McKean > > > > > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
