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: kao...@sg.adi-limited.com.au > -----Original Message----- > From: Douglas McKean [SMTP:dmck...@corp.auspex.com] > Sent: Friday, 18 June, 1999 6:40 > To: emc-p...@majordomo.ieee.org > 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 majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
