Brent DeWitt <[email protected]> wrote (in <JFEKIIBLAHFLFLAPJDMDKENK [email protected]>) about 'What is in the position of the ferrite core?', on Tue, 30 Mar 2004:
>I just wanted to pitch in that Don's rather complete explanation of the >reality of ferrites on cables can also be viewed as a condemnation of their >use for generic cables. Being an old fart, I tend to use "radiation >resistance" rather than "wave impedance" when describing the antenna >function of a cable, but Don's term is probably better. One of the most >important things to be gleaned from his response is how terribly variable >the effect of the bead is. In my opinion unless source, termination and >cable length are defined, the use of a ferrite to reduce emissions from >cables is only an academic exercise or an attempt to "compliance shop" at >certification labs. There are significant advantages to be gained by >digging deeper into the product to reduce the mechanism that is producing >the CM current on the cable. > Indeed. These considerations vitiate any technical justification for including 'ready-made connecting devices' within the scope of the proposed new European EMC Directive **in the terms at present proposed**. It seems impossible to devise a method of testing such devices for which the result depends only on the characteristics of the device and not those of the things it is connected between. Incidentally, it appears that detachable mains leads are 'caught' by this new provision! -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
