AN ANALYSIS OF NORMAL-MODE NOISE CAUSED BY BRAIDED SHIELD CURRENT FLOWING ON COAXIAL-CABLE ATTACHED BY A FERRITE CORE

Since coaxial cables have excellent electromagnetic shielding characte ristics, they are widely used as interconnecting cables for digital in formation equipment. However, since braided lines are used in the shie ld layer of most coaxial cables, if an RF current flows, a noise volta ge (normal mode noise) is induced between the core wire and the braide d wire by electromagnetic coupling. Electromagnetic noise is also radi ated from the common mode current of the braided shield. It has been c onsidered that ferrite core loading is effective for reduction of the electromagnetic noise, and such loading is frequently used. In this ar ticle, in order to study whether ferrite core loading is effective in reducing normal mode noise, the normal mode noise generated by the bra ided shield current is analyzed with respect to the core loading locat ion. Next, a formula for the noise-reduction effect due to ferrite cor e loading is derived and its validity is demonstrated experimentally. (C) 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 1-10, 1999.