Abstract: An EMC filter for a balanced multi-wired telecommunication line has an oblong closed magnetic path core 50 having at least one first core arm 50a with a first length and second core arms 50b with a second length which is equal to or shorter than the first length, and a plurality of coils 51 constituted by at least one pair of wires. The at least one first core arm 50a and the second core arms 50b constitute a closed magnetic path. The wires of each pair are closely positioned each other and wound around the at least one first core arm 50a so as to produce magnetic fluxes in the first core arm 50a flowing toward the same direction when a common-mode current flows through the wires. Each of the coils 51 has a signal input end and a signal output end, and the wires run in a one-way direction from the signal input ends to the signal output ends, respectively.

Abstract: An ac line filter comprises two main cores, at least one auxiliary core disposed between the two main cores, and a pair of windings provided on the main and the auxiliary core. The main cores form shell type closed magnetic paths and enclose the auxiliary core, which forms a closed magnetic path, when the two main cores are placed one over the other. Each of the windings is wound in a concentrated manner to surround both the inner core of the main core and the auxiliary core at a location where the auxiliary core is positioned beside the main core, and is wound in a spaced manner around the inner core of the main core at a location where the auxiliary core is not positioned adjacent the main core. Each winding is divided at the center thereof and the divided ends of one winding are cross-connected with the similar divided ends of the other winding.