English: A loading coil for a 1922 AT&T long-distance telephone trunk cable between New York and Chicago. Loading coils prevent signal degradation on long distance lines and are still used in modern telephone systems. It consists of toroidal 0.175 H coils each attached to one of the circuits in the trunkline. 14 toroidal coils are strung on a spindle, shown leaning against the pot. Seven spindles fit in the pot, which is filled with oil. The pot will be mounted on a telephone pole. Loading coils are required at 6000 ft. intervals along the cable.