Device for preventing traction power harmonic interference on high frequency track circuits

In a system for use along a railroad trackway, involving an AC track circuit including a plurality of tuned circuits connected to near and far running rails for indicating the presence of a vehicle, the improvement which comprises:

• an arrangement including a cancellation coil for canceling the circulating current which flows in the loop defined by said near and far running rails and is normally accepted by said tuned circuits, said circulating current being due to the differential induction of noise currents from said third rail to said far running rail and to said near running rail, respectively, said cancellation coil including means for inducing corresponding noise current from said third rail into said cancellation coil and from said cancellation coil into said far running rail, and means for avoiding the inducing of the noise current from said coil into said near running rail, thereby to effectively cancel said circulating current.