A measurement-while-drilling system includes a lower toroid, wherein the lower toroid has a lower toroid winding and is adapted to engage a mud motor shaft and is further adapted to receive a signal from one or more sensors and an upper toroid, wherein the upper toroid has a upper toroid winding; and a magnet disposed along the mud motor shaft within the lower toroid. The lower toroid and the upper toroid are disposed so that a signal from the lower toroid is induced in the upper toroid. The lower toroid winding is non-uniform so that the signal induced in the upper toroid is indicative of a rotation rate of the mud motor shaft.