Servo encodement and detection system using tetra-orthogonal servo pattern

Claim 1

A servo track encodement system for positioning a magnetic head over a selected one of a plurality of data tracks on a magnetic medium, comprising a servo pattern recorded on said medium along with said data tracks, said servo pattern comprising a plurality of servo tracks, each said servo track having a reference signal recorded therein, said reference signal having the same frequency and phase in each of said servo tracks, each said servo track also having a control signal recorded therein, said control signals having a higher frequency than said reference signals, the phases of said control signals in adjacent ones of said servo tracks cyclically revolving in 90° increments through 90°, 180°, 270°, and repeating themselves every four tracks, the boundary between adjacent servo tracks defining the centerline of one of said data tracks, and means for detecting the amount of each type of said control signal in the total signal reproduced by said head to produce an indication of the position of said head relative to one of said data track centerlines.