Servo system for controlling the position of a reading head

A servo system for controlling the position of a magnetic recording head relatively to the center of a selected data track in a magnetizable layer of a recording medium that is relatively movable with respect to the reading head and is provided with a plurality of spaced tracks entending parallel to each other, said system comprising means for receiving shortwave information signals and two ordered long-wave positioning signals, each of said long-wave positioning signals having the same frequency and a different phase, means for recording said information signals in successive tracks and for successively superimposing each ordered positioning signals in separate ones of said data tracks in longitudinal alignment with said short-wave information signals in the magnetizable layer in which the data tracks are recorded, said positioning signals having a wavelength of a magnitude sufficient to produce crosstalk in a reading head placed over said selected data track, the wavelength of said short-wave information signals being of a magnitude insufficient to produce a crosstalk signal in said reading head placed over said selected data track, the spacing between tracks in which adjacent long-wave positioning signals are recorded being equal to twice the spacing between the tracks in which the short-wave information signals are written, the adjacent recorded long-wave positioning signals having different phases, a magnetic reading head having a gap width substantially equal to the width of each track so as to scan the full width of a selected track and to simultaneously read all signals in said selected tracks and only the long-wave positioning signals in the tracks on either side thereof, said reading head producing during reading a composite signal, frequency sensitive electronic means for separating the two positioning signals read from the tracks on either side of the selected track from the composite signal, means for effecting a phase comparison between said positioning signals and for producing a servo signal which is a function of the deviation of the reading head from the center of the selected track, and means responsive to the servo signal for adjusting the relative position between said reading head and said magnetic medium to align said reading head with said selected data track.