| 摘要 |
PURPOSE:To reduce remarkably a locking time from the transient state to the steady-state by detecting two kinds of levels in a pilot signal reproduced from an erasure head and using the result of detection to apply tracking control and switching the signal processing state of the tracking control. CONSTITUTION:A local pilot signal is superimposed on an output of a head 24 to extract f1, f3 components as 3fH component and f2, f4 components as 2fH component. When the local pilot signal is applied conversely in this case, the quantity of generation of both the 2fH component and the 3fH component is decreased. A switch 49 outputs alternately the f2, f4 components at the steady state and applies the result to a multiplier 34. When both the output of comparators 41, 42 are at L level, an output A is obtained from a logic circuit 44 and the transient state is discriminated, a one-shot multivibrator 52 is triggered attended with the output and a clock pulse is fed to a 1/2 frequency divider via an OR gate. Then the local pilot signal is switched between the f2 and f4 components and the state is locked momentarily to the state close to the steady state.
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