Servo writing a disk drive from spiral tracks by shifting a demodulation window an integer number of sync mark intervals

A method of writing product servo sectors to a disk of a disk drive, the disk drive comprising control circuitry and a head disk assembly (HDA) comprising the disk, an actuator arm, a head coupled to a distal end of the actuator arm, and a voice coil motor for rotating the actuator arm about a pivot to position the head radially over the disk, the disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval, the method comprising the steps of:

• (a) using the head internal to the disk drive to read the spiral tracks to generate a read signal;
• (b) processing the read signal to detect the sync marks in the spiral tracks to synchronize a servo write clock;
• (c) using the servo write clock to open a demodulation window;
• (d) demodulating the high frequency signal in the spiral tracks into a plurality of servo burst signals during the demodulation window to generate a position error signal used to maintain the head internal to the disk drive along a first servo track;
• (e) using the head internal to the disk drive to write product servo sectors along the first servo track;
• (f) shifting the demodulation window by an integer number of sync mark intervals to initiate a seek to a second servo track;
• and
• (g) using the head internal to the disk drive to write product servo sectors along the second servo track.