A magnetic recording disk drive uses a phase-quadrature position-error-signal (PES) pattern and a servo signal demodulator that is insensitive to clock errors and phase-misalignment errors. The disk has angularly-spaced servo sectors, with each servo sector having radially-spaced servo tracks that contain a phase-quadrature pattern of servo blocks. A first band in each servo sector contains two generally like patterns radially-spaced in the servo track with the second pattern phase-shifted 90 degrees along-the-track from the first pattern. A second band in each servo sector is spaced along-the-track from the first band and also has two patterns like those in the first band, but with the phase shift of the second pattern being in the opposite direction to the phase shift of the second pattern in the first band. The demodulator calculates the true amplitudes of the servo signal from the measured amplitudes of the servo signals from each band to thereby remove clock errors and phase-misalignment errors.