  We present a method to identify spurious signals generated by finite-width
pulses in quantum sensing experiments and apply it to recently proposed
dynamical decoupling sequences for accurate spectral interpretation. We first
study the origin of these fake resonances and quantify their behavior in a
situation that involves the measurement of a classical magnetic field. Here we
show that a change of the initial phase of the sensor or, equivalently, of the
decoupling pulses leads to oscillations in the spurious signal intensity while
the real resonances remain intact. Finally we extend our results to the quantum
regime for the unambiguous detection of remote nuclear spins by utilization of
a nitrogen vacancy sensor in diamond.
