We examine a long-lived ULF wave observed by Van Allen Probe on 13 October 2016. The magnetic field perturbations agree well with model predictions associated with antisymmetric waves generated by the ballooning-mirror mode instability. The north/south oscillation in the equatorial line of nodes associated with the ballooning-mirror mode waves doubles the frequency of the compressional component of the magnetic field during these pulsations. The north-south oscillation of the transverse component of the ballooning-mirror mode waves also produces a shoulder-like pulsation in the observation of the transverse component. The results validate our understanding of the manner by which the waves produce frequency doubling and indicate that the method can be applied to future cases.