  We provide an explanation of recent experimental results of Xue et al., where
full revivals in a time-dependent quantum walk model with a periodically
changing coin are found. Using methods originally developed for "electric"
walks with a space-dependent, rather than a time-dependent coin, we provide a
full explanation of the observations of Xue et al. We extend the analysis from
periodic time-dependence to quasi-periodic behaviour with periods
incommensurate to the step size. Spectral analysis, one of the principal tools
for the study of electric walks, fails for time-dependent systems, but we find
qualitative propagation behaviour of the time-dependent system in close analogy
to the electric case.
