In this paper, the effects of linear time-variant channels introducing a time-variant delay are studied with reference to the class of the generalized almost-cyclostationary input signals. Specifically, the Doppler channels existing between a transmitter and a receiver in relative motion is considered in both the cases of constant relative radial speed and constant relative radial acceleration. It is shown that, when excited by an almost cyclostationary signal, in the first case the channel generates an almost-cyclostationary output signal whereas in the second case it generates a generalized almost-cyclostationary output signal.