The determination of the transfer function of the power line channel is a non-trivial task since it depends on several (often unknown) variahles: the topology of the network, the cahle parameters, the wiring and grounding practices, the impedance of the attached appliances, etc. The power line channel may vary abruptly when the topology changes, vhen devices are plugged in or out, and switched on or off. Moreover, the power line channel can he time-varying even if the topology of the network and the loads attached to it do not undergo ahrnpt changes. In fact, the power line channel is time-varying due to the appliances that are connected to outlets since appliances often exhibit an input impedance that is a function of the instantaneous amplitude of the mains voltage vililch, in turn, causes a periodically time-varying channel response. We propose here a discrete time-varying block channel model in the time domain that captures the cyclostationary nature of the channel response. Our model naturally allows for more realistic evaluation of modulation and coding strategies as well as for the design of bit loading strategies that can he resilient to the peculiar type of distortion encountered in this harsh medium.