Complex sentence: They may serve, for example, to expand the broadcast range of a television or radio station beyond the primary signal's coverage area, or to improve service in a part of the main coverage area which receives a poor signal due to geographic constraints.
Split into simpler sentences: They may serve, for example, to expand the broadcast range of a television or radio station beyond the primary signal's coverage area. Or, they may serve to improve service in a part of the main coverage area which receives a poor signal due to geographic constraints.