Modular contiguous channel multiplexer

This invention relates to a modular contiguous channel multiplexer (46) having one or more modules (41, 42) that produce an asymmetric filter function that is combined with responses from other modules (44) to produce an overall symmetrical response. The multiplexer (46) can have channels (1, 2, 4) arranged in any order of relative frequencies and one or more channels (3, 5) can be added or removed from the multiplexer (46) without disturbing the operation of the existing or remaining channels (1, 2, 4). A method of constructing the multiplexer (46) involves choosing a downstream channel first, then choosing sequentially the channel immediately upstream from the channel last chosen and choosing filters (f, f1) of each channel to meet certain criteria. The filters (f, f1) of each channel are identical to one another but are not necessarily identical to filters (f, f1) in adjacent channels.