Apparatus and method for generating a motional signature indicative of motion of moving parts of a target machine

The present technique provides an apparatus comprising receiver circuitry to receive a signal formed from a plurality of multipath signal components, including a first set of multipath signal components that have been subjected to modulation by interaction with at least one moving part of a target machine. The first set of multipath signal components have time varying signal paths due to the interaction with said at least one moving part. Evaluation circuitry is used to generate, for at least one property of the received signal, an evaluation signal, and modification circuitry then produces a modified evaluation signal by applying a removal operation to at least partially remove from said evaluation signal a contribution to that evaluation signal from the multipath signal components whose associated signal paths are non-time-varying. Thereafter processing circuitry performs one or more processing operations on the modified evaluation signal to produce a motional signature indicative of the motion of said at least one moving part.