Abstract: Apparatus, which first de-interleaves a signal, that comprises a plurality of interleaved pulse trains, into its constituent pulse trains and then identifies the emitter which transmitted each pulse train, is described herein. Specifically, this apparatus comprises a folded shift register which performs the de-interleaving. The folded shift register comprises a plurality of serially connected identical "active" cells, each of which detects a pulse occurring at a particular group pulse repetition interval (PRI) and, in an embodiment described herein, ascertains the inter-pulse PRI for each detected pulse for use in identifying an emitter. One or more processors analyze the group and inter-pulse PRI data, provided by the folded shift register, in order to identify each emitter.