Converting and decoding receiver for digital data recorded in analog form on magnetic tape

Claim 1

Apparatus for receiving data transmitted or recorded synchronously in the form of a multisptep-coded modulated wave signal modulated at least in part in multistep phase or frequency modulation, which data are subject to timing jitter and to sudden and short-interval, changes of amplitude after transmision or recording and before reception, said apparatus comprising an analog-to-digital converter, a quadrature pair of digital bandpass filters connected so that both said filters are supplied with output signals from said analog-to-digital converter, a decision circuit for selecting a complex data signal from a set of predetermined complex reference data signals which most nearly approximates a complex data signal constituted by contemporary outputs of said filters during intervals of predetermined length, said decision circuit being connected to the outputs of said filters by switching means defining said intervals and further comprising" means for clocking said analog-to-digital converter at a controllable rate in a frequency range in the neighborhood of a predetermined rate, determined from input signal characteristics expected from transmission or recording standards, in response to a timing control signal; means for deriving said timing control signal by comparison of input and output signals of said decision circuit and for applying said frequency control signal to said clocking means, and means provided in said filters for varying the propogation time therethrough of signals supplied by said analog-to-digital converter, and for accomplishing said variation in response to said timing control signal, said filters being constituted for providing stepwise variable propagation time therethrough without substantial change of filter bandwidth and being connected to said timing control signal deriving mans for propagation time control in response to said control signal.