Abstract: A digitally modulated signal of the FSK type is subjected to limiting and linear FM demodulation to produce a baseband signal which often fails to show clearly the serial binary digital signal because of distortion and disturbances prior to its reception. The amplitude of the base-band signal is digitally sampled (quantized) at a uniform sampling rate which is an integral multiple of the symbol rate of the base-band signal. A sequence of successive amplitude samples spanning at least a symbol period addresses, at twice the symbol rate a look-up table containing a set of stored signal patterns and correspondence of patterns within a predetermined degree of similarity is elicited at twice the symbol rate along with information on the degree of similarity, and also a synchronizing pulse when the amplitude pattern shows that a binary signal transition is detected at a particular part of the pattern of the amplitude sample sequence.