A digital data communications system employing correlation detection is disclosed as comprising an encoding system which encodes successive k-bit data words from a data source into predetermined start-stop phases of either a 2.sup.k -bit repeating pseudorandom binary code or a 2.sup.k -l bit repeating pseudorandom binary code and a decoding system which receives the stream of ones and zeros in the pseudorandom binary code from the encoder and reproduces therefrom, using a correlation detector and associated circuitry, a replica of the original k-bit data word from the data source. Undesirable signal variations in the output of the correlation detector caused by a frequency translation error introduced in the transmission and reception of the pseudorandom binary code is eliminated by a feedback system which detects the effects of the frequency translation error at the output of the correlation detector and applies a frequency correction signal component to the pseudorandom binary code which offsets the frequency translation error prior to introduction of the pseudorandom binary code to the correlation detector. In lieu of the feedback system, a frequency translation error can also be minimized through the use of minimum shift keying (MSK) encoding and decoding apparatus respectively provided in the encoding and decoding systems, upstream of the correlation detector.