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This paper presents the theory of operation and an evaluation of performance of a delay-lock tracking system for binary signals. The delay-lock discriminator is a nonlinear feedback system which employs a form of cross correlation in the feedback loop and continuously estimates the relative delay between a reference signal and a delayed version of that signal which is perturbed with additive noise. Binary maximal-length, shift-register sequences are used as the signal because they can easily be regenerated with any desired delay and they possess desirable autocorrelation functions. Problems of target search and acquisition are studied. The system performance in the presence of additive Gaussian noise is discussed. Computations are made of the effect of amplitude-limiting the received data on the system noise performance.