Abstract: 1. In a communication system utilizing at least two independent binary coded pulse signal sequences, means for achieving and holding time synchronism between said two sequences which comprises the combination of pulse recurrence frequency searching means for controlling the pulse recurrence frequency of one of said signals relative to the other to bring said signal into synchronism with the other, and phase locking means including a periodic phase checking circuit and a phase variation correcting circuit responsive to the searching means bringing the signals into synchronism to operate on one of said signals for holding said signals in synchronism.