in a phase - modulated communication system utilizing voice - band communication channels wherein phase - jumps may be experienced , a phase - jump detector indicates the occurrence of such phase - jumps . a phase - jump corrector responds to the persistence of a phase - jump condition by correcting for it without requiring shut - down and complete reequalization of the transmission channel . monitoring of the incoming signal for phase - jump occurrence provides a convenient signal quality indication that represents the magnitude of the error in the x and y components of each received symbol .