Abstract: A jitter canceller cancels time-variant signals in telephone lines resulting from 50 or 60 Hz commercial power sources which a phase locked loop will fail to absorb. The jitter canceller uses an adaptive filter having a tap coefficient which is not reset to "0" and forced to converge before a data transmission allowing use with telephone lines with multiple modems connected to a single line. The jitter canceller uses a phase rotating circuit, two phase difference detectors, and the adaptive filter to rotate the phase of an incoming signal by a phase predicted by the adaptive filter in order to cancel jittering.