Abstract: In a circuit that detects from a received RF signal the digital signal modulated on the IF carrier signal by recovering the unmodulated IF carrier signal and comparing the recovered IF carrier with the downconverted RF signal, improvements are presented which minimize errors due to rapid and large phase changes in the RF signal. The circuit includes a downconverter (104) for downconverting the received RF signal to the IF level and a phase-locked loop (115, 118, 116, 119, 117) for both providing correction for relatively slow variations in the RF signal and for deriving the recovered IF carrier signal to which the downconverted IF signal is compared (108). Large and rapid phase changes in the RF signal are detected in a separate loop in the phase locked loop by monitoring (122) the sign and phase of the phase locked loop error signal for signals exceeding a predetermined threshold and rapidly advancing (123) or retarding (124) the phase of the recovered IF carrier whenever the threshold is exceeded.