a coherent demodulator for recovering the phase modulation from an input intermediate frequency signal includes a phase locked loop having switchable frequency and phase detectors . during initial acquisition the phase locked loop frequency is adjusted to be equal to the input intermediate frequency by comparing the loop frequency with the input frequency in the frequency detector and using the resulting error signal to adjust the loop frequency . after acquisition the phase detector maintains the loop frequency phase locked to the input frequency by now using the resulting error signal to adjust loop frequency phase , the error signal from the phase detector being the recovered phase modulation . a second control loop includes a narrow pass filter tuned to the desired frequency of the loop frequency . the error signal from the second loop is summed with the first mentioned error signal to precisely maintain loop frequency .