1321798 Automatic phase control FURUNO ELECTRIC CO Ltd 19 May 1972 [27 May 1971] 23689/72 Heading H3A Apparatus for synchronizing a reference signal d with a received signal c in the form of bursts repeated at a predetermined rate T comprises; a frequency divider/phase shifter 4 for dividing down the output of a fixed frequency generator 5 to produce the reference signal d, having the same frequency as that of the input burst c; a comparator 3 comparing the signals c, d to detect the phase difference; a memory 6 for storing the detected difference during the period T; means for producing a control pulse train which divides the period T into n parts, n being proportional to the detected phase difference; and means for adjusting the phase shifter 4, by 1/n of the detected phase difference at each production of a control pulse of the train. In the embodiment of Fig. 1, the control pulse train is produced by feeding the output from the memory 6 and a divided-down output e from generator 5 to a unit 7 which produces a train of pulses f having a pulse width dependent on the detected phase error. This signal opens gate 9 to pass pulses from generator 5 to a counter 10 which produces an output pulse each time it fills, to adjust phase shifter 4. The unit 7, Fig. 3 (not shown), comprises a counter (12) which counts the pulses passed by gate 9 and which resets a bi-stable (13) to close the gate 9 whenever the count coincides with that stored in memory 6. In a modification, Fig. 4 (not shown) the units 7, 8, 9, 10 of Fig. 1, are replaced by an adder (21) and accumulator (22) which adds the output from memory 6 to the accumulated count under the control of the pulse train e to produce the control signal for the phase shifter. As described the apparatus is used in an Omega receiver, the signal c being the bursts of one particular received signal frequency as gated out by receiver 2.