Automatic frequency control in the presence of data

There is provided a method of and apparatus for Automatic Frequency Control (AFC) in the presence of data. It comprises removing the effects of data modulated onto the carrier (25), detecting the frequency difference between the carrier frequency and the phase of the reference oscillator (30), and adjusting (80) the frequency of the reference oscillator (35) to eliminate the frequency difference ( DELTA ). It is further characterized by digitizing (40) the modulated carrier in quadrature, sampling (20) the modulated carrier in quadrature at a multiple of the modulated bit rate, rotating phases toward arctangent (I/Q)=0 (25/55/60) to remove the effects of quadrature data (I/Q) modulated onto the carrier, detecting (30) the frequency difference ( DELTA ) between the carrier frequency and the frequency of a Voltage Controlled type of reference oscillator (35) with a phase trajectory estimator (45), and establishing and generating the requisite correction voltage ( DELTA ) for a Voltage Controlled type of reference oscillator (VCO) (35) with the phase trajectory estimator (45).