Abstract: Phase rotation of an input digital signal is effected by applying the input signal to a look-up table in a memory together with a rotation control signal. The output of the memory is the phase rotated signal. To reduce the size of the PROM required for the look-up table advantage is taken of the symmetry of the quadrants through which the signal may be rotated. With a maximum 0.degree. to 360.degree. phase rotation range divided into four 90.degree. quadrants a look-up table is only required for one quadrant. Thus the quadrant which the input signal is in is determined and the input signal transformed to correspond to the one quadrant by simple logic external to the PROM.

Abstract: A NAVSTAR receiver in which the received signals are processed to produce digitized quadrature signals at zero i.f. Baseband phasor rotation to effect Doppler tracking in the receiver loop is accomplished by deriving digital signals representing sin .omega.T and cos .omega.T for the required rotation angle .omega.T, multiplying the quadrature signals separately and summing the outputs according to the algorithm I.sup.1 =I cos .omega.T+Q sin .omega.T and Q.sup.1 =Q cos .omega.T-I sin .omega.T, where I & Q are the digitized quadrature signals.

Abstract: A receiver for a Navstar satellite navigation system wherein the satellite signals are down converted into zero i.f. quadrature signals (70a, 70b) and digitized (71a, 71b). The digitized signals address a PROM (72) together with additional bits representing phase rotation information (74) and locally generated code signals (e,l,p). The PROM is loaded with data in the form of "look-up" tables incorporating combinations of all input signal conditions whereby the combined address signals effect correlation and phase rotation simultaneously of the received signals.