Abstract: The acquisition means includes a voltage controlled oscillator, comparison means for comparing an input signal to a signal from the voltage controlled oscillator, filtering means and a summing network connected in a phase-locked loop and providing an output signal at an output thereof at the input of said summing network, a signal multiplying network connected to receive the input signal and a signal from the VCO of the phase-locked loop and providing an output signal approximately 90 degrees out of phase with the output signal of the phase locked loop and two all pass networks connecting the output signals from the multiplying network and the phase locked loop to two inputs of a multiplier which has an output connected to the summing network, the all pass networks being designed to shift the phases of the signals so that they are in phase when applied to the multiplier.