A signal acquisition and distance variation measurement system for laser ranging interferometers comprising a signal acquisition unit. This unit comprises a frequency detection subsystem to detect the frequency of a received laser beam measurement signal which is buried in noise, wherein the subsystem comprises an acquisition subsystem with a wavelet packet decomposition unit and a phase/frequency detector PLL; a main PLL unit being coupled to the frequency detection subsystem for receiving the detected frequency of the measurement signal for phase estimation of the measurement signal; and a phasemeter band detection subsystem for detecting whether the measurement signal frequency is higher or lower than a reference signal frequency of a reference laser beam by operating a known change to the frequency of the reference signal and measuring the consequent change in the frequency of an interference signal for having the phase of reference signal locked to the measurement signal phase.