Abstract: A system and method for determining at least one physical quantity by means of a relation between a transmission signal and a reception signal, wherein a transmitter emits the transmission signal having a predetermined frequency through a signal path for reception as the reception signal by a receiver. A reference signal generator generates a reference signal having a frequency which has a predetermined fixed relation to the frequency of the transmission signal. The reception signal is mixed with the reference signal to produce an intermediate frequency signal, which is filtered to isolate a difference signal, converted to a digital signal and then processed digitally to determine a phase and/or amplitude relation of the respective physical quantity to be determined. The transmission signal, the reference signal and the digital signal are generated in phase-locked relation using a clock signal derived from a main clock pulse of a master oscillator.