Abstract: A sometimes positive and sometimes negative frequency deviation is associated to a given logic value. The deviation is positive during a certain period of time and then negative, the respective periods being determined so that the cumulated sums of the positive and negative deviation periods are practically equal. A device comprises to this effect an analyzer element for analyzing the asynchronous NRZ signal, having an analog integrator (1, 2) for measuring time, which actuates a switch (3) for selecting a control voltage (MOD) from three voltages. This analyzer element comprises a D-flipflop (2) to whose clock input (CP) is fed the asynchronous NRZ signal, with a resistance-capacitance feedback (4, 1) between its output Q and its input D, and with means (3) for connecting the output {overscore (Q)} of the flipflop (2) to its input D when the NRZ signal has a given logic level.