A method for determining the filling level of a product in a tank using electromagnetic signals, comprising: a) generating a transmission signal having a predetermined length; b) propagating the signal towards the product; c) receiving a reflected signal; d) determining whether the received signal overlaps the transmitted signal in the time-domain; e) setting an overlap-parameter to 1 if overlap is detected, otherwise setting the overlap-parameter to 0; if the state of the overlap parameter is not changed and if no overlap is detected, generate a signal having a length exceeding the previous length and repeat step b); and if the state of the overlap-parameter is not changed and if an overlap is detected, generate a signal having a length shorter than the previous length and repeat step b); and if the state of the overlap-parameter is changed, determine the filling level based on the length of the transmitted signal.