A method detects multipath propagation in a modulated digital signal. The method provides a first value of channel frequency, representing the modulated digital signal free of multipath propagation, providing a second value of said channel frequency, representing the modulated digital signal with multipath propagation, and comparing the first and second values. A method detects adjacent channel interference in a modulated digital signal by comparing first and second values of a characteristic parameter of the digital signal, respectively representing the digital signal free of adjacent channel interference and the digital signal affected by adjacent channel interference. In particular, the method obtains a derivative signal, applies a non-linear Teager-Kaiser function to the digital signal and the derivative signal for generating first and second signals respectively representing energy content of the digital signal and energy content of the derivative signal, and processes the first and second signals for generating the second value.