Abstract: After sampling and conversion into digital values, the digitalized temporal samples of the received code signal (SC) are subjected to a fast Fourier transformation, and the information items (FFT) representing the frequencies of the transform are processed automatically in such a manner as to compare spectra of the transform with stored theoretical values for each possible code signal, in order to determine a set of information items called "conversions" (M1-Mn), from among which a selector then selects a particular "conversion" (MSO) which will reliably identify the received code signal and will activate a display device.