A real-time digital detector for bifrequential coded signallings

It is shown that the detection of bifrequential codes in telephonic signals can be advantageously carried out by means of numerical algorithms. The input samples are weighted with the Hanning window and shifted in frequency in order to minimize the leakage errors introduced because of the finite time record length. The detection algorithm efficiency is very high because analyzed sequences remain real-valued still after the frequency shift and because only the spectrum samples of interest are evaluated. The characteristics of the adopted CPUs affect the real-time performances; nevertheless, several telephonic channels can be monitored with a first-generation DSP.<<ETX>>