O.A. Nokhrin, V.V. Pechurin

Modern HF modems provide the data communication in bandwidth of the standard telephone channel by modulation methods FM2-8 and KAM16-64 with modulation rates up to 2400 Baud spatial wave. The recognition of these signals is performed on the base is of the signal constellation. The necessary condition for the recognition is frequency and clock synchronizing. Inaccuracies by synchronizing make it to difficult, and even make it impossible to recognize the modulation type. To reduce the uncertainties about the modulation type under these conditions allows discrimination PM and QAM signals. To discrimination these signals it is recommended to use the excess coefficient of the waveform envelope distribution, which characterizes peakedness or flat-toppedness of the distribution. The waveform envelope distribution of the PM signals is a single-mode and peaked and the waveform envelope distribution of the QAM signals is multimodal and flat-topped. The rule of the PM and QAM signals discrimination is based on the threshold criterion, where the threshold value of the excess coefficient is within the range of -0,4; -0,3. The model tests have shown that probability of the correct PM and QAM radio signals discrimination under SNR db is 0,95.