Abstract: There is disclosed a high frequency communication system of the type employing a high frequency terminal which terminal can transmit a processed signal in a transmitting mode or process a received signal in a receiving mode which terminal includes a first subsystem for voice processing, including a processor responsive to voice signals to provide a linear predictive coded voice signal at a given data rate which signal is coupled to a data modem subsystem that digitally encrypts said voice signal which data modem subsystem is coupled to a modem processor subsystem capable of processing said encrypted signal for providing frequency hopping, feedback equalization, intersymbol interference cancellation, error correction and interleaving to provide a transmitted signal which is relatively immune to jamming during said transmitting mode which includes a convolutional encoder means included in said modem processor subsystem responsive to said encrypted signal to provide a convoluted signal at a higher data rate than