| 摘要 |
PURPOSE:To make the interception of coded information difficult by combining an information signal and a carrier signal so as to generate spectrum inverting information. CONSTITUTION:An audible signal X(f) to be doded is given to a multiplier 4, where the signal is combined witha carrier signal Ce so as to generate an output signal to be subjected to spectrum inversion from the signal X(f) and a double side band wave having two times of the band width of the signal X(f) is obtained. The band of the output signal of the multiplier 4 is limited to frequencies 0-fc by a low pass filter LPF8 and becomes a coded signal E(f). If the frequency of the signal Ce is shifted vertically in a specified way or a program, the spectrum of the signal E(f) is changed in response to the deviation of the carrier fc and it is furthermore difficult for a user not permitted to receive the signal E(f) and decode it. |
