Proposal of isomorphic emphasis in spectrum inversion of analog PM channels and its noise reduction effect

In order to guard against infringement of confidentiality in mobile communication, the idea of adding an encryption function to radio communications has been studied from various approaches. However, the existing methods have the defect that the frequency occupancy bandwidth is enlarged by the increase of effective modulation index, or that complicated circuits are implemented at huge cost. With such a background in mind, the authors establish an appropriate circuitry realization method and economical optimum configuration for isomorphic emphasis. Isomorphic emphasis suppresses the noise power well, even if a spectrum inversion encryption is introduced into PM transmission