In mobile radio system speech transmission between one base station and mobile users can be easily implemented. If the base station is engaged to one of the mobile users, the other mobile users cannot communicate with that base station. In order to solve this communication problem the message has to through a encryptor to scramble or encode message according to the same encryption technique implemented on the key code. At the receiver, the reverse scrambling process technique is performed by using the same key to unlock the code. For the purpose, the project attempts to design and build the encryptor and decryptor devices for speech transmission and reception.