Abstract: In a communication system, in which a great number of communication stations operate on the same telecommunication channel, such as a radio frequency, secret information transfer for selective calls as well as group calls is secured by cryptographic transmission of speech signals, in which enciphering and deciphering of the speech signals in transmitting and receiving stations, respectively, are performed by means of a secret binary transformation code associated selectively with the speech communication in question.

Abstract: A disc shape rotatable coding member for programming of a radio communication apparatus. The coding member has notches or teeth around its periphery which cooperate with a detent and permit indexing selection of disc positions that are indicated by a number of radials, intersected by a number of imaginary circles, each forming a row of spaces, thus rendering intersection points between the radials and the circle. The intersection points may be provided with empty spaces without holes, empty space with threaded holes, permanent projections in the shape of pressed-up protrusions, or of semipermanent projections in the shape of screws placed in the threaded holes. These screws may be placed in such a way that the screw head forms the protrusion or in such a way that the threaded part of the screw forms the protrusion.