This thesis deals with designing and implementing autonomous decoder for RTTY communication. Theoretical part of the thesis deals with researching the RTTY technology and FSK modulation, which it uses, focusing mainly on the methods of demodulation. Next part of the thesis compares suitability of available platforms. Practical part of the thesis describes the design and implementation of circuit board, firmware and computer application. The device is using STM32 microcontroller. Firmware was developed in C++ using Arduino. The computer application was created by using C\# and WPF. 3 methods of FSK demodulations were implmented. One is using a FFT algorithm. Other two calculate frequency based on the period of square signal.

Bibliography: pages 233-235. / The CCITT X.400 Message Handling System resides in the Application Layer of the seven-layer Reference Model for Open Systems Interconnection. It bypasses the services of the Presentation Layer completely to interact directly with the Session Layer. The objectives of this thesis are to show how the general Session Layer may be tailored to be minimally conformant to the requirements of X. 400; to produce a formal specification of this session layer; and to show how this session layer may be implemented on a real system. The session services required by X. 400 are those of the Halfduplex, Minor Synchronization, Exceptions and Activity Management functional units of the CCITT X.215 Session Service Definition. These services, and particularly their use by X.400, are described in detail. State tables describing these services are derived from the general session service state tables. Those elements of the CCITT X. 225 Session Protocol Specification which are required to provide only those services required by X. 400 are described in detail. State tables describing this session protocol are derived from the general session protocol state tables. A formal specification of the session layer for X.400 is presented using the Formal Description Technique Estelle. This specification includes a complete session entity, which characterizes the entire session layer for X.400. A session entity for supporting X.400 is partially implemented and interfaced to an existing X.400 product on a real system. Only the Session Connection Establishment Phase of the session protocol is implemented to illustrate the technique whereby the entire session protocol may be implemented. This implementation uses the C programming language in the UNIX operating system environment.