VITA 49 Radio DF : Using coherent digital receiver set with VC++ and Octave

Abstract: The objective of this thesis was to evaluate radio receivers that had been previously acquired for other tasks by the Swedish Defence Materiel Administration, for additional service in a radio direction finding (DF) system. The antenna, calibration signal generator and DF algorithm were provided. As the receivers used the VITA 49 frame format, much of the work involved the interpretation of the frame structure and contents. The other main challenges were to put the receivers into the correct internal state, to compensate the analogue phase errors due to cabling, and to correlate the digital frames according to the time stamps. The work was performed partly as a literature study and, during implementation, by using an investigative trial and-error method. Collection of reference signals, for later offline analysis, was made at the Swedish Defence Research Agency. The findings of the evaluation was that the receivers were phase coherent and that the VITA 49 frame format was suitable for DF use. An apparently systematic error of unknown origin rendered the DF results inaccurate, even though the precision of the results was high. The automatic gain control (AGC) of the receivers did not perform according to norm. If the systematic error is compensated for, and the AGC problem is eliminated, the receivers will function as a DF system using the manufacturer's instructions, with the provided antenna. The performance of the receivers in this setting was not a primary concern for the thesis, but was deemed to be acceptable. Suggestions for further development include finding the source of the systematic error, an automatic calibration function, a more thorough performance analysis, and code optimizations using multiple threads.