| Nowadays, NTSC (National Time Service Center of Chinese Academy of sciences) is under building and perfecting the low frequency time-code service system which is a supplement to our country's time service system. Studying the system is a urgently and important project. In order to meet to the higher timing precision of the low frequency time-code timing terminal, the applications of DSP (Digital signal processing technology) in the time service is researched in this paper.The main works and contributions can be summarized as follows:(l)The low frequency signal transmission and DSP technology are discussed. According to the system needs, a testing flat of Low frequency time-code based on DSP is built up. The flat is used to observe the signal. In the second part, the principle of design, the realization methods of the hardware and software, and the selection of the devices are introduced.(2)To improve the timing precision of the receiver, it is necessary to research the timing reference point of the second signal. The reasons of the signal distortion are analyzed, and the relations of receiving bandwidth with distortion degree is discussed, for the more a steady point in the amplitude modulation signal is given by the method of the statistics. Looking at the point as the timing reference point of the receiver, the stability of the receiver is less than 100us.(3)The features of the low frequency time-code receiver aredigital, high performance and high precision. On the basis of the testing flat of low frequency time-code, we designed a low frequency time-code receiver based on software radio. The work is very helpful for the further studying the digitalization of the low frequency time-code receiver, and it may lay a foundation for our research. In chapter 4, The main concept and the key technology of software radio are discussed. Also the important digital theory such as FFT and digital filter are introduced in the last part.
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