| Conventional transceiver depends on hardware much more. The emergence of software radio results in transceiver's renovation. The basic idea is to sample RF signal, process the digital signal by installing different softwares to implement different functions on a high-speed DSP platform. Due to the limitation of device level, it is impossible to sample RF signal in direct now and have to choose the middle project---sampling IF signal, using special chips to build the intermediate frequency module. This paper discusses the realization of the digital intermediate frequency modul in software radio system. Firstly it expatiates on the theory of software radio, discussing the Multi-rate Sampling, Digital Up/Down Converting(DUC/DDC), Digital Signal Modulation/Demodulation and the synchronization problem. Then on the basis of those, a scheme of the system is given, and the hardware circuits is built with appropriate chips. In succession, it discusses the software programme development flow. Finally, Its feasibility is analyzed by simulating the A/D, DUC/DDC, DPSK signal's coherent demodulation and carrier synchronization.
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