Software Defined Radio (SDR) aims at bringing digital treatment chip closer to the antenna in a mobile terminal architecture. The main goal is to create a reconfigurable radio architecture accepting all the cellular or non-cellular standards working in the 0-5 GHz frequency range. But, in this environment, the analog to digital conversion and the digital operations face issues like power supply and processing speed. The idea is to interface a preprocessing circuit between the antenna and a Digital Signal Processor (DSP) to pre-condition the RF signal. This paper presents the design of an analog discrete-time device located between antenna and a DSP in standard radio architecture. It uses the principle of the Discrete Fourier Transform (DFT) to reduce the frequency of the DSP-input-signal treatment to fulfil the SDR purpose. It has been validated through system level simulation.