The Design And Implementation Of RF Front-end Circuit In Short-wave Receiver

Short-wave communication technology is widely used in military, navigation and broadcast; it is also a meaningful way of emergency communications. With the development of signal processing technology and device performance, the analog devices are replaced by digital processors gradually; while the traditional short-wave receivers are evolve to the advanced digital receivers. In particular, the software radio technology based on fixed platform greatly promotes the research of digital short-wave receivers. The purpose of this thesis is the design and implementation of RF front-end circuit in digital short-wave receiver. The receiver system is implemented by a mixer and digital IF structure, and the RF front-end part of receiver is implemented by the pre-BPF, two auto gain control circuits, mixer and IF amplifier circuit. The system can process the RF signal with the range from 5MHz to 25MHz, and output a stable IF signal.This thesis introduces the key definitions of the indicators relevant to RF front-end, including the noise figure, third order intercept point, sensitivity, image and IF rejection degree. The parameters and feasibility of the system are demonstrated according to the calculation of each indicator. Then the design methods of the system are discussed based on system working principle, and the circuit diagram of each module is given in detail. The system hardware welding and debugging are completed and the testing methods of auto gain control circuit and system indicators are explained. The final test results are summarized and analyzed in the end. The results show that the RF front-end circuit in short-wave receiver has a wide range of gain controlling, and the dynamic range is greater than 90dB; all indicators except image rejection can meet the system requirements; the IF spectrum is ideal with a high SNR and good suppression to the second and higher harmonics.