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

With the development of digital signal processing, self-adaptation, electronic countermeasures, computer networking, software radio and other modern technologies, shortwave communication is gradually developing to automated, intelligent, networkbased direction. Because of the anti-jamming ability, simple eq-uipment and easy for temporary networking,short-wave radio has become the preferred method of emergency communication,and have great value in research.The development of modern short-wave communications, architecture and design principles of software radio is analyzed in the paper. Software radio technology will be applied to short-wave radio, it can give a good solution to the traditional short-wave receiver which is not strong, inflexible, difficult to upgrade and can not meet the requirements of the modern short-wave communication.In this paper, the RF front-end of shortwave receiver's platform is mainly studied.Based on the analysis of structure, performance, strong point and weak point of several common receivers, the super heterodyne second frequency conversion RF front-end program is defined. Then, the main technical indicators of the receiver are analyzed, focusing on its sensitivity, noise and dynamic range. According to the requirements of the shortwave receiver for sensitivity, gain, dynamic range and image rejection ratio in this paper, the pre-filter, RF low noise amplifier, AGC IF amplifier and mixer modules are designed.In order to improve the sensitivity, enhance selectivity and stability, the short-wave band is divided into eight bands. Each band is tuned and band switch is achieved by inserting PIN with little loss. Chip microcomputer is used to control varactor diode's bias voltage to change its capacitance, so that the center frequency of the pre-selector's tuning circuit is changeable to achieve electronic tuning. Low-noise amplifier applies common-emitter common-base circuit, and is combined with pre-selector for dual tuner device. Meanwhile,using dual-gate FET 3SK223 to increase its automatic gain control. The IF AGC is divided into two levels, the first level is realized with 3SK223 and the second level is designed with two pillars of variable-gain amplifier AD603, Mixers Use Multiplier AD835, which is simple and feasible. Finally, the circuit board PCB of each module is produced and debugged, the corresponding technical indicators of each module are tested and analyzed, the feasibility and practicality of the design are verified.