The Research Of An RF Front-end Circuit In Short-wave Receiver

There are many advantages of short-wave communication techniques. First of all,we can carry out the long range communication by short-wave without relay station.Then the construction and maintenance cost is low. Meanwhile, it has low devicecomplexity, so the circuit is easy to debug and the network is easy to set up. Also ithas strong anti-destroy ability against war and natural disasters. The entire advantagesmake the short-wave communication be widely used until now. With the developmentof the communication system, more requirements of communication system havebeen put forward. Therefore, new technologies of the short-wave receiver havebecome a hot-spot of current researches. This paper is mainly focus on the front-endcircuit (analog part) in a shortwave receiver. A kind of front-end circuit in an IF digitalshort-wave receiver has been designed and made out. Also there is a set of tests.The front-end circuit mainly uses one mixer and three automatic gain controllers.After mixing, the signal will be sent into the digital signal processor for subsequentprocessing. Three automatic gain controllers could insure that the system has enoughgain control ability. The former two gain control circuits which are located betweenRF front-end preselected filter and mixer and the last AGC circuit is behind the mixer.The structure of three AGC circuits cascade can provide over110dB dynamic range ofgain control in theory. The receiver can detect the electromagnetic waves of3~30MHz and generate the IF frequency of42.5MHz. The local oscillator signal rangesfrom45.5to72.5MHz. The content of this thesis is as follows:1. Introducing the detailed design of front-end circuit, including the design of themain function modules and the allocation of the main parameters and alsotheoretically demonstrated the feasibility of it.2. Designing6groups of high-performance front-end preselected filter whichcould improve the receiver signal selection filter and reduce the degree of outside interference.3. We design three AGC circuits which could improve the gain control ability ofRF and IF.4. The design of mixer and low pass filter.5. Welding and debugging of the circuit.The tests results show that the receiver is basically meet the design criteria. Thereceiver has a great dynamic range and excellent IF interference restrain and the noisefigure, sensitivity and frequency resolution also meet the design requirements. But theeffect of the IF output flatness and image rejection interference restrain is not ideal,which still need to be improved.