Design And Implementation Of Weather Facsimile Receiver Based On DSP

Weather facsimile receiver can receive facsimile charts broadcasted by coast stations and get meteorological condition of the sea area, which can be used to ensure a safe navigation. The existing weather facsimile receivers have many shortcomings, such as complicated hardware design and digitization of low level. All of this restrict the improvement of receiver's performance and promote the range of use.The design of receiver based on DSP is developed for the shortcomings of existing receivers. This Receiver includes two parts:the RF front-end processing module and the control and display module. The first part, with DSP as the controller and processor, is used to receive and demodulate facsimile signal, It includes many circuit units, such as RF signal processing circuit, IF signal processing circuit, processor circuit clock circuit and power circuit. RF signal processing circuit is used for signal filtering, amplification and mixing; IF signal processing circuit is used for signal'4s automatic gain amplification and digital down conversion; processor is used to control module and do digital signal processing; clock circuit provide reference clock for the device; power circuit provides sufficient power output to ensure the normal operation of the various parts of the module. The functions of human-computer interaction, image display and data storage are completed by the second part, including controller circuit, memory expansion circuit, extended keyboard interface circuit, display driver circuit, real-time clock circuit, extended communication interface circuit and power circuit. The controller circuit is used to response keyboard commands, receive, display and store the demodulated data; memory expansion circuit is used for the transfer of command, status and image data with the RF front-end processing module and for the storage of image data; extended keyboard interface circuit is used for command input; display driver circuit is used for human-machine interface; real-time clock circuit provide time; extended communication interface circuit provide hardware channel for the communication between this module and other devices; power circuit ensures the modules' power supply.The receiver takes digital intermediate frequency program. Analog frequency's downconversation is taken only one time and signals'baseband demodulation is achieved by software, so the system hardware design is predigested, digital level is improved, and analog parts' noise interference is reduced. The use of DSP improve the ability of system's signal disposal and real-time characteristic; Digital down-conversion chip lower the frequency of IF-sampling signals and reduces the operating pressure of DSP; The Self-detect channel circuit detect the ability of the system's software and hardware;. User can input command throw the Keyboard circuit. Weather facsimile charts'screen display is more intuitive than printed out on the paper.The paper list the parameters of the receiver system designed, analyze the methods of design of each circuit unit in detail and give the test results. The feasibility of system design is proved.