Design And Implementation Of Weather Facsimile Receiver Based On PCI104

Weather fax receivers is playing a significant role in ship sailing. It's a important way by analyzing fax images to improve a reasonable sailing route and its popularity ensures the safety of people.Most receivers now use superheterodyne architecture,which is low in digitizing and difficult to debug.Considering disadvantages of receivers now,we design receivers based on IF digitization.In this structure,the RF signal no longer need complex mixing process.Thus,the analog circuit is greatly simplified and digital integration improves.The receivers consists of front-part processing module,digital signal processing module and display and control module.Front-part module,which includes filtering circuit,amplifier,local oscillator and mixer,complete the work of RF signal's early process;digital signal processing module has A/D part,CPU and data buffer.Mainly,it has the task of bandpass sampling,controlling external devices,digital filtering and demodulation for FSK,storage and buffer for images,and finally accomplish data and order exchange between host and main controlller via PCI9030 bridge chip.By operating on client GUI,the control module could control receiving modes,display realtime status,exchange commands,generate,monitor and save images.Based on the principles and structure of digital IF,the paper complete the selection,verification and analysis of the sampling program.With the feasibility of .the program ,the paper complete the selection of core components and design of hardware schematics and PCBs.Then the paper designs the software program,including CPU's ISR program,control and initialization of external devices,software filtering and demodulation ane logical design of control signals. The program accomplish the function of control,and also achieve the purpose of receiving and processing images in Qt client based on Vxworks.The paper introduces the principles of receivers based on PCI 104 and complete analysis and design of each part.Carry out bandpass method instead of over-sampling to complete high-speed acquisition work against narrow-band signal.The method reduces difficulty of digital signal processing in baseband.Considering the accuracy shortage and poor reliability for analog circuits' filtering and demodulation,the paper designs the procedure of digital quadrature demodulation and digital filters. In case of the separation between client and server-side in earlier designs,the paper use Vxworks equipped with a graphical interface to complete the integration of both.By joint commissioning,we can say the method has reasonable selection and has excellent performance and feasibility .