A Design On Meteorological Facsimile Map Modulation System Based On PC And Performance Analysis

When the ships navigating in all oceans around the world,timely access to accurate weather information plays a significant role in overcoming unfavorable meteorological conditions,reducing losses caused by severe weather.It helps the navigation more safety,time-saving and economical.Currently the primary means of ships at sea to obtain weather information is receiving facsimile maps transmitted by wireless meteorological facsimile station.By using scanning technology,the photoelectric conversion device turns the weather information images and symbols into electrical signals.And then,the image signals are broadcast through the radio communication technology.The main purpose of the research work of this thesis is to develop a FSK modulation scheme based on a PC and a high speed digital to analog converter for the"Information Transmission and Modulation System" of a "Shore-based Meteorological Facsimile Radio Transmission System Improvement Project" and analyze the performances of the designed scheme through computer simulation and experiment.This thesis studies the historic development and current development of the fax machine.It also adequately studies the structure of meteorological facsimile system,the process of facsimile communication,technical indicators and weather fax signal format.MATLAB is used to simulate the modulation process,to compare and analyze all the factors affecting the performance of meteorological facsimile signals.At last,the whole scheme of meteorological facsimile signal modulation system based on PC and high-speed D/A board is proposed.In this program,PC is applied to fetch image signals and complete the FSK modulation.It also composes weather fax signals according to the image signal format and controls the high-speed D/A board.High-speed D/A,with a high-capacity memory and a stable clock,can change its sample rate continuously by programming.Its high performance guarantees the weather signal conversion and output steadily.Having considered demonstrating the performance of this system,it designs meteorological facsimile demodulation system which based on PC and A/D converter board.The received signals demodulated and stored in PC.It proves the reliability of the system.Both systems are designed under platform Visual C++6.0.Experimental results show that the design of meteorological facsimile signal modulation system based on PC can achieve the desired function.The output signals have smooth waveform and stable frequency.With the advantages of friendly interface,high reliability,it has considerable practical significance for meteorological facsimile system upgrading.