Design And Realization Of NAVTEX Receiver Based On ARM

Navigational Telex (NAVTEX) system is based on narrow-band direct-printing telegraphy, which is used to send and automatically receive information on safety of maritime navigation such as navigational warnings, meteorological warnings, meteorological forecasts and other urgent information. This system is an important part of the Global Maritime Distress and Safety System (GMDSS), playing an extremely important role in ensuring safe navigation of the ship. According to GB/T 18766-2009 the author designs a bilingual, dual-channel NAVTEX Receiver in this paper. The receiver support for simultaneous reception of international stations (518KHz, broadcast in English) and domestic stations (486KHz or 4209.5KHz, Chinese broadcast).Based on the analysis of the NAVTEX system principle and on the basis of technical requirements, the author completed the system project design of the receiver. The receiver uses Cortex-M3 family ARM chip LM3S9B96 produced by Texas Instruments as the controller, constructs a hardware platform including a RF receiver module, a information processing module and a LCD module. The receiver realizes the function of carrier amplification, mixing, demodulation, decoding and message displaying. In the RF receiver module achieve the mirror image of interference suppression, signal amplification, carrier demodulation and FSK demodulator, and resulte the carrier signal in digital baseband signal. Then the digital baseband signal been send to the information processing module through level converter circuit.Also in the RF receiver module, Direct Digital Frequency Synthesis (DDS) is used as the local oscillator, which improves the accuracy of the frequency output and the performance of the receiver. Automatic Gain Control (AGC) circuit with AGC integration chip is designed, which can simplify the receiving circuit and improve the dynamic range of the receiver.In the information processing module, Cortex-M3 Series ARM is used as processor, which can simplify the external circuit and connect to the network or printer through the on-chip integrated USB port and Ethernet port. Using dot-matrix liquid crystal to display messages directly can read the message without printing. Meanwhile, use the SD card as the receiver's non-volatile memory for store message. A Speech Synthesizer is adopted in the information processing modules which extend the voice output function. Connecting to computer only by using one Root USB cable by integrated the JTAG circuitry into the information processing module, which can makes software updating easier. Based on the above, the author completed the circuit PCB plate, and receiver design of hardware and software debugging. Debugging results show that the oscillator circuit, mixer circuit and FSK demodulation circuit design requirements are met, which verify the hardware design is correct. Meanwhile, completed the software design and debugging, which including DDS control procedures, packet decoding process, human-computer interaction process and the message stored procedures. The test results proved that this receiver can receive and display NAVTEX messages accurately.