Design And Realization Of The Digital NAVTEX Receiver

Navigational Telex (NAVTEX) system is based on narrow-band direct-printingtelegraphy, which is used to send and automatically receive information on safety of maritimenavigation such as navigational warnings, meteorological warnings, meteorological forecastsand other urgent information.NAVTEX receiver is an important part of the Global MaritimeDistress and Safety System. Because of its important role in maritime security field, itreceives more and more national attention. At present, NAVTEX receiver technology andproduct in China are behind the international level. For this reason, we carried out the designand realization of the digital NAVTEX receiver.The paper summarizes the current development of domestic and international NAVTEXreceiver technology, also analyses system principles and technical requirements. Using ADI’sADSP-BF518F DSP as the core controller, it proposes the receiver’s overall scheme. Thereceiver can receive international packets(518KHz) and local packets(4209.5KHz or486KHz)simultaneously, save the message, display the message and achieve self-test, etc.The receiver’s hardware circuit includes filter, amplifier, mixer, local oscillation, self-test,A/D conversion, controller, human-computer interaction, storage, communication and so on.It completes mainly the band selection of the signal received by the antennas for,downconverting to the intermediate frequency signal, amplifying and conditioning signal,etc.The analog signal after conditioning will be converted by the analog-digital converter, andfinally input to the DSP processor for digital processing. Meanwhile, it use SD card, SDRAMor Flash memory to store packets, receiver’s working condition, site table, font library datasand sine table datas uesd in the digital down conversion, etc. The receiver also has some othermodules,such as LCD display, voice synthesis output, and remote communications and soon,which complete display and voice prompts of the received packets.and it receivespositional information of the INS in order to finsh automatic reception.The paper designes the receiver’s software which uses DDC, NCO, LPF, CICdecimation, HB decimation and digital demodulation technology as the theoretical foundation.This software includes DDS, A/D converter, DDC, demodulation, decoding of the packets,human-computer interaction and message storage, etc. It completes signal downconversion,demodulation and decoding, and message storage and display functions. Meanwhile, theprocessor can control the local oscillator, self-test and analog-digital conversion and so on.Based on the achievement of the system’s hardware, this thesis achieves the system’s software debugging using integrated development environment Visual DSP++5.0, such asDDC, digital demodulation and decoding. And complete the test of NAVTEX receiver’swhole performance which can correctly receive and display NAVTEX messages.