VHF Communication System Based On VC Program Control

With the development of shipping industry, maritime traffic safety has been concerned much more than ever before. However, the present system cannot meet the needs of ensuring ship's navigational safety; therefore, upgrading the present communication system technology is the top priority.This system is baced on the Visual C++6.0 programming platform which can make VHF equipment controled by computer serial port, and realized the function of remote controlling VHF transceiver by the technique of computer network communication and audio multimedia; Thcence provides proposals for achieving unattended to VHF equipment.The system is designed to three modules:server application program,client application program and hard-wired. First the server program is the main control unit for collecting audio data, saving records and rewinding, then transmitting the audio data to the client by net. Server program creates database for saving ship information, and displays the dynamic information on ECDIS by GPS. Second the client application program realizes intelligent controlling to serial port:the audio detection method can identify whether the audio signal existed or not and then according to the result transmit VHF signals by computer serial port for controlling the PTT (switch) of interphone. Furthermore the hard-wired provide common interfaces for connection of computer serial port and VHF equipment, and unify the control level of devices.This design is increased three technical merits after the functions realized, which can improve the performance of the system. The first is compressing and decompressing audio signals, to reduce audio latency and improve system instantaneity; the second is realizing codec algorithm to avoid the data corruption during network transmission, and improve system security;the last is realizing the remote features from servers to clients, to ensure the maintaining of clients at any time,and improve system reliability.The system has past the LAN and public network tests and can realize the system function, and has a long time high stability, clear speech signal, low latency rate, and also meets the needs of remote controlling the VHF equipment. The result has been applied to the Jiling Ministry of Communication Technology Projects which is undertaken by GNSS Institute in Dalian Maritime University.The project's name is "watercraft dynamic monitoring information system". The research result has had application in the project.