Loran C tracking of land vehicles using microcomputers

The concept, design, and evaluation of two similar Loran C land vehicle tracking systems developed by MITRE are presented. One system was developed to provide field demonstrations of applications of Loran C location techniques such as highway inventory accounting, highway accident site recording, control and dispatch of emergency and law enforcement vehicles, and control of mass transit vehicles. The second system was configured to automatically display the reported status and location of two emergency medical service (EMS) vehicles to aid in more efficient dispatch and control functions. The Loran coordinates of the vehicle are transmitted to the base station where a microcomputer resolves the Loran coordinates into geographic/display coordinates and displays the vehicle location. Accurate Loran C land vehicle tracking requires calibration of the Loran signals to respective geographic or map coordinate locations. The two systems being discussed use a linear approximation of the hyperbolic Loran grid. The Loran coordinate to display screen position algorithm is, therefore, linear. Automatic tracking Loran receivers are installed in the vehicles. The receivers have been modified to output an audio band signal containing the two Loran time coordinates, the internal status of the receiver, a vehicle identification code, and 1 of 8 vehicle status codes entered on a manual keyboard located in the vehicle. A transmitter key control is also available. Commercial land mobile radios are used for transmission and reception of the audio signal. The land mobile receiver output at the base station is demodulated by a commercially available demodulator and input to the microcomputer on a serial port. After initialization of the system, map display, tracking, screen refresh, and status reporting are all automatic.