Abstract: An echo receiving system is provided for periodically scanning a region for echo returns obtained in polar coordinates and for providing a visual display of such received echo returns in a rectangular raster format, such system comprising: a scan converter, responsive to the echo returns obtained in polar coordinates for converting such returns into rectangular coordinates; and, means for modifying such coordinate converted returns and for displaying such modified, coordinate converted returns in the rectangular raster format with displayed data being a function of the scan-to-scan change in echo returns from objects in the second region. With such arrangment, target build-up and target decay may be presented in the digitally generated raster display in a manner similar to that presented in an analog PPI display.

Abstract: This system accepts compass outputs from a wide variety of compass output devices such as stepper and synchro devices having different coupling ratios, supply voltages and carrier frequencies. The system then, as part of a PPI radar system, electronically converts these compass outputs without the usual intermediary electromechanical devices into real-time analog reference signals properly phased with respect to the radar timing to provide an electronically stabilized PPI. This is achieved by comparing the points of equal amplitude of any two phases of gyro compass synchro output signals and using these major transition points to provide a digital code indicating the angular position of the gyro output shaft; a microprocessor then transforms the code, by comparison with a previously stored position code into coded position change signals which are then used to change a stored angular value, representing the course of the ship.