GB591322A - Improvements in navigating apparatus - Google Patents

Abstract

591,322. Radiolocation. O'KANE, B. J., and DICKIE, E. J. May 16, 1945, No. 12370. [Class 40 (v)] In a pulse radar system with a P.P.I. display for use on a moving craft or vehicle, means are provided for controlling the rotation of the time base so as to maintain the orientation of the display with reference to some bearing other than the instantaneous course bearing, e.g. true or magnetic north or the track of the craft. As shown in the Figure, a saw-tooth time-base voltage from the generator 8 is applied to the rotor winding 9 of a rotary transformer and the outputs from the two perpendicular stator windings are applied to the. perpendicular deflection systems of the cathode-ray tube 7, the rotor 9 being mounted on the same shaft 3 as the aerial 1 so that rotation of the aerial by the motor 6 causes a synchronous rotation of the radial time base 15. The time base is initially set up so that the top of the P.P.I. display represents true north and in order to compensate for changes in the orientation of the craft the stator windings are mounted on a rotatable frame 10 geared to a repeater motor 20, which is connected to a distant reading compass 21. Alternatively, if it is desired to orientate the display in relation to the track of the craft the navigational instrument may comprise a drift angle computer. In a modification, Fig. 2 (not shown), the radial time base is produced by a rotary potentiometer having two 90 degree displaced wipers the voltage outputs from which are proportional to the sine and cosine of the angular position of the spindle and are applied to control the amplitudes of two sets of synchronous square waves which are applied through R.C. saw-tooth generating circuits . to the X and Y plates of the cathode-ray tube. The orientation compensation is obtained by gearing the aerial shaft and the navigational repeater motor to the two sun wheels of a differential gear, the potentiometer spindle being geared to the planet wheel. Alternatively, the rotary potentiometer could be replaced by the rotary transformer of Fig. 1 with fixed stators or the compensation system of Fig. I could be applied to the rotary potentiometer.