Patent GB-929496-A (GB)
Title: Radar
IPC: G01S7/295
Filed: 1959-11-27
Abstract: 929,496. Pulse radar. RADIO CORPORATION OF AMERICA. Nov. 27, 1959 [Dec. 24, 1958 (2)], No. 40490/59. Class 40 (7). In a vehicular radar system deflection scanning means on the display tube causes P.P.I. scanning, off-centring deflection means causes movement of the origin of scanning across the display tube screen in a direction and at a speed corresponding with that of the vehicle, means rotate the display tube and its deflection scanning means simultaneously in a direction opposite to vehicle turning motion, and apparatus operates when the origin of scanning approaches any edge of the display to automatically reset the origin of scanning to a point on the other side of the display. In the embodiment the point to which the origin of scanning is reset is such that continued motion of the vehicle (a ship) in the same direction will take the origin of scanning through the centre point of the display. The nature of the display afforded, as compared with a known north-stabilized display, is illustrated, Figs. 1, 2 and 3 (none shown). The embodiment is generally illustrated by Fig. 4, in which dashed lines indicate mechanical connections. A motor 60 drives the directional aerial 62 and a synchro transmitter 64 which feeds a synchro differential generator 66 with a signal of phase indicative of aerial direction relative to the ship's heading. Generator 66 drives servomotor 76 via a control transformer 72 and amplifier 74, and the motor rotates the rotatable deflection coil 78 of P.P.I. 54. A signal from the ship's gyro-compass over lead 39 actuates motor 40 coupled to reduction gearing 42, which provides a mechanical output to generator 66 and, with the P.P.I. stationary, a conventional north-stabilized display is produced. Shaft 44 is coupled to a synchro transmitter 46 to control a servomotor 52 which rotates a drum having mounted therein the display tube, coil 78, motor 76 and an off-centring coil 130. The drum is rotated in a direction opposite to that in which the ship turns so that the display shows all targets at correct bearings relative to the ship whilst avoiding smearing of the image when the ship turns. " True motion " is added by adding mechanisms 86, 88, respectively, driven by mechanical differential 90, the purpose of the latter being to compensate for the component of drift perpendicular to the direction of ship's motion; this compensation may be effected manually. The outputs of mechanisms 86, 88 are proportional to the sine and cosine respectively of the ship's bearing relative to north, and their output shafts 100, 102 lead to respective ball-and disc integrators 104, 106. The second inputs to the integrators are rotatable input shafts 108, 110, driven from a motor 114 which produces a shaft rotation speed proportional to ship's speed; the speed of motor 114 is also made dependent on the range on the P.P.I. The output shafts of the integrators are connected via magnetic clutches 122, 124 to three circuits, one of which includes offcentring potentiometers 126, 128 feeding orthogonal coils on yoke 130 so as to deflect the ship's mark across the P.P.I. in accord with the ship's movement; the second circuit includes resetting potentiometers 132, 134 to energize a relay when the ship's position has reached a preselected radius on the P.P.I.; and the third circuit includes mechanisms 152, 154 which reset the ship's position such that, if the ship's heading remains constant, the ship's mark will pass through the centre of the P.P.I. screen. Details of these circuits are described with reference to Figs. 6, 8 and 9 (none shown). An arrangement is included whereby, when the display is about to be re-set, a tone oscillator is actuated to warn the radar operator. Specifications 599,889 and 795,537 are referred to.