Patent GB-817192-A (GB)
Title: Improvements in or relating to radar systems
Inventor: WATT JAMES
IPC: G01S7/24
Filed: 1956-10-22
Abstract: 817,192. Radar. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. Sept. 6, 1957 [Oct. 22, 1956], No. 32120/56. Class 40 (7). Relates to a shipbound radar with a cathoderay tube P.P.I. display whose origin is displaced by X and Y shift voltages in accordance with the movement of the ship so that an image spot corresponding to a fixed target remains in a fixed position on the screen of the cathode-ray tube. In a first embodiment, Figs. 1 and 2, the shift voltages are produced by resolving a voltage of constant amplitude into X and Y components of the ship's heading and applying the D.C. resolved components to respective integrating capacitors through switches operated cyclically by pulses of recurrence freq uency proportional to the speed of the ship as determined by a ship's log. In a second embodiment, Fig. 3, the pulses from the log are applied to a smoothing circuit giving a D.C. voltage proportional to the speed of the ship which is resolved into X and Y components which are integrated separately to give the required shift voltages. First embodiment. As shown in Fig. 1, a ship's log 1 produces a pulse each time the ship advances a predetermined distance, e.g. five yards, and each output pulse is differentiated and triggers a monostable flip-flop 6, 8 producing a corresponding 50 m.sec. pulse which energizes relay coils 11 and 12. The output from a 1000 c/s generator 15 is applied to the rotor 16 of a compass-controlled resolver and the sin 6 component (#= ship's heading) is applied to a phase sensitive rectifier 24 producing a corresponding D.C. voltage which is applied through a cathode follower 31, relay contact 14 and resistor 34 to an integrating capacitor 35 whose leakage must be negligible over a period of several hours. The contact 14 is closed each time the relay coil 11 is energized so that the resultant voltage across capacitor 35 is proportional in magnitude and sign to the E-W component of the position of the ship and this voltage is applied through amplifiers 37 and 40 to an X deflection coil 42 which may be a special shift coil or one of the two crossed timebase coils. Valve 37 is preferably an electrometer triode having a very high input impedance. A voltage proportional to the N-S component of the ship's position is produced by a corresponding unit 45 controlled by the cos # resolver output and the relay coil 12. The origin of the display is reset by a push buttons 48 which changes the capacitor 35 to a voltage determined by the setting of a potentiometer 49; the button 48 is ganged to a corresponding button in the unit 45. The relay contacts 14 may be provided. with a guard ring to minimize leakage as described in Specification 663,231. In a modification, Fig. 2 (not shown), the capacitor 35 is included in a " bootstrap " integrator similar to the one shown in Fig. 3 (see below); valve 37 may then be an ordinary triode. Second embodiment. As shown in Fig. 3, a ship's log 1 is employed of the type used in the first embodiment, a D.C. voltage proportional to the speed of the ship being produced across a smoothing capacitor 209 which is momentarily connected to a capacitor 205 (charged from a constant voltage source 202) by a contact 201A of a relay 201 each time the log 1 emits a pulse. The speed voltage across capacitor 209 is applied through an amplifier 210 to a compass-controlled sine-cosine potentiometer 211 and the cosine component is applied through a contact 221 to the upper electrode of a storage capacitor 223 whose lower electrode is connected through a contact 222 to the cosine output of a sine-cosine potentiometer 214 which is set manually in accordance with the drift direction, the D.C. voltage across the potentiometer 214 being set by a potentiomter 217 in accordance with the magnitude of the drift. The changeover contacts 221, 222 and operated periodically by a relay 251 controlled by a periodic voltage source 250 so that the voltage across capacitor 223 which is proportional to the N-S component of the true speed is applied intermittently to a bootstrap integrator comprising valves 107, 105 and an integrating capacitor 35. The output from the integrator is thus proportional to the N-S component of the ship's position and is applied to a Y-deflection coil 42 through an amplifier 237. The periodicity of the source 250 is set in accordance with the range of the P.P.I. display so that the scale of the position shift is equal to that of the display. Reference has been directed by the Comptroller to Specification 599,889, [Group XL].