GB737519A - Improvements in or relating to radar display apparatus - Google Patents

Abstract

737,519. Radar displays. DECCA RECORD CO., Ltd. June 29, 1954 [June 29, 1953], No. 18028/53. Class 40 (7). A radar plan position indicator having a cathode-ray tube in which the centre of rotation of the rotating time base is displaced from the centre of the tube screen is provided with means for interrupting the offcentring voltage or current applied to the deflection means of the tube during the quiescent period of the timebase. The invention is of particular value in off-centred displays where the cathode-ray is electromagnetically deflected by the use of fixed deflector coils. In such a system a considerable reduction in the average deflection currents can be obtained with a corresponding simplification in the output stages of the time-base generators. In one embodiment of the invention in which a timebase generator of the type described in Specification 679,722 is used and provision is made for an off-centred bearing marker scan, each deflection coil 10 is in the anode circuit of an output valve 11. The grid of this valve is directly coupled through cathode follower 19 and amplifiers 18 and 17 to the cathodes of the valves in the four alternative control circuits 12, 13, 14 and 15. The cathode of valve 11 is coupled back to the grids of the control circuit valves. Control pulses are applied at G1, G2, G3 and G4 to render the control circuits effective as required, not more than one of them being in use at any one time. None of them is effective in the quiescent period and the beam rests in the centre of the tube. If a short positive pulse is applied at G1 control circuit 12 with its purely resistive feed-back coupling 31 is effective to cause the beam to be off-centred to a new zero whose position is dependent on applied voltage VI. Immediately following the short pulse at G1 a longer pulse at G4 is applied to render the control circuit 15 effective. The feed-back elements of this circuit include a resistor 24 and capacitor 22 so that there is a saw-tooth scanning current developed whose slope is dependent on voltage V4. At the end of the scan the pulse at G4 is terminated and the tube beam returns to its central rest position. Control circuit 13 is similar to circuit 12 and 14 similar to 15; they are controlled in the same way by a short pulse at G2 followed by a longer pulse at G3. The circuits 12 and 15 may be used for the production of a bearing marker scan from a required off-centred position and circuits 13 and 14 for the production of the off-centred display scan. Specification 744,640 is referred to.