Patent GB-599889-A (GB)
Title: Improvements in radar navigating apparatus
IPC: G01S7/24
Filed: 1945-10-15
Abstract: 599,889. Radiolocation. THOMPSON F. C. Oct. 15, 1945, No. 26946. [Class 40 (v) In a pulse radar system carried by a moving craft wherein the echo signals are displayed on a cathode ray tube to give a maplike indication (e.g. a P.P.I.), the drift of the display across the screen of the cathode ray tube due to the motion of the craft is arrested by applying shift voltages varying with the co-ordinates of the craft, to the cathode ray tube. In the embodiment of the invention for use in aircraft, known means produce rates of rotation proportional to the components of the airspeed, these rotations being transmitted to the motors M, MA upon the operation of switch SX with the consequent closing of the relay contacts x1, x2, x3, x4, x5. The motor M rotates the arm of the potentiometer P in accordance with the East-West component of the distance travelled. The motor MA similarly drives potentiometer PA to measure the North-South component. To correct for windspeed the potentiometer PW is used. This is driven at a constant speed by ratchet motor MW, the two potentiometer arms moving in opposite directions and the output being applied across potentiometers VR2, VR3. The arms of these potentiometers are set according to the components of the windspeed so that the output voltages are a measure of the product of the windspeed component and time. Potentiometers VR4, VR5 are used for applying manually controlled shift voltages to the display. The voltages representative of the distance travelled in the East-West direction, the correction due to the wind in that direction and the horizontal shift voltage are all combined in a resistance network, the output of which is at 2. A similar output dependent on the North-South components is delivered at 2A, these voltages being used to control the time base circuits. When any one of the potentiometer arms approaches the end of its track, a cam is operated to light a lamp L. Shortly afterwards a further contact is closed to bring an interrupter m into operation so that the ratchet motor MW is operated more rapidly than before and the arms of potentiometer PW, are thus brought rapidly to the zero position. Also clutches C, CA, are released so that the spring loaded devices D, DA restore the arms of the potentiometers P, PA to the zero position. When these operations are completed and the neutral conditions of the circuit have been restored, the display having " jumped " to a position showing the craft once more at or near the centre of the screen, the clutches are re-engaged and the interrupter circuit opened. The stabilizing operation them commences afresh. Time-base circuits. The voltage from point 2 is applied to the grid of valve V11 which is cut off during the time-base stroke by a negative pulse from point 1. During the waiting period between strokes, however, the voltage at 2 controls the anode voltage V11 and thus that of the Miller time-base valve V12 so that the voltage at which the time-base stroke commences varies in accordance with the distance travelled, and the trace is shifted accordingly. A similar time-base circuit applied to the Y-plates of the cathode ray tube is controlled by the output from point 2A. Outputs varying sinusoidally with the aerial rotation and delivered from a sine potentiometer (not shown) are applied to the grids of the time-base valves so the time-base strokes are rotated to give a P.P.I. display. If the windspeed is not known, it may be measured with this apparatus by adjusting the arms of the potentiometers VR2, VR3 until the display becomes stationary, the components of the windspeed then being indicated by the potentiometer settings.