658,745. Radiolocation. WESTERN ELECTRIC CO., Inc. Oct. 22, 1947, No. 28262. Convention date, Oct. 23, 1946. [Class 40 (vii)] In a radar system, the aerial system produces a narrow-angle nodding beam which cyclically occupies positions on each side of the nodding plane, and echo signals are presented on a cathode-ray tube screen, the echoes from each target being shown as two closely adjacent indications corresponding respectively to echoes received from each side of the nodding plane and distributed along one dimension of the screen in accordance with the appropriate nodding angular position of the beam. The invention is applied to a gun-laying radar system comprising a conically scanning transmitting-receiving aerial which is mounted to rotate in azimuth with the gun system and involving two modes of operation: (1) the "search" operation during which the aerial nods vertically about a mean position corresponding to the direction in which the gun system is aimed so that a particular target may be selected and the aerial and gun systems directed thereto; (2) the "track" operation during which the aerial nodding ceases so that the system may locate the target with an improved accuracy, and information concerning the position and movement of the target is fed to a system controlling the relative movement of the gun and aerial system in order to direct the gun system at a predicted future position of the target. The aerial 11 comprises a reflector and an eccentrically mounted primary radiating system of the type described in Specification 588,159, and rotating continuously about the axis of the reflector. The aerial 11 is mounted in gimbals 16 above the guns 10 and is normally directed parallel to the guns. Pulses generated at 29 are supplied by the transmitter 31 to the aerial system and are also applied to the sweepgenerating circuits 40 and 42. Echo signals are passed by T-R box 33 and units 34, 35 and 36 to the appropriate electrodes of the cathode-ray tubes 13 and 14. Cathode-ray tube 14 provides a type-A display and tube 13 provides, when the aerial is nodding, a range-elevation display, the vertical deflection of the tube being controlled by the potentiometer 18 which is actuated in synchronism with the nodding motion. The movement of the aerial and guns in azimuth and elevation (apart from the nodding) is controlled by a director 12. The director operator moves the director in accordance with the position of a spot 74 on the screen of the cathode-ray tube 15 which is controlled by signals sent from apparatus associated with the tubes 13 and 14. Search operation. The switch 25 is placed in the position shown whereupon the aerial 11 commences its nodding motion. The amplitude of the nodding motion may be controlled by a switch 24. Echo signals are displayed as shown on tubes 13 and 14, each echo giving rise on the tube 13 to a double indication, the relative lengths of the two traces indicating the misalignment in azimuth between the reflecting object and aerial directivity. Misalignment in elevation is indicated by the relative positions of the echo signal and cross-hair 77. The operator turns the knobs 75, 76 of the azimuth and elevation-units 21 and 22 in accordance with this mis-alignment, the units 21 and 22 being coupled via switch 25 to the cathode-ray tube 15 to displace the spot 74 in accordance with the movement of the knobs. By a suitable movement of the director the director operator is able to recentre the spot. When the two traces of the double indication on tube 13 are of equal length and are situated on the cross-hair 77, and the spot 74 is central on the tube 15, the guns are accurately pointed at the target. A further operator rotates the knob 81 of range unit 23, thereby controlling the timing of a range-marker pulse generated at 44, until the step 82 is set upon the selected echo on the tube 14. The range marker is also displayed on the tube 13 as a pair of lines 80. Track operation. When the search operation is completed, switch 25 is depressed, whereupon the aerial nodding ceases. The echo signals are applied to unit 87, wherein the phase of the modulation envelope due to the conical scan is compared with that of a reference voltage generated in two-phase generator 17 which is coupled to the motor for producing the conical scan. The output of unit 87 is coupled to the cathode-ray tube 15 via switch 25 to control the position of the spot 74, which the director operator maintains at the centre of the screen by suitably moving the director. Signals representing range and rate of change of range are fed from unit 23 to a computer unit 19 of the director 12. The unit 19 so modifies the coupling between the director, the aerial and the guns, in accordance with the signals applied thereto, that while the director and aerial system remain pointed at the target, the guns are trained on a predicted future position of the target. Details of display on cathode-ray tube 13. A reference voltage from the generator 17 is applied to square-wave generator 45 which produces a small-amplitude square wave synchronized with the conical scan. This is applied to the horizontal deflecting plates of the cathode-ray tube so that indications due to echo signals received during one half of the aerial scan are displaced from those due to signals received during the other half, the two indications being of equal brilliance and length when the target is illuminated equally by the transmitted beam during each half of the aerial scan. By a comparison of the lengths of the indications the operator can determine the direction of the misalignment and rotate knob 75 accordingly. However, should the target be so far off the axis of the beam that it is illuminated during one half of the scan only, simple inspection cannot determine the direction of the misalignment. To enable the determination to be made under these conditions, motor 27, which is synchronized with the conical scan by means of generator 17, rotates the two-colour filter disc 26 in front of the screen of the tube. By suitably choosing the colours of the disc in relation to the colours of the initial response and the after-glow of tube 13, the indications produced in the two halves of the aerial rotation will be seen in different colours. When measuring the misalignment in elevation the knob 76 is depressed and turned, whereby the cross-hair 77 may be moved into coincidence with the selected target. The director operator's display is affected accordingly and he is able to make the necessary adjustment. On releasing the knob 76, the cross-hair once more takes up its position at the centre of the screen.