600,313. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd. May 26, 1944, No. 10303. Convention date, May 29, 1943. [Class 40 (vii)] In a radio system for determining the location of an obstacle by transmitted pulses and received echo pulses, the beam of a cathoderay oscillograph is arranged to scan at least two trace lines on which are imposed alternately indications of the transmitted and received pulses, the indications of a transmitted impulse and an echo impulse on one line extending in an opposite direction from those on a second line, and means is provided for retarding the scanning control until the impulse indications on the two lines are in alignment to obtain a zero-distance indication, said scanning 'control being further adjustable until the echo pulse indications are in alignment so that the adjustment relative to the zero indication corresponds to the distance of the obstacle. The arrangement includes a pair of coplanar direction-finding antennas which are alternately connected to the receiver for successively transmitted impulses and are adjustable until the oppositely directed echo impulses on the two trace lines are equal in amplitude to indicate a direction component, e.g. elevation or azimuth, of the obstacle. Impulses transmitted from antenna 12 and reflected from the object 17 are received by aerials 21, 22 and 23, 24 of an antenna system 20 which is adjusted in elevation and azimuth by motors 26, 27 through control devices 30, 34. A blocking device 45 synchronised by a circuit 14 allows alternate impulses received by the aerials 21, 22 to pass to the receiver 52 from which they are fed to an inverting and mixing circuit 53, described in detail in connection with Fig. 2, in which they are combined with a square wave 57 produced by a generator 56 under control of the generator 14 and an adjustable delay circuit 100. The impulses Y1, Y2 received by aerials 23, 24 pass through a blocking device 46 to a receiver 82 and mixing circuit 83, similar to the circuit 53, and fed with a square wave from the generator 56. The outputs from circuits 53, 83 indicated at 59, 59a are applied to circuits 60, 84 which are fed with a saw-tooth voltage 62 and blocking voltages 66, 67 of square wave form having a frequency one half that of square wave 57-as indicated in Fig. 3 for the circuit 60. The output from circuits 60, 84 indicated at 76, 76a, Figs. 1, 3, are applied to the plates 91, 92 and 93, 94 respectively of a cathode-ray tube 95, the sawtooth portions 62a, 62b moving the beam horizontally and vertically and the square-wave portions 57a, 57b combining with the saw tooth portions to produce a rectangular trace with inwardly directed markings corresponding to the impulses X1, X2, Y3, Y4 and to the reflected echo pulses EX1, EX2, EY3, EY4. The receivers 52, 82 are adjusted by controls 52a, 82a to make the impulses X1 and X2 and Y3 and Y4 equal on the screen 95 and the device 101 is adjusted so that the impulses X1, X2 and Y3, Y4 are in alignment thus providing a zero distance indication on the scale 102. The control 103 is then operated to bring the reflected impulses EX1 and EX2 and EY3 and EY4 into alignment, and the reading on the scale 102 indicates the distance of the object. The impulses X1, X2, Y3, Y4 may be eliminated by a circuit as described in Specification 592,346 when elevation and azimuth are being determined. The traces of the pulses EX1, EX2 and EY3, EY4 are suitably amplified by controls 52a, 82a and the angle of elevation obtained by the setting of control 30, so that the amplitudes of the pulses EX1 and EX2 are equal on the screen. The azimuth bearing is similarly obtained by the shifting of the antenna so that the traces EY3 and EY4 are equal on the screen, the indication being read from a scale 36 of control device 34. The inverting and mixing circuit, Fig. 2, comprises a valve V1 to which impulses X1, X2 .. EX1, EX2 .., indicated at 15, are applied and from which the output is fed to a valve V3 and also to valves V2 and V4. The square wave 57 is fed to a valve V5 whose output is fed partly to the output line 142 through a valve V9 and also to a valve V6 and the cathode of the valve V3 to eliminate from its output the impulses X2, EX2, X4, EX4 .... The output of the valve V5 is also applied to valves V7, V8 whose cathode is connected to the cathode of the valve V4 so that the impulses X1, EX1, X3, EX3 are blocked from the output of this valve. The combined output from the valves V3, V4 and V9 is indicated diagrammatically at 59, Figs. 1, 2. A similar output, indicated at 59a, Fig. 1, is derived from the circuit 83. The square wave generator 56 of Fig. 1 may be replaced by a combined squarewave and sinusoidal generator, Fig. 5 (not shown), to obtain wave-forms, Fig. 6 (not shown), which produce curved scanning lines on the screen of the cathode-ray tube, Figs. 7, 8 (not shown). The indications of distance, elevation and azimuth on the devices 101, 30, 34 may be transmitted over lines 115 to a predictor.