Patent GB-366989-A (GB)
Title: Improvements in and relating to radio telegraphic direction finding and the like
IPC: G01S3/42
Filed: 1930-08-05
Abstract: 366,989. Electric signalling systems. WATT, R. A. W., BELL, L. H. BAINBRIDGE-, Radio Research Station, Department of Scientific & Industrial Research, and CHAFFER, C., Admiralty Compass Observatory, Ditton Park, both in Slough. Aug. 5, 1930, Nos. 23479/30 and 13925/31. [Class 40 (i).] Relates to indicating devices of the kind in which the ionic beam from a cathode-ray oscillograph is utilized to indicate the relative strength of applied electric or magnetic fields of force, as for instance in the direct-reading radiogoniometer described in Specifications 252,263 and 267,575, [both in Class 40 (v), Wireless signalling &c.]. The invention consists in the provision of means whereby the fields of force applied to the electrodes of the cathode-ray tube produce relative motion between the electrode system and the ionic beam. Associated amplifying devices and a motor are then utilized to rotate the oscillograph tube, so that the initial datum or zero setting of the beam is automatically maintained, the resulting angular movement of the electrode system gives a direct indication of the deflection of the ionic beam under the applied forces. The reading may be repeated at a distant point. The arrangement may also be used as a " compass " device to indicate deviation from a given course ; or as a bank or tilt indicator for aircraft ; or for the control of distant apparatus through " follow-up " or repeater devices. As shown in Fig. 1, a cathode-ray oscillograph 1, mounted on a rotatable platform 2, contains two electrodes 3, 4, coupled through amplifiers 5, 6 to a current indicator 7, which measures the sum of the currents flowing into the amplifiers and is connected to the anode of the oscillograph by a wire 8. The amplifiers operate a differential relay 9 which causes current from a battery 13 to drive the motor 16 in one direction or the other in order to rotate the platform on which the oscillograph tube is mounted through an angle equal to the displacement of the ionic beam 34. The movement of the platform 2 is transmitted through a gear 19 to a commutator 20 feeding current from a battery 21 to one or more coils 26, 27, 28. These determine the alignment of an armature 29 coupled to a pointer 30 which moves over a scale 31 to give a direct reading of the displacement of the oscillograph tube 1 as the spot 34, Fig. 3, formed by the ionic beam moves, say, from a position where it impinges equally over both electrodes 3, 4 to a position. Fig. 2, more to the left, in consequence of the movement of the craft carrying the installation. The action of the amplifiers 5, 6 and the motor 16 tends to maintain the spot 34 midway between the electrodes 3, 4 and the resulting rotation of the platform 2 is indicated by the pointer 31. In another arrangement the beam impinges upon a fluorescent screen divided by a central opaque wall with light-sensitive cells on each side arranged to operate the driving motor in one direction or the other until the illumination is equal on both sides of the wall. To secure the advantage of amplifying rapidly alternating as distinct from a slowly fluctuating current, the ionic beam may be accelerated by a pulsating voltage ; or an alternating field may be applied across the interelectrode gap ; or the electrodes may be provided with insulated strips or squares of a width comparable with the cross section of the beam ; or rotating shutters may be interposed in the path of light. The electrodes may determine angular co-ordinates referred to the axis of rotation of the tube, or they may be shaped to give a radial co-ordinate by arranging that the current drawn from the beam varies according to a linear law as it traverses the electrode area. In applying the oscillograph as a compass or " bearings " indicator, or as a bank or tilt indicator for aircraft, the effect of the earth's magnetic field on the ionic beam is utilized. For a given magnetic dip, the beam will trace out a circular track on the fluorescent screen as the tube is rotated about a vertical axis. This circle simulates a compass " card " on which movement of the fluorescent spot indicates a change in orientation of the craft. If the spot moves outside or inside this circle it shows that the tube is not vertical, thus serving as an indication of " bank " or " tilt " on an aeroplane. Fig. 6 shows an arrangement for applying a local control field as an alternative to the earth's magnetic field for constraining the beam to a constant position in space. The electrodes and control coils are connected as follows : 44 to coils 48, 49 ; 45 to coils 50, 51 ; 46 to coils 52, 53 ; and 47 to coils 54, 55. The free ends of the coils are connected by wire 56 to the anode of the oscillograph. The armatures 57, 58 according to their positions cause the motors 65, 66 to rotate in one direction or the other so as to vary the settings of tappings 71, 72 on potentiometers 73, 74 thereby determining the currents flowing from batteries 75, 76 through the deflecting coils 77, 77a, 78, 78a. Should the spot 34 move upwards from the centre point of the four electrodes 44 .. 47 as shown in Fig. 6, motor 65 will cause current to flow in coils 77, 77a so as to bring the spot 34 back again. The resulting change in current due to the displacement of the potentiometer tapping 71 is indicated by an instrument 80. Similarly an initial displacement of the spot sidewise will be followed by a movement of the potentiometer tapping 72 and a corresponding indication in the meter 79. The readings of the meters 79, 80 are shown by the pointers 82, 83, Fig. 7, their point of intersection indicating the restoring forces applied to the beam, and therefore its unrestored position. When the installation is used as an aircraft compass the locus of the point of intersection will be a circle in the absence of " pitching " or " banking."