GB573900A - Improvements in or relating to signalling systems - Google Patents

Abstract

573,900. Signalling by light beams. FFENNELL, H. S. MOLYNEUX-, TAPP, E. T. J., CHARLTON, F. G., and VACUUM-SCIENCE PRODUCTS, Ltd. Aug. 25, 1941, No. 10842. [Class 40 (iii)] In an apparatus for transmitting modulated light signals, the shutter device comprises a fixed shutter 16 having openings 9, Fig. 3, three times the width of the opaque portions 10, a movable signalling shutter 18 with similar openings and opaque portions, and a movable modulating shutter 14 with equal openings 24, Fig. 2, and opaque portions 23 of the size of the opaque portions of the other shutters, the arrangement being such that the signalling cannot be detected by the eye, but only by a correspondingly tuned receiver. As shown in Fig. 1, the shutters 14, 16, 18 are arranged in front of a lamp 20 situated at the focus of a parabolic reflector 19. The modulating shutter 14 is continuously rotated by an electric motor 11. The signalling shutter 18 is oscillated by a solenoid 6 through a lever 22 according to the signal to be sent. In a modification, Fig. 4 (not shown), the modulating shutter is oscillated. In another modification, Fig. 5 (not shown), the shutters are in the form of cylinders around a central lamp between suitably-shaped reflectors. The receiver may be mounted at 62, Fig. 6, to constitute one unit with a receiver aligned with the transmitter. The receiver comprises a lens 54 focusing the beam through an iris diaphragm 57 on to the - light-sensitive cathode of an electron multiplier 55 connected to a circuit 58 tuned to the modulation frequency of the light beam. To facilitate directing the unit in the desired direction, an adjustable mirror 59 is provided and may be swung into the path of the beam to deflect it to a ground glass focusing screen 60 at the bottom of a sighting tube 61. Cross wires are provided to help in centring the image on the ground glass. Alternatively, a telescopic system may be provided. An infrared screen may be associated with the transmitter, particularly when used for detecting ships at sea.