Patent GB-887619-A (GB)
Title: Navigational aid systems
IPC: G01S1/02
Filed: 1958-12-29
Abstract: 887,619. Electric selective signalling systems. NELLI, P., and PUGNET, R. Dec. 29, 1958 [Dec. 25, 1957], No. 41874/58. Class 40 (1). [Also in Group XL (c)] Relates to a radio collision-warning system in which the probability of collision between two craft is evaluated on one craft by comparing the bearing of the other craft as determined by a radio direction-finder with the heading of the other craft as transmitted from that craft by radio. According to the present invention the heading is set manually into a coding device which generates a continuously-repeated electrical digital code signal train representing the heading and this signal is applied to a radio transmitter through a cyclically-operated switch, the relative duration of the on and off periods of the switch being adjustable. As described, this adjustment is effected in accordance with the speed of the craft but alternatively the speed may be indicated by (1) an audio modulation frequency, (2) the repetition rate of the identical heading signal trains in each transmission period, (3) the number of such trains in each transmission period, (4) the duration of the space between code signal elements in each train, or (5) the duration of the space between each signal train in a transmission period. For ships it is sufficient to discriminate between three speed ranges. Coding devices. The heading code signal train comprises two spaced groups of dots; the number of dots, i.e. one to four, in the first group specifies the bearing quadrant and the number of dots, i.e. zero to three, in the second group specifies the corresponding one of the four 22¢ degree sectors into which each quadrant is divided. The heading coder comprises a rotatable insulating concave drum 13, divided circumferentially into 16 longitudinal strips 14 corresponding to the 16 sectors, conductive strips 15 being inserted in each sector strip in accordance with the corresponding heading code. An insulating disc 16 is mounted on the shaft of a constant speed motor 17 so that the axis of the drum 13 is in the plane of the disc 16 and as the disc rotates pairs of contact brushes 18a, 18b mounted at its perimeter repeatedly scan the conductive strips 15 to produce a continuous train of heading-code groups of electrical pulses which are applied to the radio transmitter 35 via slip rings 19a, 20a, 20b and a cam-operated switch 34, Fig. 5 (not shown), driven by the motor 17, the mark/space ratio of the switch being determined by the form of the cam which is selected manually in accordance with the speed of the craft. A transparent compass rose 1 marked with the 16 sectors 2, Fig. 1 (not shown), is rigidly mounted on the drum shaft 6 and the required heading code is selected by rotating the drum by means of a knob 7 until the appropriate sector 11 is illuminated by a red lamp mounted below the compass rose, Fig. 2 (not shown). The contact brushes 18a, 18b are pivoted on the disc 16, Fig. 4 (not shown, so that they may be disengaged from the drum 13 when the latter is rotated. Alternatively the heading code pulses may be generated magnetically or photo-electrically.