GB1410322A - Method and apparatus for the location of a source of electro magnetic radiation - Google Patents

Abstract

1410322 Direction finders FRANCE ARMED FORCES MINISTER OF 29 Sept 1970 46376/70 Heading H4D Apparatus for determining the azimuth and elevation angles of an electromagnetic radiation source, e.g. a nuclear explosion, comprises, Fig. 1, an encoder disc 1 of glass rotated by a motor 2 at a speed, e.g. 10 revolutions per sec., such that the period of rotation is less than the duration of the luminous source i to be detected. The disc 1 has two circular engraved tracks 4, 5, track 4 having a large number N of regularly spaced divisions and track 5 having a single engraved line, this line being radially aligned with one of the lines forming track 4. The tracks 4, 5 are read by a reader 6 comprising photo-diodes to produce pulses on conductors 8, 7 respectively. Thus, each division on track 4 produces a pulse a and the single division on track 5 produces a pulse b, these pulses being applied to an electronic logic system 17. An optical system 9 for receiving the luminous source i is rotated with the disc 1 and comprises an objective 11 which focuses the luminous flux on to two non-parallel slits 12, 13 formed in a plate 14, slit 12 being the "azimuth" slit and slit 13 the "elevation" slit. A photo-electric detector 15, preferably a vacuum cell having a photo-emissive cathode, responds successively to the beams of luminous flux passing the slits 12, 13 to produce, respectively a pair of pulses C1, C2 for each revolution of the disc 1, these pulses also being fed to the logic system 17. Pulse b provides a datum pulse and the system 17 determines the azimuth angle by counting the number of pulses a over the time period g extending to the commencement of pulse C1. The elevation angle is determined by counting the number of pulses a over the time period S between the pulses C1, C2. This is because, as shown in Fig. 3, the image i moves along a horizontal line x across the slits 12, 13 and as the elevation angle increases the traverse line moves from x2 to x1 and the interval S between the pulses C1, C2 correspondingly increases. The angular diameter of the source i may be determined by counting the pulses a over the period d corresponding to the width of pulse C1. An actual embodiment of the encoder 1 and optical system 9 is described with reference to Fig. 2 (not shown). The logic system 17 is described in detail with reference to Fig. 4 (not shown) and a modified logic system for detecting two luminous sources per revolution of the encoder 1 is described with reference to Fig. 5 (not shown). The slits 12, 13 may have alternative shapes as shown in Figs. 7-10. According to another modification (Fig. 11, not shown) the slits 12, 13 are formed by two bundles of light guides.