Patent GB-672782-A (GB)
Title: Sound indicator for indicating hits scored with weapons, especially aircraft weapons
IPC: F41J5/06
Filed: 1949-02-24
Abstract: 672,782. Controlling and actuating by sounds. SVENSKA AEROPLAN AKTIEBOLAGET. Feb. 24, 1949. [Feb. 24, 1948 ; March 19, 1948] Nos. 5090/49 and 5091/49. Addition to 652,032. Class 118 (ii). [Also in Group X] The arrangement claimed in the parent Specification for indicating when hits are scored on a flying target is modified to take account of the different ranges at which firing takes place or of the different calibre ammunition employed or to locate the point at which a shot passed the target. A shot arriving from a long range will be travelling more slowly and so give. rise to a weaker signal, but the frequency of the sound due to a bow-wave is proportional to the speed of the projectile. The sound-sensitive device employed is therefore a microphone in conjunction with an electrical filter of a falling amplitude-frequency characteristic. In this way projectiles fired at all ranges give rise to substantially the same strength of signal. In order to compensate for the different calibre projectiles in use a filter having the characteristic of Fig. 7 may be employed. In this filter the pass characteristic is, arranged to have substantially linear downward slopes over the frequency ranges corresponding to calibres of, say, 40, 20, 13 and 8 mm. respectively. The increased amplitude of the peaks of higher frequency (or lower calibre) compensate for the weaker bow-waves generated in these frequency bands. It is stated that the electrical filters may be replaced or supplemented by suitable acoustic filters placed before the microphone. If the 'output of the microphone is applied to the grids of a number of electronic tubes with suitably graded grid biases then the nearness of a shot will be indicated by the number of tubes which conduct, and hence operate corresponding indicating devices. Alternatively, the output of the microphone may be applied to a single tube whose anode current is indicated on an ammeter and is a measure of the amplitude of the received signal and hence of the nearness of the shot. In order to indicate the approximate position of a shot at the nearest point of its trajectory, two microphones 71, 57 (Fig. 11) may be arranged in the line of flight and whether the microphone 57 or 71 or both operate their respective indicators 59, 58 is an indication of whether the shot passed in the right-hand, left-hand, or central zone respectively in Fig. 11. A similar arrangement is shown in Fig. 12 (not shown) using one omni-directional and two uni-directional microphones. With three omni-directional microphones arranged in a triangle and each connected to a current measuring electron-tube and ammeter the meter readings may be plotted and the exact location of the shot deduced, Fig. 10 (not shown). In order to reduce the number of conductors required in the towing cable when two microphones are used, one microphone is arranged to give rise to a uni-directional output in one direction and the other microphone in the other direction. Figs. 13, 15 (not shown) illustrate circuits employing rectifiers for obtaining this.result.