Patent GB-542634-A (GB)
Title: Apparatus for simultaneously measuring distances and directions of invisible objects from a movable or stationary spot
IPC: G01S7/10
Filed: 1939-10-16
Abstract: 542,634. Radio direction finding. ROST, H. F., and CLAESSON, P. H. E. Oct. 16, 1939, No. 27891. [Class 40 (v)] [Also in Group XXXVI] A system for simultaneously indicating the direction and distance of invisible objects includes a transmitter of frequency modulated radio waves, an automatically rotatable radio wave receiver, analysing means for determining the intervals between transmitted and received wave reflected from the objects to be located, means for indicating the direction of a reflected wave, and analysing means responsive to and proportional to the time interval between the transmitted and reflected wave to indicate the distance of the objects. In the apparatus shown in Fig. 1, a micro-wave radio transmitter 1, a frequency modulator 2, and detector 4 are mounted on a shaft 16, which carries slip rings 6, 7, 10, 11 and is rotated by a motor 19 through worm gear 17, 18. A second shaft 59 is driven synchronously with the shaft 16 by a motor 62 through worm gear 60, 61. Synchronism between the two shafts is ensured by soft iron toothed discs 65, 70 carried by the shafts 16, 59 rotating in the fields of coils 66, 67, 68, 69 supplied with single phase current. On the shaft 59 is mounted a frequency or phasedifference meter 46, the movable system of which carries a mirror 47 movable about a centre 48. The beat frequency current is passed through an automatically regulating amplifier 27 by which the amplitude of the output wave is kept constant. A second amplifier and rectifier 49 provides a high voltage for operating a Kerr-cell 51 which together with lenses 53, 56, Nicol prisms 54, 55, and a mirror 57, serves as a light relay controlling the light from a source 52 so that a beam of light is reflected on to the mirror 47 only when reflected waves are received. The parts 51...57 are mounted on the shaft 59. The light ray from the mirror 47 of the frequency meter falls on a fixed opaque or fluorescent screen 58. In a modification, Fig. 2, the indicating instrument is stationary, a similar Kerr-cell light valve being used. Diametrically opposite coils 86, 87 are connected in series with brushes 78, 79 engaging a resistance wire 77. A second pair of diametrically opposite coils 88, 89 are connected in series with brushes 80, 81 engaging a resistance wire 76. A bar magnet 90 is centrally suspended by silk threads 91 attached to an insulating ring 93. A mirror 92 is attached to and follows the movements of the bar magnet 90. The coils 86...89 attract or repel the lower end of the magnet 90, leaving the upper part to make corresponding movements with the attached mirror. The resistances 76, 77 are so arranged that the light beam 71 on a screen 58 indicates the direction of the transmitter 1 and receiver 4. The magnitude of the deflection of the beam 71 depends on the beat frequency and is determined by a device 72, comprising for example condensers, which passes more current at higher beat frequencies. In the instrument shown in Fig. 4 the shaft 16 is given a rotating back and forth motion by means of a pin 114 and slotted arm 115. A cathode ray oscillograph 102 has its deflecting plates 103, 104 connected through brushes 78...81 on resistances 76, 77 so that the direction of the beam indicates the direction of the reflecting obstacle. By means of a beatfrequency analyser 112 the distance to several obstacles one behind the other may be measured. A rotating condenser 113 of special 'shape is associated with the analyser 112 and continuously changes the wave adjustment so that all beat frequencies are analysed and registered. The motor 19 is arranged as a single phase converter, the resulting current being taken from slip-rings 24 for frequency modulation and also for continuously moving the oscillograph beam in straight lines from the centre to the edge of the fluorescent screen all through the scanning angle through which the transmitter and receiver are moved. By means of a beam trap 106 the beam is allowed to pass only when a reflected wave is received. Vertical scanning may be employed instead of or in addition to horizontal scanning. A linear time-base oscillator may be used for modulation and also for the variation of the wave analyser 112 instead of the variable condenser 113. The linear time-base oscillator may further be used for the direction of the cathode-ray beam from the centre to the edge of the fluorescent screen.