GB581169A - Improvements relating to measurement of distances of obstacles by radio electric waves - Google Patents

Abstract

581,169. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). Dec. 26, 1941, No. 16698. [Class 40 (v)] In a system in which the transmitted wave is frequency modulated and the reflected wave is heterodyned with the contemporaneous transmitted wave, the beat frequency is measured by a frequency analyser that permits simultaneous or successive measurement of several frequencies corresponding to different obstacles. The transmitter consists of an oscillator 2 feeding a directive autenna 1 and may operate at a wave length of 17 cm. modulated through an amplifier 4 by a frequency varying linearly from 18 to 20 megacycles. The modulation oscillator 31 comprises a rotating condenser driven by a motor 38. The receiver system comprises a receiving autenna 6 which feeds a detector 8 tuned to the wave length of 17 cm., the frequency band width permitting reception of the modulation band from 18 to 20 megacycles. The detector 8 is followed by a selective amplifier 9 and a modulator 11 which also receives energy tapped from the amplifier 4 by way of an amplifier 10. The beat frequency, which is proportional to the distance of the reflecting object, is obtained at the output of the modulator 11 and is passed through a low pass filter 12 to a low frequency amplifier 13. The output of this amplifier is passed to a frequency analyser comprising a regulation attenuator 15 followed by a separator 16 which feeds two circuits, the upper manually controlled reading circuit and the lower automatic scanning device. The latter comprises a modulator 23 which is fed from a variable frequency heterodyne oscillator 27 and by the frequency to be analysed. The frequency of the oscillator 27 is continuously varied by means of a rotating variable condenser 33. The output of the modulator 23 is fed via a selective amplifier 24 to one pair of plates of a cathode rayoscillograph 25, the other pair of plates of which is connected to a scanning circuit 29 controlled by the contacts of a switch 35 mounted on the same shaft as the condenser 33. A circuit 28 controlled by a switch 34 on the condenser shaft suppresses the cathode beam so that it only exists while the frequency of the oscillator 27 is decreasing and is extinguished while this frequency is increasing its positive value for the next scanning. Switches 36, 37 close circuits at given moments of the condenser variation cycle so as to produce on the oscillograph screen a series of dashes to constitute a distance scale. One or more obstacles corresponding to one or more beat frequencies may thereby be detected and their distances read off on the scale of the oscillograph. For determining the distance of an object with greater precision a modulator 17 is fed from the separating circuit 16 and also from a manually controlled heterodyne oscillator 18. The output is passed via a selective amplifier 20 with a narrow pass band to a measuring instrument 22. The frequency of the oscillator 18 is varied to obtain a predetermined fixed frequency output, the oscillator frequency then being a measure of the beat frequency and therefore of the distance of the reflecting object and the instrument 22 giving an indication of the intensity of the reflected wave.