Patent GB-586833-A (GB)
Title: Improvements in or relating to arrangements for locating objects by radio waves
IPC: G01S13/12
Filed: 1942-03-20
Abstract: 586,833. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd., CHATTERJEA, P. K., and HOUGHTON, L. W. March 20, 1942, No. 3758. [Class 40 (v)] In an obstacle locating' system in which trains of regularly repeated pulses of electromagnetic waves are derived from a saw-tooth relaxation oscillator, radiated, and received after reflection, means are provided for causing the reflected pulses to synchronise a saw-tooth relaxation oscillator. In the arrangement shown in Fig. 1 a saw-tooth relaxation oscillator 1 controls a pulse generator 2, which delivers the pulses to a radio transmitter 3 and transmitting aerial 4. Pulses reflected from the object are received on an aerial 5 connected to a receiver 6; amplified, and if necessary reshaped, in a pulse amplifier- 7, and returned to the oscillator 1 to control the saw-tooth waves generated. The period of the saw-tooth oscillations generated, in the absence of reflected pulses, is twice the time necessary for waves to reach the most distant object it is required to locate, and a short pulse is emitted at the moment of each fly-back stroke. When an object comes within the range of measurement a reflected pulse is received within a shorter time than the normal period of the oscillator and causes the fly-back stroke to be produced at that moment, the next pulse being simultaneously emitted from the generator 2. The oscillator thus generates oscillations of a higher frequency corresponding to the distance of the object. The output of the oscillator 1 is passed through a discriminator 8 which separates out the fundamental frequency and produces a continuous output voltage proportional thereto. This is measured on a voltmeter 9 calibrated in terms of distance. Since transmitted and reflected pulses occur at the-same time, a single aerial may serve both for transmitting and receiving. The effect of pulses. reflected from obstacles beyond the maximum range is eliminated by obtaining from the discriminator 8 a proportion of the output voltage, which is proportional to the oscillation frequency, amplifying or attenuating it in a device 15, and applying as a grid bias to the oscillator 1 in such a manner that the fly-back strokes initiated by the reflected pulses would just be prevented in the absence of the reflected pulses. Fig. 5 shows another arrangement including a saw-tooth oscillator 1, pulse generator 2, radio transmitter 3, and aerial 4 arranged as in Fig. 1. Reflected pulses received on the aerial 5 are demodulated in the receiver 6 and applied to synchronise another saw-tooth oscillator 10. An inverting device 11, which may comprise an amplifying valve, inverts the saw-tooth oscillations generated in the oscillator 1 and applies them to a mixer 12 where they are combined withoscillations at the output of the oscillator 10. The oscillations of the oscillator 10 are shown at e, Fig. 6, and the oscillations inverted by the inverter 11 are shown at f. After mixing the resultant shown by the curve g is obtained. These oscillations are applied to a device 13 which converts them into undirectional pulses which are measured on a voltmeter 14 calibrated in terms of distance. To maintain'stability when no reflected pulses are received a weak synchronising pulse is fed from the generator 2 to the generator 10 so that the curves e, f cancel each other and produce no pulses g. The sudden change of voltage at the terminals of the meter 14 when an obstacle comes within range may operate an alarm.