Patent GB-585568-A (GB)
Title: Improvements relating to arrangements for determining distances by reflection of electrical pulses
IPC: G01S13/10
Filed: 1941-12-19
Abstract: 585,568. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd., and BEATTY, W. A. Dec. 19, 1941, No. 16434. [Class 40 (v)] In distance measuring apparatus in which the time between the transmission of a pulse and the reception of the reflected pulse is measured the transmitted and reflected pulses are utilised to establish solid pulses, the duration of which depends upon the time elapsing between transmission and reception, and these solid pulses are utilised to determine the distance. A signal generator generates a waveform 22, Fig. 3, from which are generated short pulses 23 coinciding with the peaks of the waveform. These pulses energize a transmitter which radiates corresponding pulses and also receives the pulses 24 after reflection from the object whose distance is to be measured. As shown, the time elapsed between the transmission of a pulse and the reception of the corresponding pulse is half the time interval between transmitted pulses. The pulses 23, 24 are utilised to establish a train of longer pulses 25 having a duration of half the repetition period. If this relationship does not hold, the pulses 25 control the frequency of the signal generator until it is attained. The frequency of the signal generator is then a measure of the required distance and the dial of the frequency adjusting element may be calibrated in terms of distance. The pulses 25 may be produced by applying the transmitted and received reflected pulses, one to each grid of a double-stability trigger circuit, and may be applied to operate auxiliary apparatus. In an alternative arrangement the waveform 22 remains at a constant frequency, each cycle of which has a duration longer than twice the longest elapsed time likely to be experienced. The pulses 25 are then built up adding the transmitted and received pulses, which will overlap by varying amounts, and the overlapping portion or the full resultant pulse will have different durations and can be integrated to give directly a measure of the distance. If the repetition frequency of the pulses is variable the transmitted and received pulses may be employed to establish the longer pulses, which may then be integrated and the product balanced against a constant current or voltage and the differential current or voltage applied to control the frequency of the wave from which the pulses are produced. In order to prevent false readings due to nearby objects such as the balloon barrage a train of pulses 29 is generated having the leading edges coinciding with the pulses 23 and a duration corresponding to the height of the balloon barrage. These pulses are used to block one or more circuits in the receiving system so that the apparatus is rendered insensitive to reflections from objects below a predetermined height. In order to follow the path of a moving object four antennµ may be arranged at the corners of a square, with a fifth antenna in the centre. The central antenna is arranged to transmit pulses which are reflected from the object and received on the four corner antennµ. The received signals from diagonally opposite antennµ are balanced against each other and the system is manually rotated until the difference signal is zero, the central antenna then pointing 'directly at the object. The arrangements are then switched over to automatic mechanism under the control of the difference signals from the two pairs of antennµ. For indicating when the correct frequency of the transmitted pulse has been obtained, a waveform 30, Fig. 4, of potentially variable frequency is utilised to control the generation of transmitted pulses 33 coinciding with the positive peaks of the waveform 30. When the period of the waveform 30 is equal to twice the elapsed time of the reflection pulses 34 from the moving object, these pulses coincide with the negative peaks 32. The waveform 30 also establishes the trace 35 on the screen of a cathode ray tube 36, Fig. 5, the left-hand side of the trace corresponding to the positive peak of the waveform 30. The reflected pulses 34 deflect the beam transversely, giving a trace 37 at the extreme right-hand end of the trace 35 when the waveform 30 has a period equal to twice the elapsed time. In a modification, two waveforms 39, 40, Fig. 6, are established, the waveform 40 having twice the frequency of the waveform 39. These two waveforms establish a looped trace 41, Fig. 7, on the screen. When the frequency of the waveform 39 is such that its period is four times the elapsed time, a vertical trace 45 occurs at the cross-over of the trace 41.. Specifications 579,118, [Group XXXVIII], and 583,511 are referred to.