Patent GB-617511-A (GB)
Title: Radio-location system
IPC: G01S13/00
Filed: 1946-02-01
Abstract: 617,511. Radiolocation. STANDARDTELEPHONES & CABLES, Ltd. Feb. 1, 1946, No. 3265. Convention date, Feb. 24, 1945. [Class 40 (vii)] In a radiolocation system for determining the position of a reflecting or re-radiating object, the transmitter and receiver are situated at different locations, means being provided for determining the parameters defining the triangle formed by the transmitter, receiver and object to be located and using them to actuate a, visual indicator to show the position of the object. In the system illustrated in Fig. 1, the transmitter 1 transmits a pulsed directional signal, the directivity of which rotates at 15 times per minute. The signal is received at a receiver upon the aircraft 2 by direct transmission and also after reflection from the object 3. The receiving system is illustrated in Fig. 3. The aerial 4 receives signals transmitted directly from 1 and is maintained directed towards the transmitter by means of the system 5, 6, 7, 8. The signals received on the two lobes of aerial 4 are selected alternately by the switching relay 5, passed to the receiver 6 and compared in the circuit 7 which energizes the motor 8 to maintain the signals received by each lobe equal. The shaft 9 is thus positioned according to the azimuth of the transmitter with respect to the axis of the aircraft, shown as the angle h, Fig. 1. The output of receiver 6 also controls the motor 14 by means of the circuit 16 which generates a synchronizing signal when the received signal is at its maximum amplitude so that the shaft 13 is -rotated in synchronism with the directive beam of the transmitter 1. The position of the shaft 13 is thus a measure of the angle b at any instant. The aerial 10 which receives the reflected signals is driven at 20 revs./sec., the position of the shaft 12 being a measure of the angle a<1> at any instant. The angle a is obtained by driving the stator of alternator 29 from the shaft 9 and the rotor from shaft 12 so that the instantaneous values of the output signals, taken to circuits 32, 33, 34 are dependent upon the instantaneous value of (a<1>+h), i.e. upon a. The output of alternator 30, which is dependent upon the instantaneous value of the angle b, is taken to the same circuits which feed into a computing circuit 28. The circuit 28 is also fed with a linearly increasing voltage from the sweep circuit 18 which is triggered by the pulses delivered from receiver 6. Thus, at the instant a reflected signal is received the voltage supplied by circuit 18 is a measure of the delay time and therefore of the quantity (A+BC). This factor together with the angles a, b is sufficient to determine the range B of the reflecting object from the receiver. The output of the circuit 28 which varies with the instantaneously corresponding value of the distance B is fed to the deflection circuit 21 to deflect the normally blanked cathode-ray beam radially by an amount proportional to B. The deflection circuit is also supplied with a signal from the alternator 24 which causes the beam to rotate in synchronism with the aerial 10. Thus, at the instant that a reflected pulse is received and a brightening pulse is applied from the receiver 19 to the grid of the cathode-ray tube, a visible indication is produced corresponding in position with that of the reflecting object. A P.P.I. display centred about the receiver is consequently presented on the screen of the cathode-ray tube. A display centred about the transmitter may be presented if desired. In this case the position of switch 25 is changed so that the output of alternator 27 controls the rotation of the display. The output of 27 which is differentially driven from shafts 9 and 13 is dependent upon the angle (b+h) which is the azimuth of the object 3 as seen from transmitter 1 with respect to the heading of the aircraft. The switch 35 is also changed over so that the output of the circuit 28 is made proportional to the corresponding value of the distance A. Fig. 4 (not shown) illustrates an alternative. system wherein rotary switches are coupled to the shafts 9, 12, 13, corresponding to those shown in Fig. 3, to vary resistance and capacitance values in accordance with the values of angles a and b. These elements form part of a sweep circuit and control the rate of increase of voltage therein in such a manner that at the instant of reception of a reflected signal the voltage reached is proportional to the distance B. This voltage provides the radial deflection of the cathode-ray tube which is here magnetically deflected. The rotational deflection is provided by rotating the deflecting yoke in synchronism with the aerial 10. Fig. 5 (not shown) illustrates a modification of the system of Fig. 4 wherein the reflected signal-receiving aerial comprises two selectively operable aerial systems directed in opposite directions, each aerial system being similar to the aerial 10 of Fig. 3. This system co-operates with a beacon transmitting two beams in opposite directions. A series of cams suitably coupled to the shafts 9, 12 and 13 switch the receiving aerials in such a manner that the operative directive pattern always intersects one of the beams from the transmitter. The cams also perform other switching operations to enable the correct display to be presented upon the cathode-ray tube. System employing two non-directive beacons, Figs. 9 and 10. In this system two omnidirectional beacons 64 and 65, spaced apart a known distance A, are used, beacon 64 transmitting a pulse-modulated signal. The transmissions from the beacons are distinguishable, e.g. they may radiate on different frequencies. The object 67 reflects signals from 64 which are then received on the aircraft 66 by the rapidly rotating aerial 101. The aircraft also receives transmissions direct from the beacons 64 and 65, these transmissions being received by the aerial systems 68, 69 and 78, 79 respectively. These signals then operate control circuits to position the shafts 77 and 87 so that the aerials 68, 69 and 78, 79 are directed towards the beacons 64 and 65 respectively. The shafts 77 and 87 are coupled into the differential gearing 88, the output shaft of which is positioned according to the angle a and controls the resistance 93 to be proportional to sin a. The compass 89 defines the north-direction N so that the output shaft of differential gear 90 measures the angle h<1> which is equal to the angle c if beacon 65 is arranged to be due north of beacon 64. The variable resistor 95 is controlled by the gear 90 to be proportional to sin c. Resistance 96 is made proportional to the fixed, known distance A and thus when the bridge is balanced the resistance 97 is, by the sine rule, proportional to the distance C. The motor 99, driven by the out-of-balance voltage, varies the resistance 97 until balance is achieved. The shaft 100 positioned according to the quantity C is, coupled into the sweep circuit 107. The differential gear 109 positions the shaft 110 according to the angle p, which quantity is also inserted into the sweep circuit. The sweep is initiated by the pulse signal received directly from the beacon 64 and fed to the circuit 107 over line 108. Thus, at the instant a reflected signal is received by the receiver 106 and is applied to the grid of the cathode-ray tube 104, the quantities C, p and (P + M - C) are known, these being sufficient to enable the circuit 107 to determine the quantity M. The output of circuit 107 is applied to the deflecting coil 103 which is rotated in synchronism with the aerial 101.