Patent GB-626660-A (GB)
Title: Improvements in or relating to navigation aiding radio systems
IPC: G01S13/87
Filed: 1946-08-30
Abstract: 626,660. Radio navigation; pulse selecting circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 30, 1946, No. 26232. Convention date, Feb. 28, 1941. [Classes 40 (vi) and 40 (vii)] In a radio-navigation system indicating the distance from an objective of a craft on a course between a fixed transponder station and the objective, wherein pulses radiated by the craft are returned by the fixed station and displayed on a cyclically repeated time base, synchronized with the transmission and having marked thereon a zero reference index, means adjusting the pulse transmission timing to bring the returned pulse indications into coincidence with the reference index when the craft has reached the objective are provided. If the craft is not on a given course two transponders spaced apart are required and alternate impulses or groups of impulses are radiated to one transponder and the remainder of the pulses to the other, the two sets being so adjusted in timing that the two returned pulse indications both coincide with the zero indication on the time base when the craft reaches its objective. In such a system, Fig. 1, an aircraft 11 flying to a distant objective 13 radiates pulses of energy of frequency F<1> which are received at responders A and B at spaced known locations and used to key pulse transmitters retransmitting at frequencies F<2> and F<3> respectively. On the craft the returned pulses are received and used to determine the distances from A and from B so that provided the distances from 13 to A and to B are known the craft may be navigated to it. A cathode-ray tube indicator is used with a circular time base trace and has a zero index deflection and also deflections on opposite sides of the trace marking the distances from A and from B. The whole trace may be equivalent to 125 miles. According to the invention the transmission of the pulses is delayed relative to the display system so that when the aircraft reaches the object the two distance markers on the display coincide with the zero index. For this purpose it is necessary to radiate alternately pulses timed to correspond to the distance of the object from A and, in the next time period, to correspond to its distance from B. Similar alternation of the receiver tuning is necessary. Switching is provided so that the display trace may be accelerated by 5 or 25 times to provide total trace lengths of 25 or 5 miles to enable the object to be accurately located. The craft receiver, Fig. 5, comprises a 93 Kc. oscillator 27 feeding a phase shifter 29 having two outputs whose phases are manually adjustable between 0 and 360 degrees feeding pulse generators 31 and 33 and a reference phase output feeding pulse generator 39. The pulses from this last generator are applied to a series of 5 to 1 dividing circuits 41, 43 and 45. The outputs of circuits 41, 43 and 45 are fed respectively to smoothing circuits 47, 49 and 51, and variable phase shifters 53, 55 and 57, which have two independent outputs and are similar to phase shifter 29. In addition to the adjustable phase outputs these phase shifters also have quadrature outputs which may be selected by switch 73 to provide a circular trace on cathode-ray tube 59 of whatever speed of rotation is required. The variable phase outputs from phase shifters 53, 55 and 57 are fed to pulse generators 61, 63, 65, 67, 69 and 71, as shown. The outputs of generators 61, 65 and 69 and also 33 are applied to a coincidence circuit 37, the output of which is a pulse occurring only when pulses from all the input circuits coincide. The pulses have flat tops and are of such shape (Fig. 10, not shown), that only one pulse from generator 33 is selected for each cycle of the lowest frequency and by adjustment of the phase shifters 29, 53, 55 and 57, this pulse may be delayed an amount corresponding to any desired distance relative to the time base reference zero. The output pulses are used to trigger transmitter 89 over switch 91. When switch 91 is on its other contact it derives similar triggering pulses from coincidence circuit 35, the pulses however having a different delay corresponding to the phase delay introduced into the outputs of variable phase shifters 29, 53, 55 and 57. The delay of pulses from circuit 37 is adjusted to correspond to the distance 13-A and that of those from 35 to 13-B. Receiver 97 has its hetrodyne oscillators switched in synchronism with switch 91 by switch 91a so as to receive return pulses from A and from B respectively during the periods of connection of circuits 37 and 35, and the output of the receiver is fed to central deflecting electrode 83 of the cathode-ray tube. In the case of B, return pulses switch 91b routes these through a phase reverser 96 so that they occur on the opposite side of the trace to the A pulse deflections. A reference phase output from terminal T222 of divider 45 is applied to pulse generator 87 the pulses from which gate pulses applied from generator 39 in circuit 85 and the output pulses are applied to the central deflecting electrode 83 of tube 59 to produce the zero reference mark. The separations between the A and B station return pulse deflections and this mark are dependent on the distance the craft has to go to reach object 13 at which all the deflections coincide. Circuit arrangements of a suitable phase shifter, frequency divider, coincidence circuit, and pulse generator, are described with reference to Figs. 6, 7, 8 and 9 (Figs. 6, 7 and 9, not shown). A circuit for producing a radial deflection of the trace in a cathode-ray tube not having a central deflecting electrode is also described in connection with Fig. 11 (not shown). Coincidence circuit. The pulses from the oscillator are applied to the cathode of a pentode valve and the three outputs of frequencies successively five times lower respectively to the grids. The valve passes current only when there is coincidence of application of pulses from each input.