Patent GB-594288-A (GB)
Title: Improvement in radio beacon systems
IPC: G01S1/24
Filed: 1944-06-02
Abstract: 594,288. Radio navigation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 2, 1944, No. 10685. Convention date, Nov. 2, 1942. [Class 40 (v)] In a course and position indicating system, a mobile receiver is responsive to the simultaneous reception of pulses from two spaced transmitters to give an "on course indication and to the reception of a pulse from another fixed transmitter simultaneously with the other pulses to give a " position " indication. Fig. 1 shows three fixed transmitters X, Y and Z from which pulses are radiated at a given recurrence frequency. The pulses from X and Y are emitted simultaneously and will arrive simultaneously at a mobile receiver on the course line AB. The emission of pulses from Z is delayed whereby simultaneous reception of all three pulses will occur only at a specific point P on AB, the distance along AB depending on the aforesaid delay. In the mobile equipment shown in Fig. 4 the trains of pulses from transmitters X and Y are received by receivers X' and Y<1> and applied to the control grids of a coincidence valve 1. On the simultaneous reception of pulses, the valve 1 conducts and operates an " on course " indicator 11. Part of the output of valve 1 is applied through a phase inverter 14 to one of the control grids of a second coincidence valve 15 which is thereby gated. Pulses from the transmitter Z are received by a receiver Z<1> and applied to the other control grid of the valve 15. On the simultaneous reception of a gating pulse and a pulse from the transmitter Z, the valve 15 conducts and operates a " position " indicator 17. In the arrangement shown in Fig. 8a, the three received pulses are separately displayed on a cathode-ray tube 23. The output of receiver X' synchronises a sawtooth generator 21 with alternate pulses of the train and the output of the generator 21 is applied to the horizontal deflection circuit of the tube 23. The output of the generator 21 is also applied to a 3 to 1 frequency divider 33 adapted to produce an output having a stepped wave form 35. The frequency divider 33 may be of the type described in Specification 471,731. The output of the frequency divider 33 is applied to the vertical deflection circuit of the tube 23 to provide three verticallyspaced traces, and also to a gating-pulse generator 37 adapted to provide three square wave-outputs 39, 41 and 43, each corresponding in time with one of the steps of the wave 35. The square wave outputs are applied to three coincidence devices 45, 47 and 49 so as to gate them in synchronism with the formation of the three traces on the cathode-ray tube. The outputs of the receivers X<1>, Y<1> and Z<1> are applied also to the coincidence devices 45, 47 and 49 and the outputs of the latter are applied to the horizontal deflection circuit of the tube 23. A phase inverter 46 may be switched into the output circuit of device 49 whereby the pulse showing arrival at destination is inverted. The gating-pulse generator 37 for providing the three square wave outputs 39, 41 and 43 comprises three valves 34, 40 and 42, Fig. 8b, each having a load resistance in both its anode and its cathode lead and thus providing two outputs which are inverted with respect to one another. The outputs of the valve 34 are applied to the grids of the valves 40 and 42 which operate as peak amplifiers. The voltages across the cathode load resistances of the valves 40, 42, provide the wave forms 39, 43 respectively. The anode outputs of the valves 40, 42 are applied to a fourth valve 44 the two wave forms combining to provide cut-off bias. Valve 44 thus conducts only when the bias voltages are " off and provides an output corresponding to wave form 41. In another arrangement, Fig. 5 (not shown) the pulses are indicated on a single trace. In a further arrangement, Fig. 13, the time base of the cathode-ray tube produces alternate horizontal and vertical sweeps. The saw-tooth generator 21 is synchronised on alternate pulses in the output of the receiver X<1> and its output gates two coincidence devices 53 and 55 and is also applied to a two to one counter 33. The counter 33 provides a synchronised square wave output 65 which is fed directly to the coincidence device 53 and through a phase inverter 51 to the coincidence device 55. The devices 53, 55 therefore conduct alternately, providing outputs 69, 71 which are fed to the Y-plates and X-plates respectively of the cathode-ray tube 23. In order to cause the vertical and horizontal traces to cross at their centres, the square waves 65 and 67 are also used as shift voltages and are added through phase inverters 59 and 57 to the outputs of the devices 53 and 55. The receivers Y<1> and Z are normally connected through switches 61 and 63 directly to the X- plates and Y-plates of the cathode-ray tube, the receiver X<1> not being directly connected to the tube. In this position of the switches, the position of a pulse on the horizontal trace with respect to the vertical trace gives an indication whether the mobile receiving equipment is on course or to the right or left of the course, and the position of a pulse on the vertical trace with respect to the horizontal trace indicates when the craft is approaching the given destination. The indication shown in Fig. 18 shows that the destination has been reached. In the other position of the switches 61and 63, the receiver X<1> alone is connected through to both X-plates and Y-plates for the purpose of adjustment of the equipment.