Patent GB-1039526-A (GB)
Title: Position indicator
Inventor: SOTHCOTT PETER
IPC: G01S5/04
Filed: 1963-07-04
Abstract: 1,039,526. Radio-position finding. STANDARD TELEPHONES & CABLES Ltd. July 3, 1964 [July 4, 1963], No. 26457/63. Heading H4D. In a system wherein the position of a transmitting source 5, Fig. 1, is determined by combining the directions of the source from a plurality of spaced direction-finding stations 2, 3, and 4, the directions are each displayed on aligned indicators 22, 23, 24, Fig. 2, by the direction of a radial line or pointer, each indicator or its image is simultaneously scanned to produce a light pulse when the line or pointer is scanned, which light pulse is detected by a photo-electric device 25, 26, 27, and the time period between the instant of time coincidence between light pulses from the scanning of at least two of the indicators, which instant defines the point of intersection of the lines or pointers if they were superimposed and a reference signal occurring at a fixed time during the scanning of the indicators is determined. In a preferred embodiment the scanning is in a television raster form using a flying spot scanner 15, and two timer periods are determined, one using a reference signal synchronized with the line scan, and the other using a reference signal synchronized with the frame scan, to provide orthogonal (X and Y) position co-ordinates of the source. The scanner 15 simultaneously scans the indicators by means of semi-transparent mirrors 16, 17 and 18. Three directionfinding stations will provide three position fixes (i.e. the "cock hat") each having slightly different orthogonal co-ordice. In a preferred embodiment, the average is found of the X- co-ordinates and of the Y co-ordinates. The output of photoelectric devices 25, 26 and 27 are fed on lines 28, 29 and 30 respectively to the central station 1, where they are fed in pairs to AND gates 32, 33 and 34, Fig. 3. If pulses simultaneously appear on lines 28 and 29 for example, gate 32 produces an output pulse which is fed to timing circuits 35 and 38. Circuit 35 is also fed with a reference pulse on line 42 synchronized with the frame scan, whilst circuit 38 is fed with a reference pulse on line 43 synchronized with the line scan. Timing circuit 35 thus produces a signal, representing the time period between the instant of simultaneous appearance of pulses on lines 28 and 29 and the occurrence of the reference pulse. The signal thus also represents the Y co-ordinate of the source, using the direction-finders 2 and 3, and is fed to a Y-averaging circuit 44. Timing circuit 38 similarly produces a signal representing the X co-ordinate of the source, using the direction-finders 2 and 3, which signal is fed to a second or X-averaging circuit 45. Circuits 36 and 39 determine the Y and X co-ordinates of the source using direction-finders 3 and 4, whilst circuits 37 and 40 determine the Y and X coordinates of the source using direction-finders 2 and 4. The three Y signals are averaged to produce an accurate Y co-ordinate signal at 47 whilst the three X signals are averaged to produce an accurate X co-ordinate 45. One of the timing circuits 50 and one of the averaging circuits 44 is shown in detail in Fig. 4. The frame sweep waveform A, Fig. 5, is fed on line 55 to a charging capacitor 51, via an electronic switch 54, a switchable amplifier and a diode 52. The voltage across the capacitor starts to rise linearly as shown at 75 in waveform E. A pulse 78, waveform B, from one of the AND gates 35, 36, 37 is fed to trigger a bi-stable circuit 61 such that its outpput rises as shown at 81, waveform C. This causes switch 54 to change over, applying a cut-off negative bias 82, waveform D, to amplifier 53. The voltage 83, waveform E, across capacitors 51 thus stops rising. A bi-stable circuit 62 is fed with reference pulses 90, 80, 89, waveform G, synchronized with the flyback portions of the frame sweep waveform A, causing its output to vary as shown in waveform H. The circuit 62 also produces pulses 91, waveform J, synchronized with alternate reference pulses. Waveform C and waveform H are fed to AND gate 63 so that for the duration of portion 86 of waveform H the AND gate 63 produces a signal closing switch 59, and applying the voltage 83 waveform E across capacitor 51 to the averaging circuit. Since the rise of voltage across the capacitor is linear, voltage 83 represents the time period between coincidence pulse 78, waveform B and reference pulse 90 waveform G. Capacitor 51 is discharged by pulse 91, waveform J causing switch 58 to close, and the cycle is recommenced with circuit 61 returned to its initial state by pulse 91, waveform J and circuit 62 also returned to its initial state by pulse 89, waveform G. The average circuit 44 comprises an input resistor 69, 70, 71 for each timing circuit and a smoothing circuit 68. In a first alternative arrangement each indicator may be viewed by a separate television camera, the cameras having synchronized scans, and feeding their video outputs to coincidence gates. In a second alternative arrangement, separate but synchronized flying spot scanners may be used for each indicator. In a third alternative arrangement the pulses from the coincidence gates may be fed to the video input of a television monitor having the display time-base synchronized with the scanning of the indicators. Bearing line intersections will appear as dots, and the bearing lines may be also displayed faintly, by feeding the outputs of the photo-electric devices to the input of the monitor. The invention may be applied to optical and sound location methods.