Patent GB-633076-A (GB)
Title: Improvements in or relating to radio-position indicating systems
IPC: G01S1/02
Filed: 1946-10-17
Abstract: 633,076. Radio direction-finding. STANDARD TELEPHONES & CABLES, Ltd., EARP, C. W., and GODFREY, R. M. Oct. 17, 1946, No. 30919. [Class 40 (vii)] A position - indicating system comprises a plurality of radio direction-finding stations which deliver signals, each of which varies in accordance with the direction from the respective station to a transmitter to be located, these signals being applied in sequence to a cathode-ray tube in such a fashion that, corresponding to the signals received from each direction-finder, a trace is produced on the screen of the cathode-ray tube, the trace originating from a point representative of the position of the corresponding direction-finder and extending in a direction corresponding to that from the direction-finder to the transmitter, so that the traces intersect to give a " fix " indicating the position of the transmitter. In the embodiment described, each direction-finder delivers four unidirectional voltages which bear such a ratio to one another that by suitably applying them to the deflecting-plates of a cathode-ray tube, the electronbeam is deflected in a direction corresponding directly with the direction of reception. The voltages from the direction-finders DFI, DF2, DF3 are applied to the common anode connections of the pairs D1, D2 of diodes. A positive biassing-potential is superimposed on each direction-finder output so that the diodes D1 are normally conductive and condensers C are normally discharged. Pulse outputs from the pulse generator PG render the diodes D1 corresponding to each direction-finder successively non-conductive. When any one set of diodes becomes non-conductive, the corresponding condensers C charge and thus in the absence of any other deflecting signals cause a radial trace to be drawn on the screen of the cathoderay tube CRO, the direction of the trace corresponding to the direction -of reception of the then operative direction-finder. Means are provided for displacing the origin of the trace to a position corresponding to that of the direction-finder. The pulse generator PG which may be of the type disclosed in Specification 596,699 delivers a six-phase output and the first pulse of the cycle, which is from output 11 and does not cut off diodes D1, is applied to cathode-followers VA, VB via potentiometers P1 and P2 which are so adjusted that the currents in the coils LA<1>, LB<1> deflect the cathode-ray beam to the desired position where a bright spot is produced representing the direction-finder DF1. The second pulse of the cycle from output 12 deflects the beam similarly, butalso renders the diodes D1 non- conductive so that a direction-indicating trace is produced. Similar bright spots and traces corresponding to direction-finders DF2 and DF3 are produced in response to later pulses of the cycle. The pulse-generator may be arranged to supply more than six phases, the additional phases being used to produce additional luminous spots on the screen indicating the locations of desired reference points. A map or reference grid is applied to the screen of the cathode-ray tube, e.g. by etching on the screen or by optical projection. Details of direction-finders. The system employed at each direction-finding station is based on that disclosed in Specification 490,940 and comprises four dipoles located at the corners of a square, opposite pairs of dipoles being cross-connected, and a fifth centrallyplaced dipole. The output from one pair of dipoles is modulated with a 5 kc/s. modulating signal in a balanced modulator which suppresses the carrier. The output from the other pair of dipoles is similarly modulated with a 6 kc/s. signal. The modulated signals, comprising side-bands only, are fed, together with the signal from the central dipole, to an amplifier and detector system at the output of which are obtained signals having frequencies of 5 kc/s. and 6 kc/s. and also any speech modulation which may have been present in the received signal. The 5 kc/s. and 6 kc/s. signals are selected by filters and each fed to a separate differential detector of the type described in Specification 579,117, to which is also fed the corresponding 5 kc/s. or 6 kc/s. modulating signal. The differential detectors consequently deliver outputs corresponding in amplitude and sign with the amplitude and phase of the signals delivered by the corresponding dipole pairs. The outputs of the two differential detectors are then taken to the four terminals, shown in the Figure as the output of each directionfinder, on which are also superimposed the biassing potentials previously referred to. Specification 426,328 also is referred to.