Patent GB-496129-A (GB)
Title: Improvements in or relating to direction finding radio receiving systems
IPC: G01S1/02
Filed: 1937-05-22
Abstract: 496,129. Directive wireless signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 22, 1937, No. 14327. Convention date, Jan. 11. [Class 40 (v)] Relates to direction-finding receivers having a cathode ray tube for providing a visible indication of the direction of incoming signals and comprises means whereby the bearings of two or more transmitters can be simultaneously indicated and " night effect " is eliminated. The signals from the crossed loop aerials 1, 2, Fig. 1, after conversion to an intermediate frequency by valves V1 ... V4 are combined by the coupled coils 32, 33 to produce signals in the output circuit 78, 79 of a following I.F. amplifier 95 the phase of which is dependent on the direction of the incoming signal as described in Specification 488,611. The second channel interference rejection circuits associated with the frequency changers are described in Specification 496,154. Signals from an open aerial A are changed to the same I.F. by valves V5, V6 and appear in the output circuit 43, 44, 45 of amplifier 42 from which components in phase quadrature are applied through valves V7, V8 to balanced modulators 69, 70 and 71, 72 where they are modulated respectively by two currents in phase quadrature from a low frequency generator comprising valves V9, V10. The modulated signals from the circuits 66 .... 68 and 61 .... 63 are combined by coupled coils 64, 65 and applied through valve V11 to a coil 80 coupled to the output circuit 78, 79 of the directional system. A valve V12 rectifies and amplifies the combined output of the circuit 78, 79 and applies the resultant potentials developed across the cathode resistance 86 to the control electrode 89 of the C.R. tube V 13. The beam in the tube is rotated by potentials in phase quadrature derived from the valves V9, V10 and applied through transformers 52, 53 and 55, 56 to the mutually perpendicular pairs of deflecting electrodes. Once per revolution, the signals from the openaerial are in phase opposition to those from the crossed loops and the cathode ray is cut off, the point where the spot on the screen disappears being arranged to correspond to the direction of the incoming signal. Alternatively the luminous indication on the screen may be arranged to be present only at the point of beam rotation corresponding to the required direction. In order to eliminate " night effect," the switch 98 is closed to connect the circuit 78, 79 to an amplifier and delay circuit 87 operating a relay 90 so arranged that the cathode beam is cut off by the bias source 88 a few milliseconds after the arrival of a signal. Alternatively an A.V.C device with a predetermined delay and quick control operation may be used. In order to give a position indication the directions of two transmitters may simultaneously be indicated by rapidly switching the tuning circuit 20 ... 24 of the local oscillator V1 from one frequency to another corresponding to the correct settings for the two transmitters in question, by motordriven switches 25, 26. In front of the screen of the C.R. tube is provided a transparent map 3, Fig. 2, mounted for movement in any direction and rotatable guides 5, 5<1> fixed at the positions on the map corresponding to the two transmitters carry rods 4 pivoted at an axis O over the centre of the C.R. tube screen. The map is moved until the rods pass through the gaps 1, 2 in the fluorescent track 6 when the point O indicates the position of the receiver.