Patent GB-632784-A (GB)
Title: Improvements in or relating to radio beacon receivers
IPC: G01S1/02
Filed: 1946-03-15
Abstract: 632,784. Radio navigation. STANDARD TELEPHONES & CABLES, Ltd. March 15, 1946, No. 8184. Convention date, March 26, 1945. [Class 40 (vii)] Relates to radio receivers for use in a rotating-beam beacon system of the type in which the beam is modulated by a composite wave having three distinguishable components, of which the first is of constant amplitude, while the amplitudes of the second and third vary as (1+sin #) and (1+cos #) respectively, where # is the instantaneous angular position of the beam. According to the invention the receiver comprises means for demodulating the received beacon signal, separately selecting the three components and separately detecting and integrating each selected component to yield unidirectional first, second and third signal voltages together with means for separately subtracting the first voltage from the second and third voltages and applying the two resulting differential outputs to the windings of a ratiometer to produce a field the direction of which is a function of the bearing of the receiver relative to the beacon. At the beacon, Fig. 1 (not shown), two signals A sin 2#F1t and A sin 2#F3t are modulated in phase quadrature at the frequency of rotation of the beam to give two resultant signals A(1+ sin #) sin 2#F1t and A(1+ cos #) sin 2#F3t, which are modulated on to the carrier together with a further constant amplitude signal A sin 2#F2t. At the receiver, Fig. 3 and Fig. 2 (not shown), the signals of frequencies F1, F2 and F3 obtained by demodulation are separated by filters and applied through amplifiers 15, 16 and 17 to detectors 25, 26 and 27, which produce voltages of amplitude A( 1+ sin #), A, and A(1+ cos #) respectively, across the storage condensers 31, 32 and 33, which are connected between earth and the cathode circuits of the detectors. The voltages A (1+ sin #) and A are applied to the grids of the triodes 34 and 35 so that a differential voltage A sin # is produced across the field coil 44 of the ratiometer 23 which is connected between the anodes of valves 34 and 35 and a differential voltage A cos # is similarly produced across the other field coil 45 by means of valves 36 and 37. The two field coils are mutually perpendicular so that the resultant field acting on the moving coil or magnet 47 is proportional to tan # and the pointer 46 then indicates the required bearing. If the bearing indicator was responsive to the instantaneous signals, the indication would vary as the beam swept past the receiver due to the finite width of the rotating beam and in order to prevent this, the storage condensers 31-33 are provided to give integrated signals, the amplitudes of which are proportional to the amplitudes of the signals received when the axis of the beam is directed towards the receiver. The signal from amplifier 16 is also applied through amplifiers 48 and 49 to operate a relay 50 which applies H.T. to the valves 25-27, thereby rendering them operative, and disconnects the cathode circuits of valves 34-37 from earth to render them inoperative when beam signals are being received, so that the ratiometer is only actuated by the integrated signals in the intervals between receipt of the beam signals; operation of relay 50 also causes a transient operation'of relay 52, which discharges the storage condensers so that the integration is independent of the signals previously received.