Patent GB-503717-A (GB)
Title: Improvements in or relating to navigation aiding radio transmitting installations
IPC: G01S1/02
Filed: 1938-07-25
Abstract: 503,717. Directive wireless signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. July 25, 1938, No. 22108. Convention date, July 28, 1937. [Class 40 (v)] Relates to a radio beam transmitter in which crossed Adcock aerials are combined with a central non-directional aerial to radiate a rotating field of cardioid shape with one or more fixed-reference signals. This allows a distant receiver fitted with a cathode-ray or similar type of indicator to secure a direct reading of its bearing. According to the invention, the operation of the transmitter is supervised by a monitoring-device comprising a cathode-ray tube which indicates when the aerial currents are correctly phased. As shown in Fig. 1, low-frequency current from the main supply 1 is fed to the anodes of a pair of balanced modulators 15, 17 which energize one pair of spaced aerials E, W, and through a second pair of modulators 19, 21 to the other pair of aerials N, S. Carrierfrequency current is supplied to the modulators from a source 27 which also feeds the centre aerial C. Keying is effected by sharply interrupting the carrier wave, at Geographical North, or other fixed-reference points, by current derived from a rectifier 73, which is supplied from the A.C. source 1. The keying-current passes through filter circuits to gas-filled tubes 81, 83, one or four fixed-reference signals per cycle being given, according to whether one or both of the tubes 81, 83 are brought into circuit by the switch 85. Radio-frequency currents supplied by the modulators 15, 17 to the aerials E.W. are in phase-opposition, and so are those supplied by the modulators 19, 21 to the aerials N.S., whilst that supplied to the centre aerial C is in quadrature. The resulting field is a cardioid which rotates about the centre aerial C at the frequency of the main supply 1, and which ceases during the keying intervals, i.e. when the maximum of the cardioid points to one or more fixed points of the compass. The balance of the modulators is corrected by differential condensers 41, 43 and 57, 59 whilst the modulating-currents for the N, S, E, W aerials are kept in correct phase by adjusting the tapping point 7 and inductance 9 until the dynamometer 108 shows zero torque. The transmitting system is monitored by inductively coupling each aerial to the deflecting plates of a cathode-ray indicator, Fig. 2 (not shown) which shows by characteristic traces when the correct phase-relations have been established. In the superhet receiver, Fig. 4, the incoming signals are subjected to AVC and, after amplification and rectification at 113, 115 and 117, are applied through a phase-splitting circuit 141 to the deflecting plates 143, 145 of a cathode ray indicator 147'. The fixed reference signals are fed to the, control grid 151 from a transformer 153. The rectified currents at the output of the receiver are of the form shown in Figs. 5A ... 5D, and on the screen of the cathode ray indicator produce circular traces Z, as shown in Figs. 6A ... 6D respectively, the gaps in the trace, (which indicate the bearing of the receiver), are calibrated by taking test readings on a uniform field rotated either from the aerial C alone, or in combination with one or other of the pairs of spaced aerials. The cathode-ray indicator may be replaced by a dynamometer driven by the rotating field component. The position of the needle gives the bearing when viewed stroboscopically by the light from the Neon lamp, which is triggered by the fixed reference signal. Or a synchroscope indicator of known type may be used.