Patent GB-626471-A (GB)
Abstract: 626,471. Radio navigation. SADIR-CARPENTIER. July 4, 1946, No. 20079. Convention date, Oct. 12, 1944. [Class 40 (vii)] In a system for the radio-navigation of a movable craft comprising a receiver on the craft co-operating with a fixed equi-signal overlapping beam beacon, the receiver comprises a loop aerial periodically switched in phase and co-operating with an omnidirectional aerial to provide switched cardioid reception patterns, and means for deriving from the beacon signals received on these alternately operative reception patterns a voltage indicative of the divergence of the craft from the beacon course-line and a voltage indicative of the heading of the craft with respect to the direction to the beacon, these voltages being applied to an indicator to produce an indication directing the craft so as to bring it on to the beacon course-line. The invention is applicable to systems employing beacons using modulation either of the simultaneous or complementary type. In a receiver for a system employing complementary dotdash signals a voltage of frequency f<1> is applied to the thermionic switch 31 to periodically reverse the phase of the output of the loop aerial 12 which is combined in series with the output of aerial 11. The combined signal is applied to frequency-changer 15 and thence to intermediate-frequency amplifiers 16 and 17 and the diode 18, the output of which, Fig. 5, comprises a signal at the frequency f of the modulation of the beacon signal. This signal is amplified at 19 and applied to rectifiers 20 and 21. The output circuit of rectifier 20 which is tuned to the switching frequency f 1, delivers a signal of frequency f<1> varying at the dot-dash frequency which is amplified at 24 and applied to the thermionic switch 43, which is operated in synchronism with the switch 31. Current consequently flows in either winding 42 or 44 according as to whether the heading of the craft is to the left or the right of the direction to the beacon. The output circuit of diode 21 comprises a condenser behaving as a short-circuit to signals of frequency f<1> so that the output comprises a unidirectional signal varying in amplitude at the beacon dot-dash frequency. This signal is amplified at 22 and applied to winding 37. The resultant voltage induced in secondary winding 45 due to the current flowing in both primary windings is applied to the meter 38. The changes in flux occurring at the change from a dot to a dash signal or vice-versa, generate voltages which are applied to the meter which is so constructed that it is insensitive when deflected from its zero position, so that it responds only to the transition from a dash to a dot. A zero indication on the meter indicates that the craft is following a logarithmic spiral course which will eventually intersect the beacon axis. Fig. 8 (not shown) illustrates means for causing the course to approach the axis asymptotically. A further very long time-constant output circuit for rectifier 21 is provided, so that the circuit delivers a unidirectional voltage which varies according to the mean amplitude of the dot-dash signal. The transformer winding 41 is returned to the output point of the circuit, which thus provides a gain-control signal for the amplifier 24. It is so arranged that the gain is increased as the beacon axis is approached and the course defined is so modified as to cause the craft to approach the beacon axis asymptotically. In the receiver system illustrated in Fig. 9 (not shown) for use with a beacon. simultaneously modulated by frequencies f1, f2' the aerial system is switched at the frequency f<1> as before. Signals of frequency f1, f2, varying at the frequency f<1>, are filtered out from the output of the second detector and applied to separate rectifiers each of which delivers a unidirectional voltage corresponding to the mean amplitude of the input signal and a voltage of frequency f<1> corresponding to its variation in amplitude. The difference between the two signals of frequency f<1> is obtained, amplified, and then applied to a thermionic switch operated at the frequency f<1> to deliver an output whose sign is dependent upon the direction of the beacon relative to the heading of the craft. This signal is applied together with the two unidirectional outputs from the rectifiers to a multi-coil galvanometer. The mean of the unidirectional voltages which is arranged to decrease as the beacon axis is approached is applied to the amplifier of the signals of frequency f<1> to act as, a gain control as in the previous embodiment. In the embodiment illustrated in Fig. 10 (not shown), which is also applied to a simultaneous modulation system, the signal of frequency f<1> is derived by direct rectification of the received signal. This is applied to the meter together with a signal derived from the difference between the modulation signals of frequencies f1, f2. This provides a course which approaches the beacon axis asymptotically. To provide a more rapid approach control means are provided to reduce the amplification of the signal of frequency f<1> as the beacon axis is approached.