Patent GB-631668-A (GB)
Title: Improvements in or relating to radio navigation systems
IPC: G01S1/30
Filed: 1946-08-12
Abstract: 631,668. Radio navigation; valve circuits. GRENFELL, A. R., and DECCA RECORD CO., Ltd. Aug. 12, 1946, No. 23900. [Classes 40 (vi) and 40 (vii)] A receiver for a radio navigational aid of the type in which spaced transmitters radiate alternately two sets of synchronized signals to create two differing patterns of equi.phase difference contour lines such as the third embodiment described in Specification 630,867 with reference to Figs. 5 and 6 thereof, comprises first and second phase difference measuring devices brought into action alternately in step with the switching of the transmission and means for indicating the difference between the phase difference measurements. Specification 630,867 discloses a system of determining the particular lane in which the receiver is situated in an equi-phase difference field pattern navigation system and in the particular embodiment referred to this information is obtained by determining the difference between the phase difference values measured in the normal equiphase difference pattern from which accurate contour line information determining a location line is derived, as in Specification 620,479, on an alternately created pattern having a different number of lanes. Fig. 2 indicates how in the transmission periods of normal transmission 9 are followed after a short interval t<1> by periods of the alternate transmission 10 between which and the next period 9 there is a longer interval t<2>, and Fig. 3 (not shown) details the arrangements required at three spaced transmitters used to create intersecting patterns for position determination.. In the system described, the three stations A, B and C radiate at frequencies 60 kc., 80 kc. and 90 kc. in their normal mode of operation and 59¥ kc., 79<2>/3 kc. and 89# kc. in the alternative mode. Transmitters B and C are of slave type and radiate signals having a fixed multiple phase relation with those of the main transmitter A. At the receiver signals from a common aerial 26 are fed to receivers 27, 28, 29, and 30, which pass signals from the C, A, A, and B, stations respectively, their pass-bands being wide enough to accept both the normal and alternate transmissions. Receiver 27 feeds converter 31, doubling the frequency of the applied signals and receiver 28 feeds converters 32 and 33 respectively, trebling and quadrupling the frequency of its output while the output of receiver 30 is trebled in frequency in converter 34. The output of each converter is fed to two switching valves, rendered conductive alternately by switching pulses synchronized with the transmitter switching over lines 43 and 45, so that during normal operation the phase difference between the outputs of converters 31 and 32 is shown by phase indicator 52 and that between the outputs of converters 33 and 34 by indicator 54. During the alternate mode of transmission the corresponding phase indicators are 51 and 53. The indications of indicator 52 are displayed by needle 56 (Fig. 5) carried by hollow shaft 55 which extends to differential 57 also fed, as shown, by the indicator 51 and the difference value of the indications of units 51 and 52 is displayed by needle 60 carried by shaft 59. In such a display, needle 56 gives the accurate phase difference contour on which the craft is situated with lane ambiguity and needle 60 shows the lane. A similar display system combining indicators 53 and 54 provides the information necessary for a positional fix. The synchronization between the transmission changeover and the switching of the converter outputs is accomplished by receiver 29 feeding rectifier 46. The rectified output is inverted and short pulses of length t<1> interspaced with longer pulses of length t<2> applied to synchronizer 44 which applies negative bias to line 45 following the short pulse and on the arrival of the long pulse transfers the bias to line 43 and so on. Valve circuits. A suitable synchronizer circuit (Fig. 6) operates with two gas-filled valves 64 and 67 whose plate circuits are coupled by a commutating capacity 79. The cathodes are connected respectively to outputs 43 and 45 and through resistors 71 and 72 to a point of negative potential on the supply battery.. The input 61 is fed through capacitor 62 and resistor 63 to the grid of valve 64 and also through capacitor 65 and resistor 66 to the grid of valve 67. The grids are also coupled by capacitors 74 and 75 to the respective cathodes and through resistors 76 and 77 to a source of negative bias. The time constant of the combination 66-75 is made sufficiently long to prevent valve 67 conducting on application of the short pulses t<1> while it will conduct on application of the longer pulses t<2>. The time constant of the combination 63-74 is short enough for the valve 64 to conduct for either length of pulse. In operation a pulse t<1> causes valve 64 to conduct, the current therethrough and through resistor 71 raising line 43 to approximately earth potential; line 45 still having the full negative potential on it. This state continues till the subsequent application of a pulse t<2> causing valve 67 to conduct and switch off valve 64 owing to the capacitor 79. Line 45 is then at earth potential and line 43 negative. The following pulse t<1> again causes valve 64 to conduct and switches off 67 and so on. Specifications 620,480 and 620,507, [both in Group XXXVI], also are referred to.