Patent GB-913363-A (GB)
Title: Radio navigation receiver
IPC: G01S1/02
Filed: 1959-06-19
Abstract: 913,363. Radio navigation; automatic phase-control systems. STANDARD TELEPHONES & CABLES Ltd. (International Telephone & Telegraph Corporation). June 19, 1959, No. 21114/59. Classes 40 (5) and 40 (7). Relates to a mobile receiver for indicating the bearing of the receiver from a TACAN radio beacon transmitting a rotating multilobe pattern, Fig. 2 (not shown), together with coded groups of main and auxiliary reference pulses from which are derived at the receiver 15 c/s. and 135 c/s. coarse and fine bearing-dependent sinusoidal signals and 15 c/s. and 135 c/s. main and auxiliary sinusoidal reference signals, the required bearing being given by the phase difference between the bearing-dependent and reference signals. The 15 c/s. bearing and reference signals are applied to a coarse phase discriminator controlling a servomotor 59 coupled to a bearing indicator 60 and to a phase shifter 42 operating on the input 15 c/s. bearing signal to bring the inputs to the coarse phase discriminator into a predetermined phase relationship, e.g. phase quadrature, and the 135 c/s. bearing and reference signals are applied to a fine phase discriminator which, when the output from the coarse phase discriminator falls below a predetermined value, is coupled to the servomotor 59 which is also coupled through a 1 : 9 gearing 101 to a phase shifter 81 operating on the 135 c/s. reference signal to bring the inputs to the fine phase discriminator into a predetermined phase relationship so that the bearing indicator 60 is first set roughly by the coarse control system and then accurately controlled by the fine control system. In such a system the coarse phase discriminator produces a false null output when the phase-shifted input 15 c/s. bearing signal is phase displaced by 180 degrees from the condition corresponding to the predetermined phase relationship and according to the present invention means are provided for discriminating between the true and false null conditions and, when a false null condition occurs, for preventing control of the servomotor by the fine discriminator and for applying to the servomotor a " shift " voltage from a source 75 which rapidly rotates it away from the false null condition. Coarse control.-As shown, the 15 c/s. bearing signal from a filter 25 is applied to the phase shifter 42 whose output is applied to a phase inverter 43 giving two out-of-phase components, Fig. 4, A and B, which are combined respectively at points 41 and 42 with the 15 c/s. reference signal, Fig. 4, C, from a filter 34 to give two resultant signals, Fig. 4, D and E, which are applied to peak rectifiers 45, 49, 50 and 48, 51, 52, whose differential D.C. error voltage output is converted into a corresponding phase sensitive A.C. error voltage in a control circuit 58 and applied to the control winding 76 of the two-phase servomotor 59. Fig. 4, A-E, shows the phase conditions for a true null, and Fig. 4, F-J, shows the corresponding phase conditions for a false null. The differential D.C. error voltage output from the peak rectifiers 45, 49, 50 and 48, 51, 52 is also applied to a modulator 92 to produce an A.C. signal of amplitude inversely proportional to the error signal which is converted into a corresponding D.C. control voltage in a detector 93 and applied to a D.C. bias source 72 (see below). The 15 c/s. bearing signal output, Fig. 5, A (same as Fig. 4, A), from the phase inverter 43 is also applied to a 90-degree phase shifter 64 whose output, Fig. 5, B, is combined at 65 with the 15 c/s. reference signal Fig. 5, C (same as Fig. 4, C) to give a resultant, Fig. 5, D, whose peak amplitude exceeds a predetermined threshold value only when a true null condition obtains as shown in Fig. 5, A-D; Fig. 5, E-H shows the corresponding phase conditions for a false null. Any signal in excess of the threshold value is selected by an amplitude discriminator 67 and rectified at 68 to give a true null-indication voltage which is applied (1) to block a diode 74 thereby preventing application of the shift voltage 75 to the motor winding 76, (2) to an indicator 80 to indicate the occurrence of a true null and (3) to the D.C. bias source 72 (see below). If the phase shifter 42 assumes a position corresponding to a false null, there is no output from the amplitude discriminator 67 and accordingly the shift voltage 15 is applied to the motor winding 76 and the indicator 80 gives a false null warning indication. Fine control.-The 135 c/s. reference signal from a filter 35 is applied to the phase shifter 81 whose output is applied to a phase inverter 82 giving two out-of-phase components which are combined respectively at points 84 and 86 with the 135 c/s. bearing signal from the filter 26 to give two resultant signals which are applied to peak rectifiers 79, 95, 97 and 78, 96, 98. The C.R. components of the 135 c/s. rectifiers are in series with the corresponding C.R. components of the 15 c/s. rectifiers and the diodes 79 and 78 of the 135 c/s. rectifiers are normally blocked by the D.C. voltage from the bias source 72 which is suppressed only when the true null-indication voltage is supplied thereto from the detector 68 and when a null indicator voltage is applied thereto from the detector 93. Specification 778,448 is referred to.