Patent GB-856152-A (GB)
Title: Searching and tracking receiver for radio navigation system using complex signals
IPC: G01S13/78
Filed: 1958-09-05
Abstract: 856,152. Radio navigation; automatic phase control systems; phase detection. STANDARD TELEPHONES & CABLES Ltd. Sept. 5, 1958 [Sept. 10, 1957], No. 28587/58. 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 135c/s. coarse and fine bearing-dependent sinusoidal signals and 15 c/s. and 135 c/s. main and auxiliary reference pulses, the required bearing being given by the phase difference between the bearing-dependent and reference signals. According to the present invention the 15 c/s. bearing signal is applied from a filter 25 through a phase shifter 35 to a monostable multivibrator 36 to give 15 c/s. 30 degrees gate pulses (i.e. ratio of pulse duration to 15 c/s. recurrence period = 30/360) which are applied to a coincidence detector 37 together with the 15 c/s. main reference pulses from a separator 28 and the phase shifter 35 is rotated by a motor 45 energized from a D.C. source 49 through a motor control circuit 40 and the contact arm 50 of a relay 39 which is initially in the upper "search" position as shown. When the inputs to the coincidence circuit 37 are coincident the resultant output from the circuit 37 energizes the relay 39 thereby changing over the relay contact arms 51 and 50 to the "tracking" position to (1) increase the duration of the gate pulses from the multivibrator 36 to 40 degrees and (2) disconnect the motor control circuit 40 from the D.C. source 49 and connect it to the output from a phase discriminator 44 to which are applied (1) the 135 c/s. auxiliary reference pulses from a separator 29 and (2) a 135 c/s. square wave produced by applying the 135 c/s. fine bearing signal from a filter 26 to a square wave generator 43 through a phase shifter 42 controlled by the motor 45 through a 1 : 9 step-up gearing 48. The motor 45 now adjusts the phase shifter 42 until the auxiliary reference pulses overlap equal positive and negative portions of the 135 c/s. square wave; when this condition obtains there is zero output from the discriminator 44, the motor 45 is de-energized and an indicator 46 driven by the motor 45 indicates the required bearing. If the 15 c/s. bearing signal fails, the relay 39 will return to the "search" condition and the reason for increasing the duration of the gate pulses from the multivibrator 36 during tracking is to prevent such a return due to momentary changes in the 15 c/s. bearing signal. The phase discriminator 44 comprises two diodes 58, 59 reversely connected to a storage capacitor, the 135 c/s. square wave being applied to the diodes in push-push and the 135 c/s. reference pulses being applied in push-pull by means of transformers 56, 57, so that a D.C. error signal is produced across the storage capacitor if the reference pulses deviate from a position in which they overlap equal positive and negative portions of the 135 c/s. square wave. The motor control circuit 40 may be as disclosed in Specification 837,914.