Patent GB-761524-A (GB)
Title: Improvements in or relating to automatic gain control systems for radio navigation receivers
IPC: G01S1/24
Filed: 1954-12-23
Abstract: 761,524. Radio navigation; automatic gain control. SPERRY CORPORATION. Dec. 23, 1955 [Jan. 13. 1954], No. 37152/54. Classes 40(5) and 40(7) In a Loran receiver for measuring the time interval between two trains of pulses of equal repetition rate transmitted respectively from spaced A and B stations by matching the A and B pulses displayed on a cathode-ray tube, variations in amplitude of the smaller of the A and B pulse trains are substantially suppressed by applying positions A and B video pulses (inverted form of Fig. 3U) to a gating circuit 350 ("gain synchronizer") together with coincident 5Ás gating pulses 145, 146, Fig. 3T. the sampled A and B pulse outputs, Fig. 3X, being applied sequentially to storage capacitors 352, 353 respectively by a relay 130, 131 which is energized from a relay drive 132 by a square wave, Fig. 3D, derived from the timing circuit 25 so that the resultant positive D.C. voltages, Fig. 3Y and Z, across capacitors 352, 353 are proportional to the amplitudes of the A and B pulses. These D.C. voltages are applied through inverting valves 360, 361 to the anodes of diodes 362, 363 respectively, the cathodes of the diodes being connected together and through resistors 367, 368 to a negative voltage source so that only the diode to whose anode is applied the most positive D.C. voltage (corresponding to the smaller of the A and B pulses) is conductive and the gain control voltage applied to the mixer 16 and I.F. amplifiers 18 of receiver 12 from the junction of resistors 367, 368 is accordingly proportional to said most positive voltage. The gating circuit 350 preferably comprises a four - diode switch. Amplitude balance control. When the amplitudes of the A and B pulses are different there appears a relay contact 130 a square wave voltage BB. Fig. 3 whose phase and amplitude depend upon the relative amplitudes of the D.C. voltages Y and Z and this voltage BB is applied through cathode follower 354 and amplifier 355 to receiver 12 to balance the amplitudes of the A and B pulses. General operation. The invention is described as applied to a receiver of the type disclosed in U.S.A. Specification 2,651,033 in which the repetition rate of the A pedestal pulse and the variable timing of the B pedestal pulse are manually controlled as disclosed in Specification 644,579 to align the A and B pulses which are displayed on separate traces on a cathode-ray tube having the usual selectable slow, medium and fast timebase sweeps, Fig. 2 (not shown). The timing of the A pedestal pulse is then automatically controlled to maintain the A pulse located at a predetermined point on the A pedestal as disclosed in Specification 668,777 by applying differentiated A and B pulses V, Fig. 3 to a gate circuit in the A..F.C. circuit 116 together with 5Ás gating pulses 145, 146, Fig. 3T produced by differentiating 100Ás pulses S Fig. 3 initiated by the leading edge of negative A and B pedestal pulses applied to A.F.C. circuit 116 over lead 105 from the pedestal pulse generator 99. The sampled differentiated A pulses are applied to a long-time constant filter 124 by a relay 121, 122 operated like relay 130, 131 by relay drive 132 so that the amplitude of the D.C. error voltage W, Fig. 3, developed in filter 124 is proportional to any misalignment b#- tween gating pulse 145 and the crossover portion of the differentiated A pulse Fig. 4V and this error voltage W is applied to reactance tube 48 which controls the frequency of the 100 Kc/s master oscillator in timing unit 25 so as to reduce the misalignment. The gating pulses 145, 146 Fig. 3T for the amplitude control gate circuit 350 are produced by differentiating 100Ás S pulses applied thereto from A.F.C. circuit 116 are lead 127. The invention is also applicable to an automatic tracking Loran receiver of the type described in U.S.A. Specification 2,697,219.