Patent GB-769509-A (GB)
Title: Hyperbolic radio navigation receivers
IPC: G01S1/24
Filed: 1954-12-08
Abstract: 769,509. Radio navigation; discharge tube relay circuits. SPERRY CORPORATION. Dec. 8, 1954 [Feb. 1, 1954], No. 35579/54. Classes 40(6) and 40(7) The invention is described as applied to a Loran receiver of the type described in U.S.A. Specification 2,697,219 for measuring the time interval between two trains of pulses of equal repetition rate transmitted rerespectively from spaced A and B stations in which first and second locally generated pulse trains A<SP>1</SP> and B<SP>1</SP> are automatically maintained coincident with the received A and B pulses respectively, the B<SP>1</SP> pulses being derived from the oscillator from which the A<SP>1</SP> pulses are derived by means of a calibrated delay device. The received signals are also applied to a grating circuit 128 controlled sequentially by the A<SP>1</SP> and B<SP>1</SP> pulses, the sampled A and B pulse outputs being applied respectively to storage capacitors 352, 353 by a cyclically-operating relay 130, 131 to give D.C. voltages of amplitude proportional to the received A and B pulses respectively which are utiliized for balancing and stabilizing the amplitudes of the received A and B pulses as described in Specification 761,524. According to the present invention the D.C. voltages also control a relay 406 controlling a lamp 407 such that the lamp is lit when both control voltages are present but is extinguished when either or both control voltages are absent due to failure of either or both of the A and B signals. The relay may also control a contact S16 in the energization circuit of a motor 94 controlling the B<SP>1</SP> delay means. When both the A and B transmitters are operating but not in the required time relationship, such faulty operation is indicated by periodically shifting the relative timing of the transmitted A and B pulses by a discrete amount, e.g. 1000 Ás. at one second intervals and such a "blinking" type of transmission causes lamp 406 to blink in synchronism. The invention is also applicable to systems such as disclosed in Specification 761,524 and U.S.A. Specification 2,651,033 in which the timing of the B<SP>1</SP> pulses is controlled manually. Circuit details. The D.C. voltages from capacitors 352, 353 are applied 'through inverting valves 360 361 to the anodes of diodes 362, 363 and the cathodes 365, 366 of the diodes are connected together and through resistors 367, 368 to a negative voltage source so that the resultant negative potential at cathodes 365, 366 is proportional to the amplitude of the smaller of the received A and B pulses. A negative gain control voltage from the junction of resistors 367, 368 and an amplitude balance control voltage (A, A, B, C) from contact 130 of relay 131 are applied to receiver 12 as described in Specification 761,524. The coil of relay 406 is connected between the anodes of a double triode 391 and the cathodes 365, 366 of diodes 362, 363 are coupled to the grid of the right-hand section of valve 391 such that under normal conditions this section is cut-off. A negative voltage proportional to the mean noise level at the input to detector 19 of receiver 12 is applied from the detector output through low-pass filter 400, 403 to the grid of the left-hand section of valve 391 which is positively biased by potentiometer 401 such that under normal conditions this section is conductive and hence relay 406 is energized. If either or both of the A<SP>1</SP> and B<SP>1</SP> pulses are no longer coincident with the received A and B pulses, e.g. due to transmitter failure, the potential at the diode cathodes 365, 366 becomes more positive and the right-hand section of valve 391 becomes conductive; the gain of receiver 12 is also increased and the increased noise voltage cuts off the left-hand side of valve 391 but the resistance of the anode load 405 of this section is so great that the resultant current through the coil of relay 406 is insufficient to maintain the contacts 515 and 516 closed and hence lamp 407 is extinguished and the energization circuit of motor 94 is broken. If the R.F. section of receiver 12 is inoperative, the A and B pulses are absent but there is no increase in the noise voltage and under such conditions both sections of valve 391 are conductive and relay 406 is again de-energized. Finally if both A and B pulses are present and the noise voltage increases due to a fault in the A.G.C. circuit both sections of valve 391 are cut off and relay 406 is de-energized. The anodes of diodes 362, 363 are also coupled through capacitors 412, 413 to the grid of a triode 392 whose anode is coupled through capacitor 415 to the grid of the left-hand section of valve 391 so that under "blinking" fault conditions an A.C. signal (of period one second) is applied in push-pull to the two sections of valve 391 and lamp 407 blinks accordingly. General operation. The alignment of the A<SP>1</SP> and Bl pulses with the received A and B pulses is first effected manually by conventional pulses matching on a cathode-ray tube having selectable slow, medium and fast timebase sweeps as described in more detail in Specification 761,524 and U.S.A. Specifications 2,697,219 and 2,651,033; the A<SP>1</SP> pulses are synchronized automatically with the received A pulses as described in Specification 668,777 and U.S.A. Specification 2,697,219 and the timing of the B<SP>1</SP> pulses is controlled as described in Specification 644,579 and U.S.A. Specification 2,697,219.