GB789168A - Improvements in or relating to carrier demodulators - Google Patents

Abstract

789,168. Phase-sensitive circuits. DECCA RECORD CO., Ltd. Dec. 7, 1955 [Dec. 10, 1954], No. 35894/54. Class 38 (4). [Also in Group XL (c)] The amplitude and phase sense of a modulated carrier is detected by pulse sampling the carrier at short intervals of time corresponding to the same phase of the carrier frequency, then integrating the pulses in a Miller valve circuit with capacitive negative feedback and whose time constant during the sampling pulses is made small so that it rapidly follows any sudden change of amplitude or reversal of phase. As shown, the carrier is applied through a cathode follower valve 12 and second cathode follower 18 to a diode bridge gate 20-23 rendered conducting by positive or negative switching pulses synchronous with the carrier frequency so that the instantaneous amplitude of the carrier is applied to the grid of a Miller integrator valve 24, whose integrated output applied through a cathode follower 42 measures the amplitude and phase sense of the carrier. Alternating current negative feedback is also applied from the anode of the integrator valve 24 to the grid of the cathode follower 18 so that the difference of the two inputs to its grid is very small and the sampling pulses may be of small amplitude. Further, D.C. negative feedback is applied from the output 43 through a cathode follower 52 to the mixer cathode follower 18 to stabilize its D.C. level. Equal positive and negative H.T. voltages energize the valves to render the output symmetrical. The output D.C. level may be varied by varying the D.C. bias applied back to the valve 18 from a potentiometer 46 having a constant voltage drop across it derived from a gaseous circuit tube 45 in the derived from a gaseous tube 45 in the cathode circuit of the valve 42. The circuit may be used in # sweep radar P.P.I systems for detecting the amplitude and phase sense of the quadrature voltages respectively induced in the stator coils from the rotor. Specification 679,723, [Group XL (c)], is referred to.