GB536917A - Improvements in or relating to modulated-carrier signal receivers of the homodyne type - Google Patents

Abstract

536,917. Valve circuits for wireless reception. HAZELTINE CORPORATION. Feb. 12, 1940, No. 2693. Convention date, March 4, 1939. [Class 40 (v)] [Also in Group XXXV] In a homodyne receiver having means responsive to the frequency of the signal carrier wave for maintaining the local oscillations in synchronism with the signal carrier, additional means responsive to the phase difference between the two oscillations are provided for maintaining the phase difference within predetermined limits. The aerial 10 is coupled by a selector circuit tuned by a condenser 13 to a radio-frequency amplifier 12 the output of which is coupled by a transformer 14, 15 to the input circuit of two square-law detectors 16, 17 connected in a balanced circuit. A local oscillator 18 has its frequency determined by an inductance 19 tuned by a condenser 31 coupled to the input grid of 18, and a feed-back inductance 191 coupled to inductance 19, condenser 31 being ganged with condenser 13. With the above arrangement, the amplified signals are applied in parallel and the local oscillations in push-pull to the detectors 16, 17 whence the output is passed through a low-pass filter to the output stages. Synchronization of the oscillator 18 with the signal carrier is ensured by a coil 30 coupled to coil 14 and connected to a negatively biased grid of valve 18. The phase control circuit comprises a pair of diodes 41, 42 to which the incoming signal is applied in the same polarity through inductances 43, 44 and to which an output voltage of oscillator 18 is applied with opposite polarity by means of a coupling circuit 45, 46. Equal load resistances 48, 49 are provided, and the resultant differential direct current voltage is applied through a filter 51 - 55 to bias the input circuit of a valve 56 which is connected so as to simulate a. shunt inductance across circuit 19, 31 variable in magnitude in accordance with the bias applied from detectors 41, 42. The bias varies with the phase difference between the signal carrier and the local oscillator and so the arrangement serves to maintain this difference constant. An A.V.C. potential may be taken from the negative end of load resistance 49. There is also coupled to primary winding 14 a winding 32 across which are connected in series in resistance 33 and condenser 34, which elements together with primary 14 and condenser 35 comprise a two-terminal dead-end filter serving as a broad-band selector.