GB471738A - Improvements in and relating to wireless and like receivers - Google Patents

Abstract

471,738. Wireless receiving-apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Feb. 4, 1936, No. 3383. Convention date, Feb. 4, 1935. [Class 40 (v)] A superheterodyne receiver using a relatively high intermediate frequency is provided with control means operating automatically to reduce tuning error actuated by a discriminating circuit fed with oscillations derived from intermediate frequency oscillations but of lower frequency. Fig. 1 shows a receiver in which the intermediate frequency is applied to a frequency changer 19 in the output of which is an error detector comprising tuned circuits 23<1>, 24<1> and differentially arranged rectifiers 22, 22<1>. Tuning is controlled by a voltage-operated electronic condenser and may be of the kind described in Specification 428,772. A switch 29 may be provided to render the frequency control inoperative to facilitate the tuning-in of weak stations and may be conjointly operated with the tuning control. In a modification, Fig. 2 (not shown), the tuned error detector circuits are included in the anode circuit of the frequency changer and the control is effected by varying the inductance of the local oscillator tuned circuit. For this purpose an inductance coupled to the tuned circuit is included in the cathode lead of a triode valve, the bias voltage of which is controlled. A variable impedance may be connected in series with a fixed reactance across the tuned circuit, Figs. 6 and 9 (not shown), or instead of the anode impedance of the valve being varied the mutual conductance or the grid conductance may be varied, Figs 7 and 8 (not shown). Fig. 10 shows a frequency changer T1 and an error detector comprising transformers with the primaries P1, P2 in parallel and damped by a resistance R1, the coupling to the secondaries S1, S2 which are tuned above and below the operating frequency being loose. The output of the differential rectifier T2 is applied to a triode T3 in shunt to an inductance 80 loosely coupled to the tuned circuit 81 of the local oscillator. Excess inductive admittance of the coil 80 is tuned out by condenser 82 and variation of the impedance of the valve varies the inductance 81. The condensers of the circuits 80, 81 are uni-controlled to keep the impedance reflected across the circuit 81 a combination of resistance and reactance of equal magnitude. The error detector rectifiers may be fed through separate amplifying valves, Fig. 5 (not shown). Specification 401,728 also is referred to. The Specification as open to inspection under Sect. 91 comprises also arrangements in which the intermediate frequency is not reduced in value before application to the error detector and in which the last amplifier feeds both the signal and error detector circuits in series, Fig. 6 (Cancelled, not shown). This subjectmatter does not appear in the Specification as accepted.