GB425659A - Modulation circuit for use in superheterodyne radio receivers and for like purposes - Google Patents

Abstract

425,659. Valve circuits for wireless reception. HAZELTINE CORPORATION, 15, Exchange Place, Jersey City, New Jersey, U.S.A.-(Assignees of Harnett, D. E. ; 16, Puritan Avenue, Tuckahoe, New York, U.S.A.) June 8, 1934, No. 17002. Convention date, Aug. 12, 1933. [Classes 40 (iii) and 40 (v)] The circuits of the frequency-changing stage of a superheterodyne receiver are so arranged that the same variable condenser serves for tuning the receiver to the incoming signal and for tuning the local oscillator. As shown in Fig. 2 applied to a superheterodyne receiver, the input from the aerial coil L1 is applied to a tuned circuit comprising a coil L2 and a tuning- condenser C2 connected across the grid and cathode of a pentode mixing-valve 15. The local oscillation is generated by a back-coupled valve 17, the tuned grid circuit of which comprises the tuning-condenser C2, a small condenser C3, a large blocking condenser C4 shunted by a resistance R4, and a coil L3. The frequency of the local oscillator is considerably higher than that of the incoming wave, so that the impedance of the network for the high local frequency is not materially affected by the coil L2, while the impedance for the lower incoming frequency is not materially affected by the branch C3, L3, C4. The difference frequency, which is fed from the plate of the valve 15 to the amplifier 20, is higher than usual. Any local oscillation fed to the aerial 11 by the coil L2 is balanced by a circuit connected from the plate reaction coil L4 through a condenser C1 to the aerial. The local oscillator employs magnetic reaction L4, L3 combined with capacity reaction due to the condenser C4 situated in both grid and plate circuits. An amplifier may be interposed between the aerial and the coil L2, Fig. 3, (not shown), or a multiple-grid valve may combine the functions of the valves 15, 17, Fig. 4, (not shown).