GB312698A - Improvements in radio receiving apparatus - Google Patents

Abstract

312,698. Kramolin, L. L. de. May 31, 1928, [Convention date]. Thermionic heterodyne receivers. -In a superheterodyne receiver, the incoming and the local oscillations are applied to separate grids in a multi-grid valve. The receiver is designed to receive on two wave bands and the intermediate frequency is chosen to lie between the two bands. The aerial is connected by a switch 7 to either of two bandfilters arranged to respond to the two bands of waves to be received. The aerial oscillations are applied to one grid of the multi-grid valve 1. The local oscillations are generated in a tuned circuit 6 connected to one or more further grids in the valve 1, and back-coupled to the plate circuit. The oscillations serve substantially to paralyse the valve 1 during one half-cycle, and to allow it to operate as an amplifier during the other half-cycle. This manner of operation is stated to diminish interference by undesired frequencies. The circuit 6 has a tapping connected to the switch 7 so that the local frequency band is selected simultaneously with the incoming frequency band. Tuning is effected by a single control connected to the variable condenser of the circuit 6. The intermediate frequency amplifier comprises valves 2, 3, 4 with tuned inter-valve circuits, and stable working is ensured by using screen-grid valves in stages 2 and 4, and a frequency-doubling valve in stage 3. Push button or like selection of desired stations may be provided for by switching in selected condensers across the coil of the tuned circuit. A screw adjustment of the condensers may be provided for final accurate tuning. Specifications 301,498 and 311,295 are referred to. The Specification as open to inspection under Sect. 91 (3) (a) states that the local oscillations may be produced by one of the valves 2 - - 5, or that an independent valve may be used. This subject-matter does not appear in the Specification as accepted.