Patent GB-625404-A (GB)
Title: Improvements in or relating to radio transmitters
IPC: H03J5/00
Filed: 1938-05-13
Abstract: 625,404. Radio transmitting apparatus. DODDS, J. M., LUDLOW, J. H., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. May 13, 1938, No. 14371. [Class 40 (v)] [Also in Group XXXVII] In a short-wave radio transmitter comprising a pair of push-pull valves 38, Fig. 9, and a plurality of different inductances 28, 29, 30 in fixed relation to the valves, a switch is provided having at least two movable arms 20 hinged to the valve electrodes to which the several inductances are to be selectively connected for varying the wavelength. The hinges, switch arms and the contacts of the inductances are of relatively large dimensions in the direction parallel with the axis of the inductance loop formed by those parts. Transmitter. The anodes of the valves 38 may be connected to any one of the inductances 28, 29, 30, by the switch arms 20 which are mounted on a common shaft 21, Fig. 7, hinged to the anode terminals 18. The inductances are fed with H.T. at tappings 43, which also may be selected by a switch arm, and each inductance is connected through blocking condensers 39 and feeders 40 to a separate dipole aerial 42. The grids 44 are connected to a screening box 45 and the control grids are connected to a tuning condenser 5a and through further switch arms, to grid inductances connected by concentric conductors to the preceding stage. All the inductance switches of the transmitter, including similar switches in preceding stages, may be operated simultaneously either manually or by motive power controlled by push-buttons. Switch constructions. The anode terminals 18, Fig. 7, of the two valves carry lugs 19 forming hinges for the switch arms 20 which are operated simultaneously by a shaft 21. The two switch arms co-operate with three pairs of jaws, one pair 23 of which only is shown, mounted on a panel and interconnected with corresponding inductance coils, e.g. 28. To obtain shorter wavelengths the coils 28 may be replaced by straight bars. Further shortening of the wavelength may be secured by mounting bridges 28a across the jaws 23. The bridges may be extended as at 28b between the switch blades. Instead of a bar, a hollow box-like member may be employed. Each switch arm 20 is broad in the direction parallel with the effective axis of the inductance loop formed by the two arms. In a modification, each switch arm 20 comprises a pair of blades resiliently held apart by a spring and cooperating with a jaw having inturned knifeedged contacts which engage the outer faces of the switch arm. Metal foil may be soldered to the switch blades to improve the H.F. characteristics of the switch arm. To ensure good contact, the knife-edged contacts of the switch jaws co-operate with different pairs of lines on the outer faces of the switch arms. The system of switching as described is applicable to both " parallel " circuit arrangements wherein the inductances, together with its parallel tuning or trimming condenser, is connected between the anodes of the two valves and " series " circuit arrangements wherein the condenser and inductance are in series and are connected between the control grids. Specifications 414,753, 458,702, 476,188, 497,359, 625,405, 625,406 and 625,408 are referred to.