Patent GB-592509-A (GB)
Title: Improvements in radio apparatus
IPC: H04B1/38
Filed: 1944-02-10
Abstract: 592,509. Wireless apparatus. THOMSON, A. Feb. 10, 1944, No. 550/45. Convention date, Dec. 8, 1942. Divided out of 592,491, [Group XXXV]. [Class 40 (v)] [Also in Group XXII] A radio unit comprises an air-tight housing enclosing at least one tunable circuit, a flexible diaphragm sealed to one wall of the housing and having secured to it a thrust member within the housing, and actuating means, located outside the housing, for transmitting motion directly through the diaphragm to the thrust member, which operates tuning means within the enclosure. The invention embodies the tuning-coil apparatus of Specification 592,491, [Group XXXV]. The inductance is incorporated in a superheterodyne receiver circuit, Fig. 1, comprising an antenna 1 connected by a 36-ohm coaxial transmission line 2 to one end and a tapping 13 of an antenna coil 10 tuned by a powdered-iron core 12 and a ferromagnetic slug 15, the whole being shunted by a fixed condenser 11. The coil output is fed over condenser 20 to the grid of an R.F. amplifier VT1, the grid being fed over resistors and R.F. chokes 21, 22 from an A.V.C. or bias source A, and a filter capacitor 23. The plate of VT1 is connected over a similar tuning circuit 24 to the grid of a mixer VT2, shielded at 33 from VT1, and the circuit 24 has injected into it a voltage from an ultra-audion resonant oscillator circuit 62, the tuning coil 35 of which is coaxial with and similar to the coil 28 of circuit 24. The output of VT2 is connected to resonant circuit 40, transformercoupled to transmission line 42 and the receiverproper, the frequency being 5.2 M.C. The oscillator tuning circuit is connected across the grid and plate of valve VT3, the grid connection including a condenser 47 and resistances 49, 50 proportioned to give a negative biasvoltage at "A" for the grids of VT1 and VT2. The tap 53 is energized through a resistor 57 and choke 58 from source B and isolated by condenser 59. All cores 12, 12a are adjusted by a common dial 16 and adjustable connections 18 are included for lining-up. By suitable modification, the oscillator and antenna circuits can be adapted for transmission, Fig. 2 (not shown). The receiver head, Figs. 3, 8, comprises a two-part casing 80, 82 having bayonet-slot coupling between them so arranged that the two parts can only be assembled in one way, and a rubber gasket 125 ensures a weatherproof joint. A silica gel drying box is also provided. The terminalboard 128 is also sealed in weatherproof fashion thereto. The parts are all carried on a block 90, integral with casing-part 80 and having an upwardly-facing semi-cylindrical face, Figs. 8, 44, in which the various tuning-units are inserted and clamped by plates 96, 97 arranged so as to form rabbets with the block-walls. A shield plate 93, 95, forming the shield 33 of Fig. 1, separates the antenna tuning coil from the other apparatus and a further plate 94 separates the valves VT1, VT2, and supports the latter. The knob and dial 250, 255 for vernier adjustment is fixed to a lead screw 252, which thrusts on rod 115, Fig. 3, through the intermediary of a coarse-adjustment cam 259 having twenty-four steps, each corresponding to one M.C. A knob 262 operates the cam 259 through gearing and also moves a dial 271 located behind dial 255, the cam being capable of sliding axially as well as rotating, so as to interpose a progressively increasing thickness between the lead screw and rod. For this purpose the cam has twenty-five hardened steel balls 280 spaced round its rear and engageable in a depression in the end of rod 115. Each ball is hydraulic-pressed into a sphericalbottomed opening to a given depth so that its high point is at a given distance from the front face of the cam, and about 10 mils behind its neighbour on one side. In the front face, grooves 281 are cut corresponding to the ballsites, and hardened steel plates 279 fastened therein by C-shaped wire springs 283. The backs of the plates and the floors 282 of the grooves are correspondingly sloped, as shown, so that by means of tool 287, Fig. 3, each plate can be adjusted forwards into correct position, using standard frequency signals. A spring plate 276 with a series of fingers 277 retains the plates from the front. Specifications 560,779, [Group XXXVI], 592,510 and 592,513 also are referred to.