Patent GB-487687-A (GB)
Title: Improvements in or relating to tuning controls for radio receivers
IPC: H03J5/08
Filed: 1936-12-23
Abstract: 487,687. Adjusting wireless apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Dec. 23, 1936, No. 35294. Convention date, Dec. 23, 1935. [Class 37] [Also in Group XL] A tuning-control for a radio receiver comprises a rotatable station selector disc carrying a plurality of finger holds or apertures for effecting rotation of the disc to a predetermined fixed stop which comprises an element adapted to move or rock between a pair of stop members. The finger holds 41, Fig. 2, are adjustably secured to the periphery of the disc 44 by set-screws 43 and house spring-loaded buttons 42 carrying station identification labels on their front faces, each having a metal pin on its rear side. The disc 44 is connected to the tuning condenser spindle of the receiver through a 2 : 1 gearing to tune to any individual station, the operator inserts his finger in the appropriate device 41 by depressing the button 42. This causes the pin behind the button to project and the disc is then rotated in either direction until the projecting pin meets a fixed stop, as will be explained in connection with Fig. 1. The disc 44 also carries a circular wavelength scale 51 with a fixed pointer 92. An auxiliary knob 94 may be provided as a supplementary control. The invention also contemplates the employment of tuning controls of the above kind in conjunction with wireless receivers having automatic frequency control systems such as described in Specifications 471,738, [Group XL], and 489,094. Such a combination is schematically shown in Fig. 1, and has for its object to overcome the difficulty in A.F.C. systems that the receiver tends to remain tuned on a relatively strong undesired signal when tuning to a weaker signal. The arrangement employs a tuning disc 40 with fingeroperated controls 41, the fixed stop comprising a rocking lever 46 which closes a pair of switch contacts 47 when the pin 45 on the rear of the selected station button strikes the lever from either side. This switch effectively earths the A.F.C. control voltage line 26 by closing spring contacts 32, 33, and thus renders the A.F.C. inoperative just prior to the station being tuned in. The operator removes his finger from the depressed button, and the lever 46 returns to its mid-position ; the contacts 32, 33 re-open and the automatic frequency control system brings the receiver into exact tune. An auxiliary switch 30 is provided for cutting out the automatic frequency control when not required. The timing disc 40 operates the timing condenser spindle through a 2 : 1 gearing 46, 47 in order to give a 360 rotation of the disc for 180 displacement of the condensers. The disc 40 may be mounted directly on the timing condenser spindle in which case the devices 41 are all mounted on one half of the disc periphery, Figs. 6 and 9 (not shown); or two diametrically opposite switch-stops may be arranged to co-operate with the disc 40, and the devices 41 may then be arranged round the whole disc periphery, Fig. 11 (not shown). The switch stop may be arranged as a centre-pivot lever in front of the disc 40 and is then actuated by the operator's finger, Fig. 6 (not shown). Specifications 341,464 and 437,442 also are referred to.