Patent GB-494026-A (GB)
Title: Improvements in or relating to the automatic tuning of superheterodyne radio receivers
IPC: H03J5/14
Filed: 1937-05-10
Abstract: 494,026. Electric control systems. GENERAL ELECTRIC CO., Ltd., PETERS, W. H., HUNTER, S. G., and CHUBB, A. A. May 10, 1937, Nos. 13287 and 14070. [Class 40 (i)] [Also in Groups XL and XXXV] A radio receiver is tuned to any one of a plurality of desired frequencies by means of push-buttons each of which controls an auxiliary maintaining circuit for a relay controlling the tuning motor the circuit being broken by a member coupled to the tuning device when the receiver is nearly in tune with the desired station, upon which further movement of the tuning member is arrested by reception of the desired signal. Fig. 1 shows a control system in which desired frequencies are selected by a number of pushbuttons 1 ... 6 each retained, when depressed, by locking plate 21 and released either by depression of another button or by a relay 22. Closure of each button completes two circuits by means of spring contacts 15 ... 20, the first circuit operating relay A or B through leads 8 ... 13, conducting stop-members 23 ... 28, wire 30 or 29 and metal pulley or rod 33 or 32. The wire 29, 30 is a travelling band wound round and operated by the spindle 34 which is coupled to the tuning condenser shaft of the receiver. The wire is divided into two conducting portions by insulators 35, 36 and a further insulating portion 31 which is arranged to break the circuit of relay A or B (made by closure of one of switches 15 ... 20) when it passes or contacts with a stop member 23 ... 28 corresponding to the button depressed. In the example shown, relay A is energized by depression of any one of buttons, 18, 19, 20 and relay B by any one of the other three ; in a practical embodiment of such a receiver there would be twelve buttons, six only being shown. Actuation of relay A closes contacts A1, A3 and opens contact A2. Closure of A1 energizes a synchronous motor 37 which rotates in a direction determined by a starter device 39 described in connection with Fig. 2. The motor 37 rotates the tuning element, and also the shaft 34, in such direction that the insulated portion 31 moves towards the stop member (e.g. 28) corresponding to the button depressed (e.g. 6). On reaching member 28, the portion 31 breaks the circuit 13, 30 of relay A thereby permitting subsequent de-energization of the relay on opening of the contact O1. As soon as the desired signal is exactly in tune an arresting device (not shown) operates a relay which opens contact O1; the relay A is then de-energized, contact A3 and A1 re-open, A2 closes and the motor 37 stops. The arresting device may comprise a sharply-timed crystal circuit coupled to the I.F. stage (in the case of a superheterodyne receiver) and feeding an anode-bend rectifier with a relay in its anode circuit ; when the receiver is exactly in tune the relay operates. The same sequence of operations takes place on relay B if, say, button 1 is depressed, but in this case the motor 37 would rotate in the opposite sense so that insulator 31 moves to the right until it breaks the relay circuit at member 23. The actuation of relay A or B governs the direction of rotation of motor 37, by a starter device shown in Fig. 2 in which 1 and 2 are the stator and rotor of the motor proper, the shaft 3 of which carries a disc 4 having a projection 5 and a spring-loaded stud 10 which bears against the inner side of a pivoted stop lever 6. This lever is swung about its pivot by members 11, 12 operated by relays A or B respectively and when so operated to either extremity, one or another of the projections 8 or 9 lies in the path of the cam 5. The motor may initially rotate in either direction, but in the position shown clockwise rotation is prevented. The motor then rotates anticlockwise and the frictional contact of the stud 10 then moves lever 6 to the mid-position so that both projections 8, 9 are clear of the cam 5. Waveband switching is effected by switch 54 which energizes relay C or D and starts up the motor 59 driving the switch-discs 57, 58. Closure of a push-button 1 ... 6 automatically causes actuation of the switches 58, 57 to give the required long or short-wave band irrespective of the position of switch 54. Tone and volume are controlled by push-buttons 42, 43; 48, 49 operating motors 46, 52 through relays E, F ; G, H. All the apparatus above the line XY may be located at a remote point, and the tone, volume and waveband controls 42<1>, 43<1>; 48<1>, 491 and 54<1> may be duplicated at the receiver. The local tuning is effected by the two-way switch 61<1>, 62<1>, 631 which directly operates motor 37 through relays A, B. The wire 29, 30 may be adjacent the receiver tuning scale and may carry an indicating pointer to act as the station indicator ; the shaft of motor 37 may also be extended to a knob serving as a slow-motion adjustment for the tuning element. The receiver is muted during tuning by contacts operated by relay A or B. Switching over from remote to local control is effected by switch 40, lamp 41 being lit when remote control is operative. Switches A2, B2 delay release of a depressed button until relay A or B falls on completion of the timing operation. Specification 433,298, [Group XL], is referred to in the first Provisional Specification.