Patent GB-721805-A (GB)
Title: Improvements in signal seeking radio receivers
IPC: H03J5/00
Filed: 1953-01-09
Abstract: 721,805. Radio receiving sets; adjusting radio apparatus. GENERAL MOTORS CORPORATION. Jan. 9, 1953 [Jan. 29, 1952], No. 678/53. Class 40 (5). The invention relates to radio receivers of the type in which the tuning scans its wave-range and is automatically stopped by a received signal when it is tuned in, and in which preset tuning is effected by de-sensitizing the receiver except in small selectable bands including the desired signal frequencies. According to the invention the bands are selected by switches each of which connects into circuit a contact adjustably movable along the path of movement of a contact on the tuning indicator needle and which when in contact with the needle contact restores the sensitivity of the receiver. The tuning cores of the permeability tuned circuits of the receiver shown are mounted so as to be movable in one direction by a spring acting through a planetary carriage 64 and linkwork under the control of an air governor 72 driven through a gear train 68, 70. The carriage has ears 74 which at the extremes of movement of the carriage operate a limit switch 76 which causes a solenoid 78 to rapidly return the carriage to one end of its range and recharge the spring. On operation of the central one 8 of push-buttons 4, 6, 8, 10, 12, a bar 138 (Figs. 2 and 5), moves to the left momentarily operating a switch 148 (Fig. 2), which initiates the tuning. The movement of the bar also latches the button and releases the previously depressed button. When a signal is tuned in a circuit, described below, causes a relay 86 to move a latch 90 into the path of the air governor 72 to arrest the tuning. To enable selection of a particular station four indicators 168 are provided. These comprise a pointer portion 190 visible in front of the tuning dial and are slidable along a bar to position the pointers at the desired tuning points. The indicators also comprise a U- shaped contact 172 (Fig. 5), one end of which is in sliding contact with a respective one of conductive rails 174, 176, 178, 180 and the other 186 of which lies on an insulating block 184. A tuning pointer 104 is provided which is driven by the tuning carriage and is arranged by suitable linkages to move in a straight line path across the tuning dial. The tuning pointer carries a contact which slides along the insulating block 184 and connects in turn to the contacts 186. These may be connected in circuit by means of the respective push- ,buttons since they comprise a conductive plate 134 carried by and insulated from the button base plate 112 and which when the button is operated bridge a corresponding pair of contacts 192, 1921. The tuning arresting circuit is only operative when the pointer contact is in connection with the operative one of contacts 186 and the tuning is therefore only effective in a narrow band including the desired frequency. The electrical circuit is shown in Fig. 6. When the aforesaid button 8 is operated a resistance 308 is inserted in the cathode circuit of the receiver H.F. and I.F. valves to reduce the sensitivity in accordance with the selected setting of the resistance. In addition, operation of the button momentarily operates a switch 152 (as described above). Contact 150<SP>1</SP> of this switch mutes the receiver and contact 150, as it is connected to an earthed line 298 causes a relay 86 to operate and to start the tuner, as described above. Contact 2361 removes an earth from the cathode line 312. The relay is held operated by the current through the right hand half of a valve 212. When a signal of sufficient strength is tuned in a large enough positive voltage is applied through line 218 to the grid of the left-hand half of valve 212 to render it conducting. This cuts off the current through the right. hand half and so releases relay 86 causing the tuning to stop (as described above) and earthing the cathode line to restore full sensitivity. Operation of one of the push buttons 2, 4, 6, 10 and 12 initiates tuning as before but leaves the cathode circuit of the valves broken. This however is restored when the earthed moving contact 188 connects with the operative indicator 20, 22, 24 or 26 permitting tuning to be arrested as before. The front panel of the set is provided with a knob 32 which may be pulled outwards to operate the mechanism for raising and lowering the aerial.