Patent GB-1379759-A (GB)
Title: Electrical tuning system
IPC: H03J7/08
Filed: 1971-12-06
Abstract: 1379759 Channel tuning arrangements; AFC arrangements MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 6 Dec 1971 [7 Dec 1970 (3)] 56635/71 Headings H3Q and H3A In a tuning system having a channel selector with a tuning element 17 which determines the tuning frequency of the system, an automatic fine tuning (AFT) circuit 15, the output of which is direct current connected without interposition of any active circuit element to the input of the tuning element 17, first switch means 3 is operable to provide a D.C. potential to power the channel selector at least when the tuning system is being tuned to a selected one of a predetermined number of channels and a suppressor circuit including a semi-conductor switch means 7, 14 is operable by the D.C. potential to prevent the output of the AFT circuit 15 being applied to the tuning element 17 until the system is tuned to the selected channel. In the tuning system shown for a colour T.V. receiver on switching on a supply switch 22 the automatic suppressor circuit operates so that transistor 14 conducts to apply a voltage Eo to the varactor diode tuner 17 and so suppress the output from the AFT circuit 15. The I.F. picture carrier is applied to the input 16 of the AFT circuit 15. After a time determined by resistors 11, 29 and capacitor 20 transistor 7 conducts and transistor 14 turns off so as to allow the AFT voltage from 15 to be applied to the tuner. When it is required to change the channel, switch 3 is operated to either position so as to drive the motor 4 forward or reverse. This drives a channel selecting circuit 17 which supplies in a changing over operation tuning voltages corresponding to predetermined channels for the varactor-tuner 17. Also the automatic suppressor circuit operates so that transistor 14 conducts to suppress the AFT output during the tuning operation. A manual AFT suppression circuit may be operated to position 24 so as to also cause the automatic suppressor circuit to operate. In modifications (Figs. 17 and 18, not shown) the manual AFT suppression switch 21 may be connected between the transistors 7 and 14 or between the transistor 14 and the AFT circuit 15. A modification providing forward and reverse operation of the motor but excluding transistor 7 is disclosed (Fig. 14, not shown). In a simplified embodiment (Fig. 9, not shown) single direction of rotation of the motor is provided and the transistor 7 and its associated circuitry are omitted. In modifications (Figs. 11 and 12, not shown), the automatic suppressor circuit (TR1) operates to inhibit a voltage supply (E2) to the AFT circuit (A) so as to suppress its output. In a further modification (Fig. 13, not shown) the automatic suppressor circuit (TR1) operates to suppress the I.F. picture carrier at the input to the AFT circuit (A) so as to disable the AFT. In a further embodiment (Fig. 7, not shown), the D.C. potential is applied to the channel selector (SL) which may be manually or motor driven to provide a tuning voltage to a varactor tuner (V) and to a delay and hold circuit which makes a transistor (TR1) in the AFT suppressor circuit conduct to prevent the output from the AFT circuit (A) being applied to the varactor tuner (V) until the selected channel has been tuned. In a colour television using the tuning system (Fig. 1, not shown) the output of the I.F. amplifier feeds a detector whose output feeds a video circuit, chrominance circuit, audio circuit or synchronizing circuit. Specifications 1,130,139 and 849,394 are referred to.