Patent GB-1224044-A (GB)
Title: Automatic tuning radio receivers
IPC: H03J7/26
Filed: 1968-07-12
Abstract: 1,224,044. Automatic tuning arrangements. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 12 July, 1968 [24 July, 1967; 28 July, 1967 7 Nov., 1967], No. 33468/68. Heading H3Q. A radio receiver with automatic tuning employs electronic variable reactance tuning means and is characterized in that the automatic tuning control signal applied to the variable reactance means has superimposed upon it a bias corresponding to a frequency band it is desired to receive. In a first embodiment of the invention, if switch S1 is reversed, any one of a number of stations may be preselected by adjustment of the corresponding variable resistor VR1- VR5, the current through which, in conjunction with the current through the fixed resistor R5, constitutes the biasing current for currentcontrolled receiver tuning means B. With switch S1 returned to the position shown the receiver automatically tunes to the station selected by switch S2, the current which was derived from resistor R5 now being provided by an amplifier Tr2, Tr3 the input voltage of which is determined by the charge on a capacitor C1. This is charged over resistors R1, R3 and discharged at the end of a tuning sweep by means of a bi-stable circuit comprising Schmitt trigger pair Tr4, Tr5 coupled to emitterfollower Tr6 which discharges the capacitor, the base voltage of transistor Tr4 being derived from the emitter of transistor Tr2. When the selected station is tuned in, sweep is interrupted by means of a transistor Tr1 which becomes conductive when its base is biased from a detector following a narrow-band I.F. circuit in the receiver (Fig. 1, not shown). In a modification, the current-controlled receiver tuning means B, Fig. 6, receives current from two transistors Tr10, Tr11: the current through transistor Tr11 is set according to the desired station, by means of switch S and potentiometers RA, RA<SP>1</SP>- RE, RE<SP>1</SP>. The current through transistor Tr10 is determined by the charge on capacitor C1, which is charged through resistors R1, R3 and discharged by transistor Tr9 coupled to Schmitt trigger pair Tr7, Tr8. Charging is stopped upon tuning to the selected station, by means of transistor Tr1 which becomes conductive when its base is biased from a detector following a narrow-band I.F. circuit in the receiver (Fig. 5, not shown). Compensation for the temperature characteristics of the current-controlled receiver means may be provided in each of the stationsetting potentiometers RA, RA<SP>1</SP>-RE, RE<SP>1</SP>. Alternatively, it may be arranged that at the termination of a sweep, when the Schmitt trigger pair Tr7, Tr8 reverse, a negative pulse is applied over differentiating circuit C20, R20 and diode D20 to the base of transistor Tr11, momentarily suppressing the current through transistor Tr11. Circuit for holding sweep current constant, during reception of a station for which signal fading occurs.-The receiver tuning means 59 derives an operating voltage from the charge on capacitor 60, which is discharged at the end of a sweep by sweep returning circuit 61. To initiate a sweep, switch 68 is momentarily closed, discharging capacitor 67 and biasing transistor 65 conductive: capacitor 60 then charges via the emitter-collector path of transitor 65 and resistor 54. When the desired station is tuned in, a transistor 53 is biased conductive from a detector following a narrow band I.F. circuit in the receiver, and stops the further charging of capacitor 60. At the same time, an A.G.C. voltage applied to transistor 56 causes this transistor to become non-conductive whereby a transistor 63 becomes conductive. A path is thereby maintained between the collector of transistor 53 and capacitor 60, even though transistor 65 becomes non-conductive on the re-opening of switch 68. If the signal fades, transistor 56 becomes conductive, biasing transistor 63 non-conductive and so isolating the capacitor 60 to prevent its charge changing