Patent GB-1396039-A (GB)
Title: Automatic tuning control circuits
IPC: H03J7/12
Filed: 1972-05-11
Abstract: 1396039 Automatic control of position R C A CORPORATION 11 May 1972 [17 May 1971] 22033/72 Heading G3N [Also in Division H3] In apparatus for automatically controlling the tuning of a TV receiver having a tuning means 24, 25 which may be tuned to any one of a plurality of television channels dependent on the magnitude of an applied tuning control voltage which determines the reactance of a voltage variable device in the tuning means, the apparatus comprises a bi-directional motor 11, Fig. 1, motor control means 8, 9, 10 for driving the motor in one or other of its two directions, and first switching means 2 having a plurality of first contacts each one of which is associated with a different one of a plurality of potentiometers 6 providing a selectable tuning voltage. The first switching means has a first selector contact coupled to the motor 11 so as to be driven by the motor to access any one of the potentiometers and the associated tuning control voltage and means 1, 3 provide an inhibiting signal to the motor control means 8, 10 accompanying accessing of one of the potentiometers so as to stop the motor with the tuning means tuned according to the control voltage provided by that potentiometer. In Fig. 1 operation of up or down channel selection switches 21 or 22 causes delayed operation of a pulse start generator 16 such as a monostable circuit (123) Fig. 5, (not shown), Fig. 6a due to operation of a noise immunity monostable circuit 32 or a delay circuit 122. The output from the monostable generator 16, 123 operates a start/ stop bi-stable memory 8, 125 which provides a muting output 29 to disable the sound and vision of the TV, disables the AFC and enables a motor switch 10(129), 157 Fig. 6b. The operation of the up or down switch 21 or 22 determines the state of a bi-stable memory 9, 126 so as to select up or down driver (127 or 128) 178 or 184 for operation of the up or down motor switch (130 or 131) 161, 163 or 160, 162 so as to energize winding 165 or 165' and drive the motor in one or other direction. The motor 132 drives four 20 position mechanical rotary switches 1-4 formed as a printed circuit Fig. 7, (not shown). The rotary switches 1-4 select channel indicating lamps (100-102) Fig. 4 (not shown), pre-set potentiometers (45-47) Fig. 2 (not shown), for providing a selected tuning voltage to voltage variable reactance devices such as varactor diodes in the VHF and UHF tuners 24, 25, low and high VHF band and UHF band switching voltages to switching diodes in the VHF and UHF tuners and preadjusted voltages for a meter scale selector 18 (43) (222-228) Fig. 8, (not shown), providing an indication of the channel selected. When the moving contact (107) Fig. 4, (not shown), contacts the next fixed contact (104) a positive voltage is applied via a diode 14, 153 to reset the start/stop memory 8, 125 and stop the motor. The motor may be arranged to skip any channel position by adjusting the channel selection potentiometer (47) to one end of its range which operates a switch (105') to short out its associated lamp. The AFC voltage is obtained from a discriminator 70, Fig. 3 fed from the video IF carrier and is amplified by transistors 71, 72 and is used to modulate a reference voltage obtained from a series regulator 79 connected to the tuning voltage potentiometers (45-47). The regulator 79 may be an integrated circuit. The positive AFC disabling signal obtained from a diode 156 Fig. 6a during channel selection when the motor is energized causes transistor 82 to saturate and clamp the output from the transistors 71, 72 to a constant value determined by a Zener diode 83. The AFC is also disabled when the tuning potentiometers (45-47) are being adjusted since when a door 30 is opened for access to the tuning potentiometers a switch 28 is closed as shown in Fig. 1 to apply a positive voltage to the transistor 82 so as to clamp the output of the AFC transistors 71, 72. Further the AFC is disabled for a few seconds after switch on of the receiver since the transistor 82 is again tuned on until a transistor 86 conducts after a delay caused by the charging time constant 89, 90. The receiver may be controlled remotely by an ultrasonic controller 20.