Patent GB-1307003-A (GB)
Title: Electric motor control circuit
IPC: H03J1/20
Filed: 1970-05-28
Abstract: 1307003 Control of AC motors RCA CORPORATION 28 May 1970 [2 June 1969] 25762/70 Heading H2J  An antenna 10 for intercepting television signals in the ultra high frequency band is coupled to a tuner 12 including a preselector and a local oscillator for generating heterodyning signals. A mixer circuit provides a modulated signal of intermediate frequency, the preselector and oscillator having variable tuning elements driven by a motor 20. A second antenna for intercepting very high frequency signals is coupled to a tuner for selecting one of a number of channels, and which may be switched to amplify IF signals from the tuner 12. The VHF tuner is connected through an IF amplifier to a video detector associated with a video amplifier and a picture tube. An intercarrier sound detector is connected through amplifying and demodulating stages to a loud-speaker. The composite video signal is amplified and applied to a sync. separator 36 providing vertical and horizontal synchronizing pulses. Automatic fine tuning circuits 42 are coupled between the IF amplifier and UHF tuner to keep the IF signal at the desired frequency. An automatic gain control circuit 44 develops a voltage which varies as a function of the level of the received television signal, this voltage being applied to the IF amplifier and the VHF tuner. The motor 20 may be controlled by a local switch or from a remote circuit 52, a signal sensing circuit stopping the motor when there is a desired television signal, this circuit being responsive to horizontal sync. pulses from the unit 36, and voltages from the circuits 44 and 42.  The motor is energized when one of the switches 64, 66, is closed and the transistors 82, 84, are conductive. When one of the control buttons 128, 130, is depressed the VHF tuner is switched to amplify IF signals from the UHF tuner and a control signal is provided through terminal 87 to close the transistor-switch 84. In addition one of the switches 64, 66 is closed depending on which of the buttons 128, 130 is actuated. A multivibrator 208, 211, closes the transistor-switch 82 for a period sufficient for the motor to drive the tuner away from a previously selected channel. The circuits 42 are prevented from affecting the UHF tuner. The multivibrator 208, 211 opens the transistor-switch 82 when a UHF signal of predetermined strength is received. The horizontal sync. pulses are integrated to provide a control voltage which is applied to one input of gate 314-316. As the UHF tuner scans the UHF frequency band, the control voltage produced by circuit 42 changes abruptly when a transmitted signal causes an IF signal which is within the pull-in range of the circuit 42. If horizontal synchronizing information and AGC voltage of sufficient magnitude are present, the gate circuit causes the multivibrator 208-211 to change state and open transistor-switch 82 and stop the motor. When the motor is deenergized, the circuit 42 produces an IF signal of the desired frequency.  To close the switch 64 and energize motor winding 60, transistors 70, 72 are rendered conductive with their emitters to earth through transistors 82, 84. The motor is reversed if the switch 66 is actuated. When the tuning shaft reaches a limit position, a time delay circuit becomes effective to reverse the drive. (For Figure see next page.)