Patent GB-1308010-A (GB)
Title: Signal seeking tuning systems
IPC: H03J7/30
Filed: 1970-05-28
Abstract: 1308010 Automatic tuning arrangements RCA CORPORATION 28 May 1970 [2 June 1969] 25761/70 Heading H3Q  In a signal seeking tuning system for a T.V. receiver having mechanical driving means 20 coupled to drive tuning means 12 to scan through a frequency range, control circuitry is responsive to the presence of synchronizing pulses 36, a predetermined level of automatic gain control voltage 44 and a control output voltage from an automatic fine tuning (AFT) control circuitry 42 indicating that the receiver is tuned to a frequency within the pull in capability of the AFT circuitry to de-energize the driving means 20 and stop the tuning means 12 before the tuning means is accurately tuned to a selected television channel whereby the inertia of the driving means causes further change in the tuning means in the direction for accurate tuning for the selected channel. Starting tuning motor.-In the T.V. receiver shown grounding terminal 120 or 122 by remote control or closing manual control button 128 turns on transistors 156, 162 and diodes 164, 166, 168 and triggers monostable circuit 188, 190 so that transistor 190 is turned off for a predetermined period. A control voltage at 170 switches the V.H.F. tuner to provide an I.F. amplifier for the U.H.F. tuner 12 and a control via 87 enables transistor 84 to conduct after a delay provided by capacitor 90 and resistor 92. The output from monostable circuit 188, 190 turns on transistor 204 which lowers the voltage at 206 so as to change the state of a bi-stable circuit 208, 211 to make transistor 208 off and 211 on and enables transistor 82 to conduct. The state of a bi-stable circuit 176, 178 is changed by the control voltage from diode 168 to make transistors 176 off and 178 on. The output from bi-stable circuit 176, 178 turns on transistor 180 which provides a positive bias via line 68 to turn on transistors 70, 72 and energize winding 60 of the A.C. motor 20 to drive the tuning of the preselector (14, Fig. 1, not shown), and oscillator (16) of the U.H.F. tuner 12 in one direction. Also during rotation of the motor 20 transistor 272 is operated to prevent the automatic fine tuning, AFT, circuit 42 from operating and to mute the video and audio signals. Rotation of the tuning motor in the opposite direction is obtained by remote control or manual operation of button 130 to provide a control voltage at 124 or 126. This turns on transistors 234 and 240 and diodes 242, 244, 246 which operates the monostable circuit 188, 190 and bi-stable circuit 208, 211 in a similar manner to before, to enable conduction of transistors 82 and 84. The control voltage from diode 246 changes the state of bi-stable circuit 176, 178 to its other state and via transistor 254 turns on transistors 106, 108 to energize the winding 58 of the motor 20. A switch or switches is actuated when the tuning shaft of the U.H.F. tuner 12 rotates to its end positions so as to control via lines 290 or 292, delay circuits 306, 308 or 298, 300, diodes 310, 312 or 302, 304 the monostable and bi-stable circuits 188, 190, 208, 211 and change the state of bi-stable circuit 176, 178. This changes the switching transistor pair 70, 72 or 106, 108 to reverse the drive direction of the tuning motor 20. Stopping tuning motor.-The tuning is stopped when the point 206 goes positive due to AND gate 314, 316 receiving horizontal synchronizing signals from sync. separator 36, on AGC signal from 44 and a single from AFT circuit 42. After monostable circuit 341 has been triggered a number of times by sync. pulses from 36 the integrating capacitor 358 will have discharged to a level such that transistor 364 is turned on. The output at 366 is then periodically connected to ground via 364, 356 when the monostable circuit 341 is triggered by the sync. pulses. When there is no incoming U.H.F. signal diodes 384, 386 are reverse biased. When a signal is detected provided it falls within the AFT pullin range it forward biases one of the diodes 384, 386 to cut off transistor 376 and gate transistor 314 continues to be biased on. Also provided the AGC voltage is sufficient to turn on transistor 392 the gate transistor 316 is turned on. Then the transistor 314 is periodically made non-conductive due to the periodic switching on of the transistors 364, 356 under control of the sync. pulses. A positive potential is periodically developed at the collector of transistor 314 when transistor 316 is conductive 316 is conductive so that the first positive pulse changes the state of the bi-stable circuit 208, 211 to turn off transistor 82 and stop the motor. The signal level at which the AGC voltage enables gate 14, 16 is controllable by potentiometer 410 so that the viewer can adjust the receiver to tune in only strong signals. The oscillator (16) of the U.H.F. tuner has its resonant frequency above that of the preselector (14) so that the preselector attenuates image signals and by adjusting the potentiometer 410 the signal seeking circuitry is prevented from stopping on the image signal. The AFT circuit 42 is connected between the IF amplifier (22) and the U.H.F. tuner to develop a correction voltage from the variation of the IF and applies this correction voltage to a variable capacitance to adjust the oscillator frequency. The AFT circuit may be as in United States Specification 3,444,477. The remote control may use a transmitter (54) and receiver (52).