Patent GB-1395919-A (GB)
Title: Device for automatic tuning of television receivers
IPC: H03J7/24
Filed: 1972-05-23
Abstract: 1395919 Touch responsive switches AUTOVOX SpA 23 May 1972 24089/72 Heading G1N [Also in Division H3] In a device for automatic tuning of a TV receiver having a variable capacity diode tuner, the device has a sawtooth generator 1, Fig. 2, producing a sawtooth biasing signal g for the variable capacity diode and for a band switching circuit (2), Fig. 1 (not shown) and Fig. 3, when a video carrier signal l applied to an amplifier, limiter and discriminator circuit 4 is present a control signal is produced which is applied to operate a blocking circuit 5 so as to stop sweep operation of the sawtooth generator 1 and an electronic switch 11  is operated to allow the supply of the control signal to the blocking circuit 5 on receipt of a rectified sound intercarrier signal c so as to stop the sweep operation of the sawtooth generator 1. On switching on, transistors Q001, Q002, Fig. 3, switch on and a band feed voltage for the tuner is applied from I. The capacitor C179, Fig. 2 of the sawtooth generator 1 is charged via Q154 and the 0.3 secs sweep is ended by Q156, Q157. The change in output at g operates Q013 to turn Q003, Q004 on and turn Q001, Q002 off so as to provide a different band switching voltage at 111 and to connect different timing resistors to the sawtooth generator 1 at e, f to alter the next sweep time to 0.6 secs. Similarly at the end of this sweep Q005, Q006 turn on to connect the UHF band switching voltage and provide a further sweep time of 2 secs. At the end of this time the first stage Q001, Q002 is turned on again and the above is repeated. The transistor Q153 of the signal search circuit is maintained blocked by the negative potential at i when no television signal is received. If an I.F. sound intercarrier signal occurs at c it operates via intercarrier amplifier 6 and intercarrier detector 8 on electronic switching unit 11 so that transistor Q152 conducts to remove the negative potential at i. If an I.F. video carrier signal now occurs at I the amplifier, limiter Q151 and discriminator 4 provide an output to turn on Q153 and stop the charge of the capacitor C179 so as to hold the receiver tuned to the received signal. To restart signal seeking a touch sensitive switch (12), Fig. 1 (not shown) is touched so as to operate transistors Q045, Q046, Fig. 4 to provide a signal at b. This block Q153 so as to commence sweeping of the generator 1. Also the signal at b makes Q161 conduct to discharge C178. Transistor Q161 conducts to make i negative until C178 has charged after 3 sec when Q160 turns off. This automatic time switch 7 acts to keep the receiver tuned to a detected station even if the sound carrier of the detected station fades. Also a memory circuit 13 acts to prevent loss of the channel to which the receiver is tuned to due to temporary loss of the video carrier since loss of the video carrier causes Q163 to conduct and Q164 to block so as to prevent charging of the sweep capacitor C179. A local distant switch (14), Fig. 1, (not shown) may be switched so as to connect the output from a current generator 10 to the AGC system of the receiver so as to obtain a decrease of gain of the RF stage when a signal sweep is made. A channel indicator (3) may be connected to the band switching circuit (2), Fig. 3, and to the tuning voltage from the sweep generator 1.