Patent GB-1193783-A (GB)
Title: Improvements in Radio Frequency Channel Selector Devices
IPC: H03J5/02
Filed: 1968-01-24
Abstract: 1,193,783. Receiver tuning arrangements. COMPAGNIE FRANCAISE THOMSON HOUSTON-HOTCHKISS BRANDT. 24 Jan., 1968 [24 Jan., 1967], No. 3787/68. Heading H3Q. [Also in Division G4] In a channel selector for receivers, such as television, a member 12 translates data, which is characteristic of a particular channel and carried on a support 13 in coded form, into electrical signals which are fed to a digitalanalogue converter 11 and the output from the converter 11 is fed via one or more D.C. amplifiers 9, 10 to one or more variable capacitance elements 7, 8 whose capacitance is a function of voltage so as to modify the tuning of the receiver. As shown the code on the punched card or tape 13 is translated by reader 12 into electrical signals which as well as being fed to the converter 11 are fed to a gate or gates 14. These gates control switching circuits 15 which modify via 16 and 17 the IF and scanning circuits according to the line standard, e.g. 625, 819 lines; positive or negative modulation, selected by the appropriate code or the tape 13. The variable capacitance diodes 7, 8 control the oscillator 3 and the high frequency input stage 2 which includes filters or lines for frequency selection and the mixer 3 feeds the video circuits of the receiver via an IF stage 5. Reader and dial.-Photodiodes (D1-D6 and D o  Fig. 5, not shown), controlling the digitalanalogue converter H and gates 14 respectively are energized from a lamp (56) via the punched card or tape 53 which has the channel number (such as 25, Fig. 6, not shown) marked on it and is visible through an opening (59). The photodiodes are mounted in a plastics member (52) and a reflecting coating (57) is provided on a wall of the recorder so as to increase the illumination from the lamp. The code may be made on plastics tapes or cards having transparent and opaque parts instead of perforations. Several channels may be coded on a continuous tape (Fig. 7, not shown), so that by rotating a wheel (72) the required part of the tape is positioned within the reader (74) which has an aperture through which the number of the channel selected can be read. A number of punched cards may be mounted on a rotary device so that the required card may be successively and automatically moved by a button or keys. Digital-analogue converter and fine tuning.-A number of photosensitive diodes each connected in parallel with a resistor are connected to form a series string (Fig. 3, not shown) connected to the base of a transistor (T). When a photo diode is energized by light its resistance becomes zero and shorts the resistor connected across it so that the voltage applied to the transistor is varied depending on the number of diodes energized. By selecting the values of the resistors (R1-R32) appropriately the desired code can be obtained so that an output (V s ) similar to a staircase wave (Fig. 4, not shown), is obtained for varying the voltage applied to the variable capacitance diodes 7, 8. The gain of the converter transistor (T) and hence the fine tuning of the receiver is adjusted by a variable emitter potentiometer (P). The digital-analogue converter may be formed as an integrated circuit.