Patent GB-1391457-A (GB)
Title: Circuit arrangement for changing the resonant frequency of an  electrical oscillatory circuit by means of one or more diodes
IPC: H03J5/02
Filed: 1972-02-18
Abstract: 1391457 Preset tuning circuits; digital-toanalogue converters GRUNDIG EMV 18 Feb 1972 [18 Feb 1971 (2) 9 March 1971 26 March 1971] 7588/72 Heading G4H [Also in Division H3] In a circuit arrangement for changing the resonant frequency of an electrical oscillatory circuit by means of range-changing diodes controlled by switching voltages and/or by means of a tuning capacitance diode of which the capacitance may be varied by means of switched, pre-adjusted tuning potentials, the range-changing diodes receive their switching voltages and/ or the capacitance diode its tuning potential by way of electronic switches consisting of switching transistors 11-30 to the base electrodes of which control voltages are applied from a electronic stepping switch 2. Each switching transistor 11-30 has its emitter-collector path connected between a respective source of adjustable tuning potential and an electrode of the tuning diode or between a common source of switching potential and an electrode of one of the range-changing diodes. Impulses applied at 1 cause the electronic stepping switch 2 to step so as to sequentially turn on pairs of switching transistors 11, 21-20, 30. The stepping switch 2 includes an impulse counter 3 and a binary-decimal converter 4 which automatically returns from its last condition to its first. The switching transistors 11-20 selectively connect tuning voltages preset by potentiometers 31-40 to a variable capacitance diode of a television receiver connected to 6. Similarly the transistors 21-30 selectively connect 8, 9, 10, as determined by a band switch 51-60, to switching diodes for waveband switching. If not all the switching transistor positions available are required, by switching one of the switches 51-60, such as 53, when the switching transistor 23 is selected by the stepping switch 2 the connection provided by switch 53 to the reset input 5 of the impulse counter 3 resets the stepping switch 2 to select transistors 11 and 21 at the first position. The frequency selected is indicated by illumination of a digital or character display tube 94. The tuning arrangement may also be used in transmitters and signal generators. In a modification (Fig. 2, not shown) in which the outputs (91) of the binary-digital converter 4 control the switching transistors 11-20 and 21-30 as above touch operated tuning and remote control is provided. The remote control may be ultrasonic or radio and provides impulses via an OR gate (101) to operate the stepping switch 2. When a contact 71-80 is touched by a finger the hum voltage received by the associated inverting amplifier (81-90) is applied to an input of a NAND gate (99) and a binary/digital comparator (100). The output of the NAND gate (99) is applied via an inverting amplifier (98) to the strobe input of the comparator (100), the output from which is applied via an inverting amplifier (97) and an OR gate (101) to the input of the counter 3. The counter 3 is stepped on in synchronism with the mains until the numerical setting of the counter 3 corresponds with that of the decimal number appropriate to the contact (71-80) touched. This is obtained by comparing the outputs (ABCD) of the counter 3 and this decimal number in the comparator (100). Reference has been directed by the Comptroller to Specification 1,208,849.