Patent GB-1331625-A (GB)
Title: Frequency selection circuit
IPC: H03J5/02
Filed: 1970-12-18
Abstract: 1331625 Tuning arrangements; transistor gating circuits INTERNATIONAL STANDARD ELECTRIC CORP 18 Dec 1970 [29 Dec 1969] 60108/70 Headings H3Q and H3T [Also in Division G4] A frequency selection circuit comprises a voltage or current controllable RF unit or tuner 1 and a plurality of main switching devices S1, S2, Sn connected in parallel between a first common impedance R2 and a second common impedance R3, each main switching device contains means R12, R22 to restrict the current over that path to a desired value and has the ability to maintain itself operated until a further one of the main switching devices is brought into operation. The voltage to control the RF unit or tuner 1 is developed across the first common impedance R2 in response to current through an operated main switching device and a current through a further main switching device when one device is already operated causes a voltage to develop across the second common impedance 3 which is effective to interrupt the operation of the already operated device Closing a push button switch TS1 turns on bistable circuit transistors T1, T1<SP>1</SP>, Fig. 3, and the tuning voltage set by resistor R12 is applied to voltage variable capacitors D1-D3 of the RF unit of a radio, television or transmitter. Transistors T1, T1<SP>1</SP> remain on until another push button TS2 is pressed which makes transistors T2, T2<SP>1</SP> conduct and the increased voltage across resistor R3 turns off the transistors T1, T1<SP>1</SP> in the previously on electronic switch S1. The tuning voltage at 4 is now that adjusted by R22. Waveband switching may be achieved together with the frequency selection by connecting the control electrodes of the electronic switches S1-S3 via waveband switches (US10, US20, US30, Fig. 2, not shown) to further electronic switches (S10, S20, S30) such as diodes which connect waveband switching voltages to terminals 5, 6, 7 of the RF unit 1. The frequency control may be obtained by electromagnetically susceptable inductors. In order to store the frequency selection of the last key pressed after the radio or television set has been switched off the supply voltage for the electronic switches is maintained. Chargeable batteries arranged in parallel to the supply voltage or capacitors may be used as the storage elements. The store may take the form of electrolytic capacitors connected to the control electrodes of the electronic switches so as to limit the current when the set is off. During the idle period of the set the control electrodes may also be supplied with voltage by electrets. Alternatively automatic selection of a particular frequency may be effected when the set is switched on by mechanically coupling the switch or key of the set with a certain frequency selecting key. This may alternatively be effected by supplying the control electrode of a certain electronic switch with current via a capacitor when the set is switched on. Indication of which electronic switch is operated may be provided by a lamp, a luminescent diode or an electromechanical device. Remote control of the electronic switches may be effected by operating each switch in parallel to the main control unit by signals transmitted over wires or by radio. The remote control arrangement may include touching contacts or devices switching by proximity. The circuits may be constructed in integrated form. (For Figures see next page.)