GB1309212A - Tunable resonant circuit - Google Patents

Abstract

1309212 Printed circuits; tuning resonant lines RCA CORPORATION 19 April 1971 [23 March 1970] 24181/71 Headings H1R and H1W [Also in Division H3] A tuner comprises a substrate 91 on which components are mounted, the substrate being fabricated of 85% Al 2 O 3 and a 15% mixture of calcium oxide, magnesium oxide and silicon dioxide and has conductive a pattern of silver and glass fused thereon which is covered by copper plating, a moistureproof silicon layer being applied to the complete substrate and pattern except for bonding areas of the conductive layer. The components are soldered to the bonding areas. The substrate is mounted within a box with detachable side covers 99, one of which has a screen 550 attached thereto which lies over tuning circuits. The R.F. amplifier of the tuner is built on one side of the substrate with a corresponding ground plane 93 (Fig. 4) on the opposite side thereof and the oscillator circuit is built on said opposite side with its corresponding ground plane 95 (Fig. 5) on said one side so providing screening between the stages. The stages are each tuned by transmission lines each comprising two sections 67a, 67b (Figs. 1, 5) over a ground plane, the sections and ground plane being disposed on opposite sides of an insulating substrate and the two sections 67a, 67b being joined and tuned by a reactance 75 whose value depends on the applied voltage thereto. As shown in Fig. 1, the reactance is a diode whose capacitance varies with applied voltage. Two such transmission lines 69a, 69b and 71a, 71b may be coupled by inductors 106, 108 to form a filter which is tuned by diodes 79, 83 controlled by a voltage source 175 via resistors 178, 180, 182. The sections 67b, 69b, 71b are curved exponentially to predetermine the change of reactance with frequency of the lines. Inductances 77, 81 and 85 may be included to affect coarse tuning of the lines (Fig. 10). Tapers on the corners of the line sections 67a, 69a, 71a, 73a compensate for fringing of the electromagnetic and electrostatic fields at the section ends. Details of the tuner and oscillator are described and claimed in Specifications 1,309,211 and 1,309,213 respectively.