A Miniature Variable Capacitor

A two-section variable capacitor of novel design has been developed for use as a tuning element in a microelectronic superheterodyne receiver. The device consists of a ganged oscillator and RF section, both contained in a metallic cylinder 0.25 in. in diameter and 1.125 in. in length. Each section of this capacitor comprises: (1) an electrically grounded conductive screw, (2) a threaded insulating sleeve into which the screw fits, and (3) a conducting material surrounding the sleeve. In a typical capacitor, the capacitance of one section was variable between 0.75 and 8.0 pf and of the other section between 1.5 and 12.0 pf, the Q ranged from 224 at 10 megacycles to 190 at 20 megacycles, and capacitances remained within 1 percent of the set values over the temperature range -60 to + 80°C.