GB668391A - Improvements in or relating to piezo electric crystal oscillators - Google Patents

Abstract

668,391. Valve generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Feb. 7, 1950 [March 30, 1949], No. 8671/49. Class 40 (vi). In a piezo-electric crystal oscillator circuit the crystal is coupled to the driving valve over a line three-quarters of a wave-length long, the grid of the valve being connected to a point a quarter, and the anode at a point three-quarters of a wavelength from the crystal, or vice versa. The line may be artificial and may have uniform constants or be of the " tapered " type; it is stated that shunt elements adjacent the crystal or half-a-wavelength away are not critical in value and may be omitted. A resistance shunted across either of these points in the line serves to suppress unwanted modes of oscillation, while the desired frequency may be adjusted over a limited range by means of a variable impedance between the cathode and either grid or anode of the valve. Networks suitable for the purpose are described in the Specification, and include a tapered low-pass filter, Fig. 2, in which the crystal is connected across points 1, 2 and the grid, anode and cathode of the valve to points 3, 4, 5, respectively. Alternatives comprise the corresponding high-pass filter, Fig. 3 (not shown), and various derived networks of mixed type utilizing both low- and high-pass sections, Figs. 4-7 (not shown).