GB462447A - Improvements in high frequency electric oscillators - Google Patents

Abstract

462,447. Piezo-electric crystal mountings. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 26, 1936, No. 29057. Convention date, Oct. 25, 1935. [Class 40 (v)] [Also in Group XXXVI] An oscillator for checking the carrier frequencies of radio transmitters or for like purposes is tuned by means of a piezoelectric crystal mounted with a tuned circuit in an interchangeable plug 18 which can be inserted into the oscillator. The anode circuit 19, 22 is tuned slightly above the desired frequency, and the frequency is precisely regulated during manufacture by adjusting the relative positions of the crystal cell 20 and coil 19, so as to vary the extent to which the metal electrodes of the cell lie in the magnetic circuit of the coil. The coil 19, Fig. 2, is preferably annular and the crystal cell 20 is soldered to leads 23 which pass through hollow plugs 13 so that the position of the crystal cell can be adjusted by manipulating the leads, which are soldered to the lower ends of the hollow plugs when the frequency is correct. The plane of the cell may be at right angles to that of the coil for the higher frequencies, but for the lower frequencies the cell may be parallel to the coil so that its metallic parts lie to a greater extent in the magnetic field of the latter. A condenser 22 may be shunted on the coil for the lower frequencies but omitted for the higher frequencies. The parts are fixed in position by filling the container 18 with a sealing compound, or for the higher frequencies with rock wool (in order that the filling may not affect the frequency). The crystal cell 20 comprises metallic electrodes 21, Fig. 3, an insulating annulus 25, a crystal 26 with floating electrode 27, and a crow-foot spring 28 for fixing the crystal and making electrical connection.