Design of a Portable Temperature-Controlled Piezo Oscillator

This paper describes the essential details of a portable shielded temperature-controlled piezo oscillator constant in frequency to better than one part in 100,000. The quartz plate is mounted in a special plate holder so that the air-gap changes very little as the quartz plate shifts in the holder. The plate holder is mounted in a thermal-attenuating chamber consisting of a copper cylinder and layers of asbestos, contained in a wooden box. The copper cylinder is mounted on heavy bronze coil springs to absorb shocks. A sensitive mercury thermostat, placed in a slot in the side of the copper cylinder, controls the temperature. The heater operates on 110 volts direct current. The quartz plate is connected between the grid and the filament of the oscillator tube. An inductor, having a natural frequency slightly higher than that of the quartz plate, is used in the plate circuit of the tube. The load is kept constant by loosely coupling to the output through a screen-grid radio-frequency amplifier. Measurements on the piezo oscillator give the following results; temperature coefficient of 0.0025 per cent per degree centrigrade change in temperature of the quartz plate itself; 10 per cent variation of plate or filament voltages from operating point of the oscillator tube causes less than 1 part in 1,000,000 change: jarring has no measurable effect on the frequency.