Abstract :
The paper describes the quartz-crystal control arrangements for a radio transmitter designed to radiate a standard frequency of 1785 kilocycles per sec. The special feature of the quartz oscillator is its mode of support. It rests on four pins screwed into holes drilled into the edges of the oscillator in its nodal plane. By the use of this method of mounting the damping of the oscillator is decreased, and frequency-changes due to movement between the electrodes are nearly eliminated. The quartz plate was tested as a resonator, and its edge was ground until one strong resonance was obtained well removed from neighbouring resonances. It was then found to give a good performance as an oscillator. Tilting the mounting produced a maximum frequency-change of 2 parts in 106, and the frequency varied linearly with temperature and smoothly with air-gap. The frequency was adjusted to 1785 kilocycles per sec. The feeble oscillations of the crystal were amplified in two transformer-coupled stages and were then fed to the power valves of a transmitter. Changes of 5 per cent in the tuning of the amplification and power stages produced frequency-changes of only a few parts in 107. The frequency of the transmitter showed a stability of 1 part in 107 over short periods and 1 part in 106 from day to day. A small condenser connected between the grid and the plate of the valve driving the crystal enabled the frequency of oscillation to be adjusted so that it could be maintained at a value within 1 part in 107 of that of the standard tuning-fork.
