A controlled oscillator for generating standard audio-frequencies
Louis Essen · Journal of Scientific Instruments · 1936
A description is given of an audio-frequency oscillator which is controlled by a primary frequency of a constant value, and which provides a series of discrete frequencies between 10 cycles per second and 20,000 cycles per second, the accuracy of which is better than 0.1 part in a million. The standard primary frequency used has been 20,000 cycles per second. It is multiplied to 80,000 cycles per second. This frequency controls the audio-frequency oscillator, providing a series of values represented by 80,000/ n cycles per second, where n is any integer. When it is more convenient one of the series 40,000/ n , 20,000/ n or 1000/ n cycles per second is obtainable.