Noise-spectrum measurement at subaudio frequencies

Direct measurement of noise spectra requires a standard-noise generator, a narrowband filter of adjustable frequency and a detector of adequate integrating time. Instruments for performing these three functions in the subaudio range of frequency are described. The accuracy is assessed, and it is shown that a high degree of precision is attainable. An example is included of the use of these instruments for the measurement of the flicker noise spectra of transistors.