Low-frequency self-tuning filter using analogue-computer components

A method of introducing self-tuning features in a filter with the characteristics of an LCR tuned circuit built up of analogue-computer components is described. The filter is suitable for low frequencies. Tracking and search facilities can be readily incorporated. In an experimental arrangement, the filter could search and track a signal over a range of frequencies in the ratio of 1:10, and a Q factor of 20 was obtained. Applications to Doppler radar-frequency measurements are envisaged.