Improved self-tuning filter for low frequencies

An improved method for introducing self-tuning features in an active filter for detection of weak signals in a noisy background is described. The filter, which works at low frequencies (100 Hz¿10 kHz), is provided with facilities for search and tracking. During an experiment, the filter was able to detect a sinusoidal signal of 1 mV r.m.s. in a 10 kHz-bandwidth background noise of 3 mV r.m.s.