A 60-Hz Harmonic Eliminator

A 60-Hz harmonic eliminator has been designed to remove dc and 60-Hz line frequency and its harmonics. By triggering a 1024-point sliding average on each cycle of the line voltage, the harmonics of 60 Hz and dc are averaged from the input. This average is then substracted from the input to eliminate these components, leaving the rest of the signal unaffected. The circuit is equivalent to 500 notch filters at every harmonic of 60 Hz with each notch about 48 dB deep and less than 2 Hz wide.