D **14.30 (a) For a second-order notch function with ωn = ω0, show that for the attenuation to be greater than A dB over a frequency band BWa, the value of Q must satisfy
(Hint: First, show that any two frequencies, ω1 and ω2, at which | T | is the same, are related by ).
(b) Use the result in (a) to find the transfer function of a notch filter that is required to eliminate a bothersome interference of 60-Hz frequency. Since the frequency of the interference is not stable, the filter should be designed to provide attenuation ≥ 20 dB over a 6-Hz band centered around 60 Hz. The dc transmission of the filter is to be unity.