An elliptic filter design for the Space Shuttle vibro-acoustic experiment

An elliptic filter is presented whose purpose is to detect an impending launch by listening for a 600-Hz tone characteristic of the auxiliary power units (APUs). These are activated between five and ten minutes prior to launch. The filter comprises the key element in an APU detection circuit, and it is implemented using a pair of generalized impedance converters (GIC) in cascade. The GIC configuration is highly insensitive to changes in both its passive and its active parameters, is capable of implementing a large variety of biquadratic filter functions, and is thus an excellent choice for active filters. The two GIC sections represent biquadratic factors which individually implement a high-pass and a low-pass notch filter. When placed in cascade, the result is a very narrow band elliptic filter. This paper includes measurements of the sensitivity of the filter to changes in its parameters