INTRODUCTION The Model 30A Series are low-pass, 7-pole, 6-zero elliptical plug-in filters providing 115dB/octave roll-off, a minimum stopband attenuation of >80dB, and a typical passband ripple of 0.22dB peak-to-peak. The Model 30A-1 covers the range from 1Hz to 99kHz. The Model 30A-2 operates from 0.1Hz to 9.9kHz and from 0.01Hz to 990Hz in the Model 30A-3. With its 115dB/octave rolloff rate, the Model 30A provides a much narrower transition region than an 8-pole Butterworth, and much less passband attenuation near cutoff. The transition region from –3dB to –85dB is 64% of fc (cutoff), compared to 242% for the 8-pole Butterworth. From –0.3dB to –85.6dB, it becomes 70% of fc compared to 404%. This permits lower sampling rates and wider bandwidths, resulting in lower total system costs. The Model 30A Series is part of an ever expanding line of plug-in filter cards for use in the Model 3905C and 3916C Mainframes, which accommodates 5 to 16 filter cards respectively.