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The Models 751 A, 752A and 753A are programmable Brickwall™ Filters offering near-ideal passband and stopband characteristics. The instruments employ 7th-order (7 poles and 6 zeroes) Elliptic or Cauer filters with design values of0.3dBpeak- to-peak passband ripple and 85 dB stopband attenuation. The transition from passband to stopband has a 115 dB/octave rolloff rate. For low pass response, the stopband is at 1.7 x cutoff frequency; high pass response, the stopband is 0.6 x cutoff for frequency. The cutoff frequency may be programmed from 10 Hz to 99 kHz with 2-digit resolution and 1 Hz to 9 Hz with 1-digit resolution. Pre-filter, and (where available) postfilter gain may be programmed in 10 dB steps, up to the maximum available. These instruments are extremely valuable in signal- processing applications for band-limiting prior to sampling to prevent aliasing, or for separating a narrow spectrum of interest from noise or other interfering signals. In addition to the extremely Sharp filtering, they provide programmable low noise amplification for applications involving low-level signals and overload indicators to ensure operation within their linear dynamic range. The basic differences of the three models are summarized here. Model 753A is a dual-channel instrument which consists of independent high-pass and low-pass sections. The two sections may be used independently, cascaded for band pass response, or paralleled for band reject response. Each section has prefilter gain of up to 40 dB and input overload indicators. The low-pass section has selectable ac/dc input coupling.