The NL134, NL135 and NL136 are 4-channel, 2-pole (second order) low pass filters. Both the NL135 and NL136 have an AC power rejection notch filter module that is an ideal partner for the NL820A Isolated Amplifier System with its 2/4 channel AC or DC pre-amplifiers.
The filter settings have been selected for most electrophysiological and clinical protocols but other frequencies can be factory set to order. The design is implemented using low noise active linear circuitry and does not suffer any of the aliasing problems that are encountered when cheaper methods are used.
A rotary switch selects the 14 frequency settings giving repeatability over a wide range with 12dB/octave [40dB/decade] attenuation above the selected frequency value. The 'WB' (wide-band) switch position by-passes the filter sections completely (both LP and Notch). The active Notch filter provides rejection of line frequency [50Hz (NL135) or 60Hz (NL136)] interference when switched in. (No switch is fitted on the NL134).
The NL144 is a high-pass version and does not have a notch filter. Preset factory filter settings span from 0.1 to 200 Hz in 1-2-3-5 steps.