NL125/NL126 Digitimer Filter Module

The NL125/NL126 Filter Module employs two active sections to control the variable high-and low- pass characteristics along with a mains frequency Notch filter. It is a combination- replacement for both the NL125 and NL126.

The low frequency cut-off point can be set continuously from 0.5Hz to 5kHz with a single turn potentiometer, in four switched ranges. Similarly the high frequency cut-off can be set continuously from 5Hz to 50kHz in four switched ranges. DC and WB (wide band) switch positions by-pass the lower and upper filter sections, respectively.

The unit has two active notch filters which provided for the rejection of line frequency interference; this is selectable on the board, by the user, as either 50Hz (as the original NL125) or 60Hz (as the original NL126), with a 20Hz notch width (-3dB points).

The LF-CUT (High-pass) filter has a rotary switch that selects the 4 frequency settings and a continuous, calibrated control gives adjustment over that range. This gives a wide range with 12dB/octave [40dB/decade] attenuation below the selected frequency value. The 'DC' switch position by-passes the filter sections completely.

The HF-CUT (Low-pass) filter has a rotary switch that selects the 4 frequency settings and a continuous, calibrated control gives adjustment over that range. This gives 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.