DNF 1201A Dynamic Noise Filter

Principles of Operation


An incoming signal is sensed by the Bandwidth Controller, which develops a negative DC voltage. The voltage will be dependent on the frequency and amplitude of the signal, as well as teh setting of the SENSITIVITY control. The DC output then controls the variable low-pass filter of each audio channel.

As the B.C. output becomes more negative the filters' cutoff frequency slides upwards. The filters operate anywhere from total suppression (-3dB @ 600 Hz) to wideband (-3dB @ 27kHz). The filter channels can be held in wideband mode by depressing the OUT button which feeds -18vdc into the B.C. Hand-drawn block diagram

(c) 1980 Richard Burwen, posted by permission.

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March 16, 1998