The Model 4-NB is a solid-state noise blanker for use with the R-4C Receiver. 

Unlike noise clippers or limiters commonly found in communications equipment, the 4-NB is an advanced noise blanker which actually mutes the receiver for the duration of the noise pulse. 

Between noise pulses, full receiver gain is restored. 

Receiver AGC is affected only by the desired signal and not by noise. 

The 4-NB is most effective on strong, periodic impulse noise such as ignition noise. It is least effective on random noise. Random noise is continuous in time and the information it masks cannot be recovered by either blanking or limiting techniques.