The waveforms on the right illustrate the effectiveness of the noise blanking. The impulse noise was induced in the receiverfrom a noise pulse generator.
The waveforms in the left column are of the noise at various points within the receiver with the noise blanker turned off. The waveforms in the right column show the signals at the same points with the noise blanker turned on.
The waveforms in the top row picture the noise at the input to the IF strip. The points within the IF strip progress down the column and toward the last stage in IF strip at the bottom where the detected output that is applied to the audio amplifier.
The small amount of low frequency noise in the bottom right pictures shows residual noise that is at a frequency too low to hear.
The impulse noise levels were produced by the ringing of the Collins mechanical filter and were obviously destructive in the presence of impulse noise. Such ringing is typical for high-Q resonant circuots within the filter (poles) that is necessary to produce the steep skirts of this filter. This works well for rejection of adjacent channel signals, but can be highly destructive in the presence of impulse noise. It was later discovered that the steep skirts of the Collins mechanical filter were not essential, and it was replaced by another mechanical filter designed to produce a less steep falloff.
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