The Influence of Amplitude Limiting and Frequency Selectivity upon the Performance of Radio Receivers in Noise

This paper describes an experimental study of the relations which exist between the effectiveness of voice communication, measured in terms of the intelligibility of received speech, and the amplitudeand frequency-selective characteristics of amplitude-modulation receivers. The results lead to the following conclusions: (1) Amplitude limiters are ineffective against fluctuation noise. Against impulse noise, however, they provide marked improvement in performance if they are incorporated in receivers with appropriate selectivity characteristics. (2) When no limiter is used, best performance in the presence either of fluctuation noise or of impulse noise is provided by narrow-band circuits, but the advantage of narrow-band circuits over wide-band circuits is small. (3) When a limiter is used, best performance against fluctuation noise is again provided by narrow-band circuits, and again the advantage of narrow-band circuits over broad-band circuits is small. For optimal reception in the presence of impulse noise, however, the selectivity curve of the circuits preceding the limiter must have gradually sloping skirts. When a limiter is used, therefore, advantage rests with broad-band rather than with narrow-band circuits.