Premodulation Clipping in AM Voice Communication

Articulation tests were conducted to assess the advantages of premodulating clipping in A M voice transmitters. The results show that a saving of as much as 14 decibels in carrier power can be achieved, without loss in intelligibility, if the speech wave is first subjected to 24 decibels of peak clipping and then reamplified by 24 decibels in order to obtain 100‐percent peak modulation. Three obvious advantages result from this procedure: (1) the effective range of a given transmitter is increased, (2) overmodulation is permanently prevented, and (3) interference to communications on adjacent frequency channels is eliminated. Realization of this third advantage requires the introduction of a low‐pass filter between the clipper and the point of modulation. Excessive amounts of premodulation clipping should be avoided whenever speech quality is an important consideration and whenever the microphone picks up large amounts of ambient noise. On the other hand, when communication is impaired by ambient noise and atmospheric static at the receiver location, large amounts of premodulation clipping serve to maximize intelligibility.