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[quote:d61b0e4278=”RadioheadC”]I was under the impression that overmodulation would be contrary to FCC rules, which is why stations have limiters in the audio chain to prevent overmodulation. On the technical side I believ that overmodulation would send the signal farther out and possibly accross adjacent channels.[/quote:d61b0e4278]
Amplitude modulation by positive-going audio peaks can exceed 100% without causing excessive adjacent channel interference. It is only the negative-going peaks that cannot exceed 100% — which will cause interference.
AM broadcast stations typically use audio processors that create or enhance the asymmetry in the peaks of the audio waveform. The negative-going peaks modulate the transmitter to 100% negative modulation, and the positive-going peaks to 125% modulation (the FCC maximum permitted).
These processors also raise the average value of the audio waveform, because the average value is what determines subjective “loudness” in an audio waveform.