Took a few seconds of the signal from Droitwich with speech modulation,
downconverted to 0 - 6kHz and saved as a .WAV file.
I already had some software that analyses a .WAV file for maximum and
minimum peaks, calculates the RMS and some other analysis functions not
relevant here. The Droitwich recording showed maximum positive and
negative peaks (amplitude, not power) in the region of 6600 (out of 32786
maximum) and an RMS value of 2995, giving a peak to mean ratio of 6.9dB.
(technically, peak to RMS, but in power terms equal to peak to mean)
Bear in mind that this peak amplitude was the highest single one recorded in
several seconds of audio. To compare, a sinewave has a 3dB peak to mean
and this software does give exactly that figure for a .WAV test file
containing a pure sinewave.
A 'perfect' 100% modulated AM transmission carrying a sinewave should have
4.8 dB peak to mean, so what mechanism can account for 6.9dB ? This
certainly does seem to reinforce the idea that the carrier reduces with
amplitude.
Andy G4JNT
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