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The interesting part about it is the modulation process takes place in a non-linear mixer.
An audio mixer is a linear device. If faithfully reproduces the signal characteristics while allowing the amplitude to be changed-up to the point of distortion.
An audio mixer can combine or “mix” two or more signals while each signals characteristics are maintained (not counting any EQ or other effects you may employ.)
Unlike AM modulation (Department of Redundancy Department) there are no plus/minus sideband frequencies generated.
When you look at the RF carrier envelope using an ocsilloscope, when modulated the RF carrier appears to change in the positive and negative direction at the same time creating a larger/smaller peak-to-peak value. It appears there is only the carrier changing in amplitude.
When you look at two or more signals combined in an audio mixer using an oscilloscope there is no envelope. Rather a single signal which is the combination of the two or more signals added together. One signal is not impressed on the other or to say one is not modulating the other.
Once the AM carrier is modulated, if you want to boost the power with an amplifier it must be a linear amplifier as you must faithfully reproduce the carrier and sidebands.