AM, or amplitude modulation, was the earliest way of sending voice over radio waves. That makes sense because it is easy to modulate a signal and easy to demodulate it, as well. A carbon ...

The difference is in how the carrier wave is modulated, or altered. With AM radio, the amplitude, or overall strength, of the signal is varied to incorporate the sound information. With FM ...

Compared to the simple diode needed to demodulate AM radio signals, the detector circuits ... Since the frequency of the modulated carrier changes, the duty cycle of the resulting pulse train ...