How does a diode envelope detector function?

A diode envelope detector is a simple, classic circuit used to demodulate Amplitude Modulated (AM) signals. It works by first passing the incoming AM radio frequency (RF) signal through a diode, which rectifies the signal by allowing only one half of the AC waveform to pass. This process leaves a pulsating direct current whose peak amplitude follows the shape, or "envelope," of the original modulating audio. After rectification, a simple low-pass filter, typically consisting of a capacitor and a resistor, smooths out the high-frequency RF pulses. The capacitor charges to the peak of the RF pulses and discharges slowly enough to track the audio envelope but fast enough not to distort it, leaving only the recovered audio signal. Other options are incorrect because they describe different phenomena. Zener breakdown is used for voltage regulation, not envelope detection. Mixing signals with noise or sensing reactance changes have nothing to do with the fundamental rectification and filtering process of an AM detector.