AMdemodulaatio

AMdemodulaatio, also known as amplitude demodulation, is a process used to extract the original information signal from a modulated carrier wave. In amplitude modulation (AM), the amplitude of a high-frequency carrier wave is varied in accordance with the instantaneous amplitude of the modulating signal, which carries the information. To recover this information, the AMdemodulaatio process essentially reverses this modification.

The most common and simplest form of AMdemodulaatio is envelope detection. This method utilizes a diode, which acts as a rectifier, allowing current to flow in only one direction. The AM signal is passed through the diode, effectively clipping off one half of the carrier wave's cycles. Following the diode, a capacitor is used in conjunction with a resistor to form a low-pass filter. The capacitor charges up to the peak amplitude of the rectified RF signal and then slowly discharges through the resistor between the peaks. This filtering action smooths out the rapid fluctuations of the carrier wave, leaving behind a waveform that closely follows the envelope of the original AM signal, which is the desired audio or data signal.

Another, more sophisticated method is synchronous detection, also known as coherent detection. This technique requires a local oscillator at the receiver that is precisely synchronized in frequency and phase with the original carrier wave used for modulation. The incoming AM signal is multiplied with the locally generated carrier. This multiplication process, when the carriers are perfectly aligned, effectively strips away the carrier frequency, leaving the baseband information signal directly. Synchronous detection offers improved performance, particularly in the presence of noise and fading, compared to envelope detection, though it is more complex to implement.