AMdemodulaatiojärjestelmissä

AM demodulaatio is the process of extracting the original information signal from an amplitude-modulated (AM) radio wave. Amplitude modulation involves varying the amplitude of a carrier wave in proportion to the instantaneous amplitude of the message signal. To recover the original message, the received AM signal must be demodulated.

Several methods exist for AM demodulation, with the most common being envelope detection. This technique relies on the fact that the envelope of the AM signal directly follows the waveform of the original message. An envelope detector typically consists of a diode and a low-pass filter. The diode rectifies the incoming AM signal, allowing only one half of the waveform to pass through. The capacitor in the filter then charges up to the peak amplitude of the rectified signal and discharges slowly, effectively smoothing out the carrier frequency and leaving behind a signal that approximates the original message. A resistor is also part of the filter circuit to allow the capacitor to discharge.

Another method is synchronous demodulation, also known as coherent detection. This technique requires a locally generated carrier wave that is synchronized in both frequency and phase with the received carrier wave. The incoming AM signal is multiplied by this local carrier. If the carriers are perfectly synchronized, the output of the multiplier will contain the original message signal, along with sum and difference frequency components. A low-pass filter is then used to remove the unwanted frequency components, leaving only the desired message signal. Synchronous demodulation offers better performance, particularly in the presence of noise, but is more complex to implement than envelope detection because it requires carrier synchronization circuitry.