Demodulaatiomenetelmät

Demodulaatiomenetelmät refer to the techniques used in telecommunications to recover the original information signal from a modulated carrier wave. This process is the inverse of modulation, where information is embedded onto a carrier signal for transmission. Demodulation is a crucial step in receiving and interpreting the transmitted data.

Several demodulation methods exist, broadly categorized based on the type of modulation used. For amplitude modulation (AM), envelope detection is a common technique. This method uses a simple circuit with a diode and a capacitor to extract the envelope of the modulated signal, which corresponds to the original message. Synchronous demodulation, also known as coherent demodulation, is another method that requires a local oscillator at the receiver to generate a carrier wave precisely synchronized in frequency and phase with the transmitted carrier. This allows for accurate extraction of the modulating signal.

Frequency modulation (FM) typically employs discriminators or phase-locked loops (PLLs) for demodulation. Discriminators convert frequency variations into amplitude variations, which can then be processed. PLLs are more sophisticated and can track variations in the carrier's frequency and phase, providing a more robust demodulation, especially in noisy environments.

Phase modulation (PM) also utilizes synchronous demodulation or PLLs. In synchronous demodulation, the received signal is multiplied by a locally generated carrier, and a low-pass filter removes the high-frequency components, revealing the original phase variations.

Digital modulation schemes like amplitude-shift keying (ASK), frequency-shift keying (FSK), and phase-shift keying (PSK) have their specific demodulation techniques. For instance, FSK can be demodulated using filters to separate the different frequencies or by using PLLs. PSK demodulation often involves coherent detection, where the received signal is correlated with locally generated replicas of the transmitted symbols. The choice of demodulation method depends on factors such as the modulation scheme, desired performance, complexity, and cost.