Demodulatsioon

Demodulatsioon is the process of extracting the original information signal from a modulated carrier. In communications, modulated carriers convey information by varying one or more properties of a carrier wave (amplitude, frequency, or phase) according to the input signal. Demodulation converts the received signal back into a form suitable for interpretation by the receiver. Demodulation can be analog or digital, and can use coherent or non-coherent detection.

Analog demodulation methods include envelope detection for amplitude modulation (AM), product detection for suppressed-carrier AM, and discriminators or phase-locked loop–based discriminators for frequency modulation (FM) and phase modulation (PM). For AM, the envelope detector recovers the modulating signal by rectifying and filtering the carrier envelope; for double-sideband suppressed-carrier AM, a coherent demodulator multiplies by a locally generated carrier. For FM and PM, demodulation often uses a phase-locked loop or a quadrature detector to convert instantaneous frequency or phase deviation into a voltage proportional to the modulating signal. Digital modulations like quadrature amplitude modulation (QAM), phase-shift keying (PSK), and frequency-shift keying (FSK) require digital demodulation, including sampling the received waveform and performing symbol synchronization, channel estimation, and decision logic.

Receiver chains include downconversion to baseband or intermediate frequency (IF), filtering, amplification, and sampling, followed by demodulation and digital signal processing. Demodulation performance is affected by noise, interference, channel distortion, timing errors, and nonlinearity. Proper synchronization of carrier phase, frequency, and symbol timing is critical for coherent demodulation.

Applications span radio receivers, television, mobile and satellite communications, and data networks. Demodulation is a fundamental step in the end-to-end process of converting transmitted data into usable information.