Demod

Demod, short for demodulation, is the process of extracting the original information-bearing signal from a modulated carrier. It is a fundamental operation in communications, enabling receivers to recover audio, video, or data that was encoded by a transmitter through modulation.

In analog systems, demodulation depends on the modulation scheme. Amplitude modulation (AM) uses an envelope detector to recover the baseband signal. Frequency modulation (FM) is demodulated with a frequency discriminator or a phase-locked loop. Phase modulation (PM) is recovered by differentiating phase changes or by PLL-based methods.

Digital demodulation handles modulated symbols such as BPSK, QPSK, and QAM. It often requires coherent detection with carrier and timing synchronization, followed by symbol decisions. Non-coherent schemes exist when phase information is unavailable. Modern receivers, including software-defined radios, perform digital demodulation in software or hardware using matched filters, decision devices, and equalizers.

Demodulation faces challenges from noise, distortion, multipath, and Doppler effects, which necessitate synchronization and error-correcting codes to improve reliability. Demodulators are implemented as hardware blocks in radio front-ends or as software routines in SDRs.

The term demod is commonly used as shorthand for the demodulation process or for the demodulator component in documentation and designs.