Demodulation is the process of extracting information from a modulated signal. A carrier wave carries data by changing its amplitude, frequency, or phase. Demodulation reverses the process. It recovers the original information. It is the second half of modulation. Together they make communication possible.

The demodulator is part of every receiver. A radio demodulates AM or FM signals. A Wi-Fi chip demodulates OFDM signals. A phone demodulates cellular signals. The demodulator must know the modulation scheme. It must filter out noise. It must synchronize with the carrier.

Demodulation techniques

• Envelope detector: simple AM demodulation
• Phase-locked loop: FM and PM demodulation
• Quadrature demodulator: QAM and digital schemes
• Fast Fourier transform: OFDM demodulation

Demodulation is harder than modulation. The receiver must recover a weak signal that has been attenuated and distorted. It must correct errors. It must handle interference. The better the demodulator, the more data can be recovered from a noisy signal. It is the unsung hero of every wireless link.