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Demodulation is the recovery of the useful signal in the baseband that has previously been modulated onto a carrier .

For this purpose, depending on the type of modulation and the occupancy of the frequency band with parallel transmissions, knowledge of certain parameters of the carrier (e.g. frequency , phase angle ), the modulation (e.g. modulation index ) and the useful signal ( bandwidth , possibly Symbol rate ) is necessary. A single message is sufficient for stable parameters, less stable parameters must be determined from the received RF signal. Remaining parts of the wearer, pilot tones and zero symbols help .

The useful signal in the baseband can be represented differently in the receiver than in the transmitter, for example as a profile of a pulse duty factor or sequence of binary coded numbers instead of a voltage profile .

Circuits for demodulation are called demodulators . Circuits that contain both a modulator and a demodulator are called modems for short.

For history , meaning and procedure, see modulation .

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