modulator

A modulator is a device or circuit that encodes information signals onto a carrier signal by modulating a property of the carrier, such as its amplitude, frequency, or phase. Modulation is fundamental to communications because it allows the transmission of signals over limited bandwidth and through channels with varying characteristics.

A modulator combines a carrier with a baseband or intermediate signal. In analog modulators, the modulating signal causes the carrier's amplitude, frequency, or phase to vary in time. Demodulation at the receiver recovers the original information from the modulated carrier.

Analog modulation types include amplitude modulation (AM), where carrier amplitude follows the information signal; frequency modulation (FM), where carrier frequency changes with the signal; and phase modulation (PM), where carrier phase varies with the signal. Digital modulation uses discrete signal levels, such as amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK); combinations like quadrature amplitude modulation (QAM) encode data in both amplitude and phase. Some systems employ multi-carrier schemes such as OFDM.

Implementation can be analog, using multipliers or mixers and voltage-controlled oscillators, or digital, using DSP or FPGA-based modulators with digital-to-analog conversion. Performance is characterized by metrics such as modulation index or deviation, required bandwidth, and resilience to noise and interference. Demodulation reverses the process to recover the original information.

Modulators are used in radio broadcasting, television, telephone and data links, satellite and wireless networks, radar, and instrumentation systems.