A modulator is an electronic circuit that superimposes a low-frequency (information) signal onto a high-frequency (carrier) signal for the purpose of wireless transmission. The reason for this is that higher frequency signals can be received using shorter aerials, which are more practical than longer ones. The information signal can be either analog or digital.
The modulator circuit superimposes the information signal onto the carrier signal by modifying one of the properties of the carrier, i.e., amplitude, frequency, or phase.
The following table summarizes the main modulation types for each type of information signal.
|Analog||Amplitude Modulation (AM)||Frequency Modulation(FM)||Phase Modulation(PM)|
|Digital||Amplitude Shift Keying(ASK)||Frequency Shift Keying (FSK)||(PSK)|
Once the transmitted signal has been detected and received, a demodulator circuit is then used to recover the information signal from the carrier.