In an AM communication system, which component recovers the original message from the modulated carrier?

In an AM communication system, which component recovers the original message from the modulated carrier?

• A. Detector
• B. Discriminator
• C. Limiter
• D. Mixer

Answer: (A)

In AM, the information is carried in the carrier’s envelope, so recovering the original message requires an envelope detector. An envelope detector uses a diode to rectify the received RF, producing a pulsating signal whose envelope matches the amplitude variations caused by the modulating signal. An RC network then filters that pulsating waveform, smoothing it so the output follows the slow changes of the envelope, which are proportional to the original message m(t). In short, the detector converts the amplitude variations of the RF carrier into the baseband signal you want to hear. A discriminator, by contrast, is used for FM demodulation to recover information from instantaneous frequency changes, not from amplitude. A limiter is used to constrain amplitude (often in FM paths or to control over-modulation effects) and isn’t what extracts the AM message. A mixer shifts frequencies in the receiver front end, not to recover the baseband content in AM.

In AM, the information is carried in the carrier’s envelope, so recovering the original message requires an envelope detector. An envelope detector uses a diode to rectify the received RF, producing a pulsating signal whose envelope matches the amplitude variations caused by the modulating signal. An RC network then filters that pulsating waveform, smoothing it so the output follows the slow changes of the envelope, which are proportional to the original message m(t). In short, the detector converts the amplitude variations of the RF carrier into the baseband signal you want to hear.

A discriminator, by contrast, is used for FM demodulation to recover information from instantaneous frequency changes, not from amplitude. A limiter is used to constrain amplitude (often in FM paths or to control over-modulation effects) and isn’t what extracts the AM message. A mixer shifts frequencies in the receiver front end, not to recover the baseband content in AM.