Which statement correctly describes analog modulation and digital modulation?

• A. Digital modulation encodes discrete bits on a carrier.
• B. Analog modulation varies a continuous signal.
• C. Analog modulation uses discrete symbols on a carrier
• D. Analog modulation varies a continuous signal; digital modulation encodes discrete symbols (bits) onto a carrier

Answer: (D)

Modulation can be categorized into analog and digital types. In analog modulation, the information is carried by continuously varying features of the carrier, such as its amplitude, frequency, or phase, reflecting a continuous-valued input. In digital modulation, the information is represented by discrete symbols or bits that are mapped onto the carrier, creating distinct signal states. The statement that analog modulation varies a continuous signal and digital modulation encodes discrete symbols (bits) onto a carrier is the most accurate because it describes both approaches in one concise idea. The other descriptions are incomplete or mischaracterize digital modulation by implying it uses continuous signals or only describing one type.