Which statement correctly differentiates a carrier signal from a modulating baseband signal?

• A. Both the carrier and the baseband operate at the same frequency.
• B. The baseband signal is the high-frequency carrier; the carrier carries information.
• C. The carrier is a high-frequency sinusoid; the baseband signal carries the information and modulates the carrier.
• D. The baseband signal is typically sinusoidal at the same frequency as the carrier.

Answer: (C)

The essential idea is that a carrier provides the high-frequency vehicle for transmission, while the baseband carries the actual information and modulates that carrier. In communication systems, you generate a high-frequency sinusoid—the carrier—and use the information-laden signal, which lives at much lower frequencies (the baseband), to alter some property of the carrier (its amplitude, frequency, or phase). This modulation creates a new RF signal that can be transmitted efficiently over distances. The baseband signal itself does not need to be at high frequency; it is the information source, and it modulates the carrier so the information can be recovered at the receiver.

Why this option fits best: it states that the carrier is a high-frequency sinusoid and that the baseband carries the information and modulates the carrier, capturing both roles accurately.

Why the others don’t fit: the baseband is not at the same high frequency as the carrier, nor is it the high-frequency carrier itself; the baseband typically sits at much lower frequencies than the carrier, and modulation is the process that maps that information onto the carrier.