What is the primary effect of modulation on a carrier signal?

The primary effect of modulation on a carrier signal is to vary its amplitude, frequency, or phase. Modulation is a fundamental technique used in communication systems to encode information onto the carrier signal. By altering one or more characteristics of the carrier wave—such as its amplitude (AM), frequency (FM), or phase (PM)—the information can be transmitted over long distances without significant degradation.

Each type of modulation serves a specific purpose and is chosen based on the requirements of the communication system, such as bandwidth efficiency, power efficiency, and resilience to noise. For example, frequency modulation is less susceptible to noise, making it useful for high-fidelity audio broadcasts.

The other options do not accurately capture the essence of modulation. Maintaining a constant amplitude does not represent modulation since modulation entails changes in the carrier signal to convey information. While modulation can help with noise resistance, its primary purpose isn't to eliminate noise. Furthermore, while modulation can be part of a broader system that includes encryption, its primary function is not to encrypt the signal but to encode the information being transmitted onto the carrier. This understanding of modulation is essential for anyone studying communication technology and systems.