What does AM stand for and what does it do?

• A. Amplitude Modulation
• B. Frequency Modulation
• C. Phase Shift Keying
• D. Amplitude Shift Keying

Answer: (A)

Amplitude Modulation means you vary the carrier signal’s amplitude in proportion to the input information, while the carrier’s frequency and phase stay essentially fixed. As the information signal changes, the envelope of the RF wave rises and falls accordingly, producing the carrier plus sidebands that actually carry the content. A receiver recovers the original signal by extracting that envelope, typically with an envelope detector in analog AM radios. This method is simple to implement and widely used for traditional analog broadcasting, but it isn’t very power-efficient because a lot of the transmitter power sits in the unmodulated carrier, and the signal is more prone to noise that modulates amplitude. The other options describe different ideas: varying frequency (not amplitude) for the modulation, changing only the phase, or altering amplitude in discrete steps for digital amplitude-shift-keying, which is a different kind of modulation.