In frequency modulation (FM), which characteristic of the carrier signal is varied to encode the audio?

In frequency modulation (FM), which characteristic of the carrier signal is varied to encode the audio?

• A. Phase
• B. Power
• C. Frequency
• D. Amplitude

Answer: (C)

In frequency modulation, the audio signal changes the instantaneous frequency of the carrier. As the audio varies, the carrier shifts up and down around its center frequency within a fixed maximum deviation, while the carrier’s amplitude stays essentially constant. This means the information is carried by how fast the carrier oscillates (its frequency) rather than how tall the wave is (amplitude) or where its phase sits. The amount of frequency shift is proportional to the audio signal's amplitude, often described by the frequency deviation and modulation index. Because the amplitude remains constant, FM tends to be more resistant to amplitude noise, preserving audio quality after transmission. So, the characteristic varied to encode the audio is the frequency.

In frequency modulation, the audio signal changes the instantaneous frequency of the carrier. As the audio varies, the carrier shifts up and down around its center frequency within a fixed maximum deviation, while the carrier’s amplitude stays essentially constant. This means the information is carried by how fast the carrier oscillates (its frequency) rather than how tall the wave is (amplitude) or where its phase sits. The amount of frequency shift is proportional to the audio signal's amplitude, often described by the frequency deviation and modulation index. Because the amplitude remains constant, FM tends to be more resistant to amplitude noise, preserving audio quality after transmission. So, the characteristic varied to encode the audio is the frequency.