What term is defined as the unmodulated carrier frequency on an FM transmitter?

The term that refers to the unmodulated carrier frequency on an FM transmitter is known as the center frequency. In frequency modulation (FM), the center frequency is the frequency at which the carrier signal operates when no information is being transmitted. This frequency serves as the baseline around which the frequency of the signal varies in accordance with the amplitude of the incoming audio or data signal being transmitted.

When modulation occurs, the frequency of the carrier wave is altered based on the instantaneous amplitude of the input signal; however, when there is no input signal present, it reverts to this center frequency. Understanding the concept of center frequency is essential for grasping how FM transmission works and how the modulation affects the overall signal produced.

The other terms listed, such as modulation index, amplitude frequency, and carrier shift, refer to different concepts within the realm of modulation techniques and signal processing, but none directly indicate the unmodulated state of the carrier frequency like the center frequency does.