What may happen if a transmitter is operated with the microphone gain set too high?

When a transmitter's microphone gain is set too high, the output signal is likely to become distorted. This distortion occurs because a high gain amplifies not only the intended audio signal but also any noise or unwanted sounds. As the amplifier reaches its limit, the waveform of the audio signal can clip, leading to a loss of clarity and fidelity in the transmitted signal. In essence, instead of a clear and intelligible audio transmission, a distorted signal is produced, which can lead to misunderstandings in communication.

Other scenarios outlined in the choices, such as output power becoming too high or variations in frequency, may not directly result from merely adjusting the microphone gain. Instead, output power is determined by other factors within the transmitter settings and components. Although SWR (standing wave ratio) could potentially be influenced by antenna mismatch, it is generally not directly related to microphone gain settings. Thus, focusing on the impact on signal clarity illustrates why distortion is the correct consequence of setting microphone gain too high.