*Question G4C04:
What sound is heard from an audio device experiencing RF interference from a CW transmitter?*  

*Correct Answer is  A: On-and-off humming or clicking*  

### AI Response: (may contain errors)  

When an audio device experiences RF interference from a Continuous Wave (CW) transmitter, the sound produced is typically an on-and-off humming or clicking. Let's break down the reasoning behind the correct answer and why the other options are incorrect.

### Correct Answer: A - On-and-off humming or clicking
- **Explanation**: 
  - CW transmitters emit a signal that is either on or off, corresponding to the Morse code being transmitted. When this signal interferes with an audio device, it can cause the device to pick up the rapid on-off nature of the CW signal, resulting in a sound that resembles a humming or clicking noise. This is due to the modulation of the RF signal affecting the audio output.

### Why the Other Choices are Incorrect:
- **B - A CW signal at a nearly pure audio frequency**:
  - This choice suggests that the interference would produce a clean CW tone at an audio frequency. However, CW signals are not modulated to produce audio frequencies; they are simply on-off keying of a radio frequency. The interference would not produce a pure tone but rather a more erratic sound.

- **C - A chirpy CW signal**:
  - A chirpy signal implies a variation in frequency, which is not characteristic of a CW transmission. CW signals are constant in frequency, and any chirping would indicate modulation or frequency changes, which is not typical of RF interference from a CW transmitter.

- **D - Severely distorted audio**:
  - While RF interference can cause distortion, the specific nature of CW interference typically results in a more rhythmic on-and-off sound rather than severe distortion of the audio signal. Distortion would be more associated with other types of interference, such as from AM signals or other modulated signals.

### Summary
- The correct answer is based on the nature of CW signals and how they interact with audio devices. The on-and-off nature of the CW signal leads to the characteristic humming or clicking sound, while the other options misinterpret the effects of RF interference from a CW transmitter. 

This understanding is crucial for recognizing the types of interference and their effects on audio devices, which is a common topic in the Extra Class exam.