*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 CW (Continuous Wave) transmitter, the interference manifests as an on-and-off humming or clicking sound. Here's why:

1. **Correct Answer: On-and-off humming or clicking (Choice A)**
   - A CW transmitter sends out a continuous wave signal that is either on or off. When this signal interferes with an audio device, it can cause the device to pick up the on-off pattern of the CW transmission. This results in a repetitive humming or clicking sound that corresponds to the keying of the CW signal.

2. **Why the other choices are incorrect:**
   - **Choice B: A CW signal at a nearly pure audio frequency**
     - This choice is incorrect because a CW signal is typically at a radio frequency, not an audio frequency. The interference does not convert the RF signal into a pure audio tone.
   - **Choice C: A chirpy CW signal**
     - A "chirpy" CW signal refers to a CW transmission with frequency instability, often due to poor transmitter design or conditions. This is not the typical sound heard from RF interference in audio devices.
   - **Choice D: Severely distorted audio**
     - While RF interference can cause audio distortion, the specific interference from a CW transmitter is more likely to produce a distinct on-off pattern rather than general distortion.

In summary, the on-and-off nature of a CW signal is directly responsible for the humming or clicking sound heard in an audio device experiencing RF interference. This pattern is unique to CW transmissions and distinguishes it from other types of interference.