*Question E8D08:
What parameter evaluates distortion of an AFSK signal caused by excessive input audio levels?*  

*Correct Answer is  D: Intermodulation Distortion (IMD)*  

### AI Response: (may contain errors)  

To evaluate distortion of an AFSK (Audio Frequency-Shift Keying) signal caused by excessive input audio levels, we look at **Intermodulation Distortion (IMD)**.

### Explanation:

1. **Correct Answer: D - Intermodulation Distortion (IMD)**
   - **IMD** occurs when multiple signals mix together in a non-linear device, such as an overdriven amplifier. This mixing creates additional, unwanted frequencies that can distort the original signal. In the context of AFSK, excessive audio input levels can cause the transmitter to operate non-linearly, leading to IMD and thus distorting the signal.

2. **Why the Other Choices are Incorrect:**
   - **A: Signal-to-noise ratio**
     - This measures the level of the desired signal compared to the background noise. It does not specifically address distortion caused by excessive input levels.
   - **B: Baud error rate**
     - This refers to errors in the transmission rate of data, not directly related to audio distortion.
   - **C: Repeat Request Rate (RRR)**
     - This is a measure of how often data packets need to be retransmitted due to errors, which is not a direct measure of audio distortion.

### Useful Concepts:

- **Non-linear Distortion:** When a system is overdriven, it does not respond linearly to input signals, leading to distortion products like IMD.
- **AFSK Signal:** A type of frequency modulation where digital data is represented by changes in the frequency of an audio tone.

Understanding IMD is crucial for ensuring clean and clear signal transmission, especially in digital modes like AFSK.