*Question E8D07:
What is a common cause of overmodulation of AFSK signals?*  

*Correct Answer is  D: Excessive transmit audio levels*  

### AI Response: (may contain errors)  

Overmodulation of AFSK (Audio Frequency Shift Keying) signals occurs when the audio input to the transmitter is too high, causing distortion and interference. Let's break down the choices:

1. **Correct Answer: D: Excessive transmit audio levels**
   - **Explanation**: Overmodulation happens when the audio signal driving the transmitter is too strong. This causes the signal to exceed the linear range of the transmitter, leading to distortion and splatter. In AFSK, where audio tones are used to modulate the carrier, keeping the audio levels within the proper range is crucial to avoid overmodulation.

2. **Why the other choices are incorrect:**
   - **A: Excessive numbers of retries**
     - Retries are related to data transmission protocols and do not directly affect modulation levels. They occur when data packets are not acknowledged, often due to poor signal conditions, but they do not cause overmodulation.
   - **B: Excessive frequency deviation**
     - Frequency deviation refers to the extent of frequency change in FM signals. While excessive deviation can cause issues in FM, AFSK uses audio tones to modulate the carrier, and overmodulation is more about audio levels than frequency deviation.
   - **C: Bit errors in the modem**
     - Bit errors are a result of poor signal quality or interference but do not cause overmodulation. They are a symptom rather than a cause of modulation issues.

**Rule of Thumb**:  
To prevent overmodulation, ensure that the audio input level to the transmitter is set correctly. Use a modulation meter or follow the manufacturer's guidelines to adjust audio levels appropriately.