*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 levels used to modulate the signal are too high, leading to distortion and loss of signal integrity. 

### Correct Answer: D - Excessive transmit audio levels

- **Explanation**: 
  - When the audio levels are too high, the modulation can exceed the linear range of the transmitter. This results in distortion, where the peaks of the audio waveform are clipped, causing overmodulation. This can lead to a signal that is difficult to decode and can interfere with adjacent channels.

### Why the Other Choices are Incorrect:

- **A: Excessive numbers of retries**: 
  - This refers to the number of times a transmission is attempted due to errors. While it can indicate problems with the signal, it does not directly cause overmodulation.

- **B: Excessive frequency deviation**: 
  - Frequency deviation is the amount by which the frequency of the transmitted signal varies from the carrier frequency. While excessive deviation can affect signal quality, it is not the primary cause of overmodulation in AFSK. Overmodulation is more directly related to audio levels.

- **C: Bit errors in the modem**: 
  - Bit errors occur during the transmission and reception of data, often due to noise or interference. While they can affect the integrity of the received signal, they do not cause overmodulation. Overmodulation is specifically related to the modulation process itself, not the errors in data transmission.

### Summary:
To avoid overmodulation in AFSK signals, ensure that the transmit audio levels are kept within an appropriate range, typically around 50-75% of the maximum level to maintain linearity and prevent distortion.