*Question E2E10:
Which of these digital modes has the narrowest bandwidth?*  

*Correct Answer is  C: FT8*  

### AI Response: (may contain errors)  

To determine which digital mode has the narrowest bandwidth, we need to understand the typical bandwidths associated with each mode:

1. **FT8**:  
   - FT8 is a digital mode designed for weak signal communication. It uses a very narrow bandwidth of approximately 50 Hz. This makes it the narrowest among the options provided.

2. **MFSK16**:  
   - MFSK16 is a multi-frequency shift keying mode that typically uses a bandwidth of about 316 Hz. This is wider than FT8.

3. **170 Hz shift, 45-baud RTTY**:  
   - RTTY (Radio Teletype) with a 170 Hz shift and 45 baud rate has a bandwidth of approximately 300 Hz. This is also wider than FT8.

4. **PACTOR IV**:  
   - PACTOR IV is a mode used for robust data transmission, and it can have a bandwidth of up to 2400 Hz, depending on the configuration. This is significantly wider than FT8.

### Summary:
- **Correct Answer: FT8**  
  FT8 has the narrowest bandwidth at approximately 50 Hz, making it ideal for weak signal conditions.

- **Incorrect Choices**:  
  - **MFSK16**: 316 Hz bandwidth, wider than FT8.  
  - **170 Hz shift, 45-baud RTTY**: 300 Hz bandwidth, wider than FT8.  
  - **PACTOR IV**: Up to 2400 Hz bandwidth, much wider than FT8.

Understanding these bandwidths helps in selecting the appropriate mode for specific communication needs, especially in crowded or weak signal environments.