*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 consider the bandwidth requirements of each option.

1. **Correct Answer: FT8**
   - FT8 is designed for weak signal communication and operates with a bandwidth of approximately 50 Hz. This narrow bandwidth allows it to be effective in crowded band conditions, making it suitable for low-power operations.

2. **Why the other choices are incorrect:**
   - **A: MFSK16**
     - MFSK16 typically has a bandwidth of about 200 Hz. While it is efficient, it is wider than FT8.
   - **B: 170 Hz shift, 45-baud RTTY**
     - RTTY (Radio Teletype) with a 170 Hz shift and 45 baud rate has a bandwidth of approximately 170 Hz. This is wider than FT8.
   - **D: PACTOR IV**
     - PACTOR IV can have a bandwidth of around 200-300 Hz, depending on the specific settings and conditions. This is significantly wider than FT8.

3. **Useful Rules of Thumb:**
   - Digital modes generally have bandwidths that can be estimated based on their modulation techniques and baud rates. A common rule of thumb is that the bandwidth is roughly equal to the baud rate multiplied by a factor (often around 1.2 to 2).
   - For example, for RTTY, the bandwidth can be approximated as:
     $$ \text{Bandwidth} \approx \text{Shift} + \text{Baud Rate} $$

In summary, FT8 has the narrowest bandwidth of the options provided, making it the correct answer for this question.