*Question T8A10:
What is the approximate bandwidth of AM fast-scan TV transmissions?*  

*Correct Answer is  B: About 6 MHz*  

### AI Response: (may contain errors)  

The correct answer to the question about the approximate bandwidth of AM fast-scan TV transmissions is **B: About 6 MHz**. 

### Explanation of the Correct Answer:
- **AM Fast-Scan TV Bandwidth**: 
  - Fast-scan television (TV) using amplitude modulation (AM) typically requires a bandwidth of about 6 MHz. This is because AM video signals need to transmit a significant amount of information, including both the luminance (brightness) and chrominance (color) components of the video signal.
  
### Why the Other Choices are Incorrect:
- **A: More than 10 MHz**: 
  - This choice is incorrect because while some high-definition video formats may require more bandwidth, standard AM fast-scan TV does not exceed 6 MHz.
  
- **C: About 3 MHz**: 
  - This is also incorrect as it underestimates the bandwidth needed for AM fast-scan TV. A bandwidth of 3 MHz would not be sufficient to carry the full video signal quality required for fast-scan TV.
  
- **D: About 1 MHz**: 
  - This choice is incorrect as it significantly underestimates the bandwidth. A bandwidth of 1 MHz is too narrow for AM fast-scan TV, which would result in poor video quality.

### Useful Rules of Thumb:
- For standard AM fast-scan TV, the bandwidth is typically around 6 MHz.
- In general, the bandwidth for video signals can be estimated using the formula:
  
$$
BW \approx 2 \times f_{max}
$$

where $f_{max}$ is the maximum frequency of the video signal. For AM fast-scan TV, this results in a bandwidth of about 6 MHz, which is consistent with the requirements for transmitting a full video signal. 

This understanding is crucial for the Extra Class exam, as it helps in grasping the technical requirements for various modes of transmission.