*Question G8C07:
Which of the following narrow-band digital modes can receive signals with very low signal-to-noise ratios?*  

*Correct Answer is  B: FT8*  

### AI Response: (may contain errors)  

FT8 is the correct answer because it is specifically designed to decode signals with very low signal-to-noise ratios (SNR). Here's why:

1. **Why FT8 is Correct:**
   - FT8 is a digital mode that uses very narrow bandwidth and sophisticated error-correcting algorithms, allowing it to decode signals with SNRs as low as -20 dB. This makes it highly effective for weak signal communication.

2. **Why the Other Choices are Incorrect:**
   - **MSK144**: This mode is used primarily for meteor scatter communication. It is not optimized for low SNR conditions like FT8.
   - **AMTOR**: An older digital mode used for teletype communication. It requires a better SNR compared to FT8 and is not as effective in weak signal conditions.
   - **MFSK32**: A multi-frequency shift keying mode that is more robust than some other modes but still not as effective as FT8 in very low SNR environments.

3. **Useful Information:**
   - FT8 uses an 8-tone frequency shift keying (FSK) modulation and transmits in 15-second intervals, which contributes to its ability to work with weak signals.
   - The narrow bandwidth and time synchronization of FT8 help in achieving successful decodes even when signals are barely above the noise floor.

Understanding these characteristics of FT8 and the limitations of other modes will help you recognize why FT8 is the best choice for low SNR conditions.