*Question G8A09:
What type of modulation is used by FT8?*  

*Correct Answer is  A: 8-tone frequency shift keying*  

### AI Response: (may contain errors)  

FT8 is a digital mode used in amateur radio that employs a specific type of modulation known as 8-tone frequency shift keying (8FSK). 

### Explanation of the Correct Answer:
- **Correct Answer: A: 8-tone frequency shift keying**
  - FT8 uses 8FSK, which means it transmits data by shifting between 8 different frequencies. Each frequency represents a different symbol, allowing for efficient data transmission even in low signal conditions. This modulation technique is particularly effective for weak signal communication.

### Explanation of Incorrect Answers:
- **B: Vestigial sideband**
  - Vestigial sideband (VSB) is a form of amplitude modulation that is used primarily in television broadcasting. It is not a digital mode and does not apply to FT8.

- **C: Amplitude compressed AM**
  - Amplitude compressed AM refers to a method of amplitude modulation that reduces the dynamic range of the signal. FT8 does not use amplitude modulation; it relies on frequency shifts instead.

- **D: 8-bit direct sequence spread spectrum**
  - Direct sequence spread spectrum (DSSS) is a technique used in some digital communications to spread the signal over a wider bandwidth. FT8 does not use this method; it specifically uses frequency shift keying.

### Summary:
FT8's use of 8-tone frequency shift keying allows it to effectively transmit data in challenging conditions, making it a popular choice among amateur radio operators for digital communication. Understanding the modulation types helps in grasping how different digital modes operate and their applications in amateur radio.