*Question E2D09:
What type of modulation is used by JT65?*  

*Correct Answer is  A: Multitone AFSK*  

### AI Response: (may contain errors)  

JT65 is a digital mode used in amateur radio that employs a specific type of modulation known as Multitone AFSK (Audio Frequency Shift Keying). 

### Explanation of the Correct Answer:
- **Multitone AFSK**: 
  - JT65 uses multiple tones to represent different bits of information. It transmits data in 65-second intervals, allowing for weak signal communication. The modulation scheme allows for robust error correction, making it effective for low signal-to-noise ratios.

### Why the Other Choices are Incorrect:
- **A: Multitone AFSK**: This is the correct answer, as explained above.
  
- **B: PSK (Phase Shift Keying)**: 
  - PSK modulates the phase of a carrier wave to represent data. While it is a popular digital mode, JT65 does not use this method; instead, it relies on multiple tones.

- **C: RTTY (Radio Teletype)**: 
  - RTTY is a form of frequency shift keying (FSK) that uses two frequencies to represent binary data. JT65 is not RTTY, as it employs a more complex multitone approach.

- **D: QAM (Quadrature Amplitude Modulation)**: 
  - QAM combines both amplitude and phase modulation to transmit data. JT65 does not utilize this method; it specifically uses multitone AFSK.

### Summary:
- JT65 is characterized by its use of **Multitone AFSK**, which allows for effective communication under challenging conditions. Understanding the differences between these modulation types is crucial for the Extra Class exam.