*Question E2E06:
What is the length of an FT8 transmission cycle?*  

*Correct Answer is  C: 15 seconds*  

### AI Response: (may contain errors)  

FT8 is a digital mode used in amateur radio that is designed for weak signal communication. It is part of the WSJT-X software suite and is popular for its efficiency in making contacts under challenging conditions.

### Explanation:

1. **Correct Answer: 15 seconds (Choice C)**
   - FT8 operates on a fixed cycle of 15 seconds. Each transmission lasts for 15 seconds, followed by a 15-second listening period. This means that a complete cycle (transmit and receive) takes 30 seconds, but each individual transmission is 15 seconds long.

2. **Why Other Choices Are Incorrect:**
   - **Choice A: It varies with the amount of data**
     - This is incorrect because FT8 uses a fixed-length transmission cycle regardless of the amount of data being sent. The protocol is designed to send a standard message within the 15-second window.
   - **Choice B: 8 seconds**
     - This is incorrect because FT8 specifically uses a 15-second transmission period. An 8-second cycle is not part of the FT8 protocol.
   - **Choice D: 30 seconds**
     - This is incorrect for the length of a single transmission. While a full cycle (transmit and receive) is 30 seconds, each transmission itself is only 15 seconds.

### Key Points:
- FT8 uses a fixed 15-second transmission period.
- The protocol is designed for efficient communication with weak signals.
- Understanding the timing of FT8 is crucial for synchronizing transmissions and receptions effectively.