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

Choices:  
A: It varies with the amount of data  
B: 8 seconds  
C: 15 seconds  
D: 30 seconds    

Correct Answer is  C: 15 seconds  

For FT8, transmissions occur in synchronized 15-second time slots. Each station transmits during one slot and listens during the next.

Why C (15 seconds) is correct:
- FT8 uses fixed, UTC-synchronized 15-second slots. One “transmission cycle” is one slot.
- Within each 15-second slot, the RF is on for about 12.6 seconds, leaving time for decoding and turnaround.

Helpful timing relationships:
- Slot length: $$T_{\text{slot}} = 15\ \text{s}$$
- Approximate RF-on time: $$T_{\text{RF}} \approx 12.6\ \text{s}$$
- Round-trip (one TX slot + one RX slot): $$T_{\text{round-trip}} \approx 2T_{\text{slot}} = 30\ \text{s}$$

Why the other choices are incorrect:
- A: It varies with the amount of data — Incorrect. FT8 uses fixed-length frames and FEC; timing is fixed, not variable.
- B: 8 seconds — Incorrect. That’s a distractor near FT4 timing (about 7.5 s), not FT8.
- D: 30 seconds — Incorrect for a single transmission cycle. 30 seconds is two slots (a full TX+RX exchange), not one FT8 transmission slot.