Deep Dive: T3C09
The correct answer is A: From dawn to shortly after sunset during periods of high sunspot activity. The best time for long-distance 10-meter band propagation via the F region is from dawn to shortly after sunset during periods of high sunspot activity. The F region of the ionosphere is most effective during daylight hours when solar radiation is strongest. The F region (specifically F2) is the highest and most effective ionospheric layer for long-distance HF propagation. It's most active during daylight hours when solar radiation ionizes the upper atmosphere. During high sunspot activity, the ionosphere is more intensely ionized, making F region propagation more reliable and extending to higher frequencies like 10 meters. Nighttime propagation on 10 meters is less reliable because the F region weakens after sunset.
Why Other Answers Are Wrong
Option B: Incorrect. Nighttime (after sunset to dawn) is not the best time for 10-meter F region propagation. The F region weakens at night. Option C: Incorrect. Low sunspot activity reduces F region effectiveness. High sunspot activity is needed for reliable 10-meter propagation. Option D: Incorrect. Nighttime with low sunspot activity is the worst combination. You need daylight and high sunspot activity.
Exam Tip
10m F region = Daytime, high sunspots. Remember: Best 10-meter F region propagation is from dawn to shortly after sunset during high sunspot activity. Daylight and high sunspots are both needed.
Memory Aid
**1**0m **F** region = **D**aylight **H**igh **S**unspots (think '10F = DHS' = Daylight High Sunspots)
Real-World Example
You're operating on 10 meters during a period of high sunspot activity. In the morning, the band starts to open as the sun rises and the F region becomes active. Throughout the day, you make excellent long-distance contacts via F region propagation. As sunset approaches, the F region weakens and 10-meter propagation becomes less reliable. The combination of daylight and high sunspot activity provides the best conditions.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T3C
Reference: FCC Part 97.3
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T3C topic.