ARRL Technician Practice Exam

When is generally the best time for long-distance 10 meter band propagation via the F layer?

1. Nighttime during winter months

2. From dawn to shortly after sunset during high sunspot activity

3. During heavy rain or storms

4. Midday in summer

The correct answer is: From dawn to shortly after sunset during high sunspot activity

The best time for long-distance 10 meter band propagation via the F layer is generally from dawn to shortly after sunset during periods of high sunspot activity. This is due to the solar radio emissions and the resulting ionization of the F layer, which enhances propagation conditions. During high sunspot activity, the intensity of UV and X-ray radiation from the sun increases, which significantly ionizes the upper atmosphere, particularly the F layer. This ionization creates more reflective properties for radio waves, enabling them to travel greater distances. The phenomenon is most pronounced during the hours around dawn and shortly after sunset, as this is when the ionospheric conditions are optimal for reflecting HF signals. Other times, such as nighttime during winter months or during heavy rainfall, tend to see less favorable conditions for this type of propagation due to decreased ionization and other atmospheric factors. Midday in summer may result in some propagation, but it is typically not as effective as the dawn-to-sunset window during high sunspot activity. Understanding these factors can greatly assist in planning effective communication over long distances on the 10 meter band.