Which of the following is typical of the lower HF frequencies during the summer?
Poor propagation at any time of day
World-wide propagation during daylight hours
Heavy distortion on signals due to photon absorption
High levels of atmospheric noise or static✓Правильный ответ
Объяснение
Summer brings widespread thunderstorm activity, and lightning is a broadband impulsive source whose energy is strongest at low frequencies and propagates efficiently by skywave at MF and low HF. The result on 160, 80 and 40 meters is a high static level rather than any change to the propagation mechanism itself.