Ham Amateur Radio Technician Practice Exam

What effect does the D region have on signals during daytime on the lower HF bands?

1. It strengthens them

2. It has no impact

3. It absorbs signals

4. It reflects them back

The correct answer is: It absorbs signals

The D region of the ionosphere plays a significant role in the propagation of radio signals, particularly within the lower HF bands, during the daytime. During daylight hours, this region becomes highly ionized due to the sun's ultraviolet radiation, which leads to increased absorption of radio waves in the lower frequency range. As a result, signals in the lower HF bands encounter greater attenuation or absorption when they pass through the D region. This absorption can lead to a substantial reduction in signal strength, making it more difficult for lower HF band communications to occur effectively. This phenomenon is particularly evident in frequencies below about 10 MHz where the D region's effects are most pronounced. Understanding this absorption is crucial for amateur radio operators to adapt their communication strategies, especially during the day when using lower HF frequencies.