Ham Radio General Class Practice Test

Which ionospheric layer is most absorbent of long skip signals during daylight hours on frequencies below 10 MHz?

1. The F2 layer

2. The F1 layer

3. The E layer

4. The D layer

The correct answer is: The D layer

The D layer of the ionosphere is known for its significant absorbent properties, particularly during daylight hours. When the sun is shining, solar radiation ionizes this layer, which in turn increases its density and consequently its ability to absorb radio waves, particularly at frequencies below 10 MHz. As a result, long skip signals, which rely on reflection from the ionosphere, face considerable attenuation in this layer during daylight due to the absorption effects. In contrast, the F2 layer is primarily responsible for long-distance communication but operates more effectively during nighttime when it is less influenced by absorption. The E layer has a different role in ionospheric propagation and helps with certain types of propagation, primarily on higher frequencies. The F1 layer, similar to the F2 layer, isn’t as absorbent as the D layer during daylight hours. Thus, the D layer's unique characteristics make it the most absorbent layer for long skip signals in the specified conditions.