GeneralG3B11
What happens to HF propagation when the LUF exceeds the MUF?
A
Answer
Radio wave propagation
Type
A
Propagation via ordinary skywave communications is not possible over that path
B
HF communications over the path are enhanced
C
Double-hop propagation along the path is more common
D
Propagation over the path on all HF frequencies is enhanced
Answer Notes
The MUF (Maximum Usable Frequency) is the highest frequency that will bounce off the ionosphere for a given path. The LUF (Lowest Usable Frequency) is the lowest frequency that will not be completely absorbed by the D region of the ionosphere.
For skywave communication to happen, you must pick a frequency between the LUF and the MUF. If the LUF rises higher than the MUF, the "window" of usable frequencies closes completely.
Therefore, no ordinary skywave propagation is possible over that specific path. Any frequency high enough to escape D-layer absorption will be too high to be refracted by the F-layer, and vice versa.
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What is the approximate maximum distance along the Earth’s surface normally covered in one hop using the E region?
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Which of the following is typical of the lower HF frequencies during the summer?