Ham Radio General Class Practice Test

What happens to HF propagation when the Lowest Usable Frequency (LUF) exceeds the Maximum Usable Frequency (MUF)?

1. No HF radio frequency will support ordinary skywave communications over the path

2. HF communications over the path are enhanced

3. Double hop propagation along the path is more common

4. Propagation over the path on all HF frequencies is enhanced

The correct answer is: No HF radio frequency will support ordinary skywave communications over the path

When the Lowest Usable Frequency (LUF) exceeds the Maximum Usable Frequency (MUF), it indicates that the frequencies suitable for propagation via the ionosphere are no longer viable for communication. The LUF represents the lowest frequency at which signals can be effectively transmitted and received, while the MUF is the highest frequency that can be propagated without loss. When LUF surpasses MUF, it signifies that even the lower frequencies are experiencing degradation due to ionospheric conditions. As a result, no effective skywave communications can occur for any frequency within the HF band over that specific propagation path. This effectively indicates a communication blackout for HF radio frequencies along that route. Such conditions might arise during certain solar or atmospheric events affecting the ionization of the layers responsible for HF propagation. Options that suggest enhanced or more common propagation contradict the fundamental principles of ionospheric propagation and how LUF and MUF interact. Thus, the correct understanding highlights the critical nature of the LUF and MUF relationship in determining usable frequencies for HF communications.