What happens to HF propagation when the LUF exceeds the MUF?
The correct answer is A: Propagation via ordinary skywave communications is not possible over that path. What happens to HF propagation when the LUF exceeds the MUF is that propagation via ordinary skywave communications is not possible over that path. If LUF is higher than MUF, there's no usable frequency range - all frequencies are either too low (below LUF, too much absorption) or too high (above MUF, pass through). For amateur radio operators, this means the path is closed. Understanding this helps explain when paths are unusable.
Exam Tip
LUF exceeds MUF = propagation not possible. Think 'L'UF > 'M'UF = 'L'owest > 'M'aximum = 'N'o usable frequency. If LUF exceeds MUF, there's no frequency range that works - path is closed. Not enhanced, not double-hop, not all frequencies - just no propagation possible.
Memory Aid
"LUF exceeds MUF = propagation not possible. Think 'L'UF > 'M'UF = 'N'o usable frequency. If LUF exceeds MUF, there's no frequency range that works - path is closed. Propagation via ordinary skywave is not possible."
Real-World Application
LUF for a path is 15 MHz, and MUF is 12 MHz. Since LUF (15 MHz) exceeds MUF (12 MHz), there's no usable frequency - frequencies below 15 MHz are too low (below LUF, too much absorption), and frequencies above 12 MHz are too high (above MUF, pass through). The path is closed - no skywave propagation is possible.
Key Concepts
Why Other Options Are Wrong
Option B: Incorrect. HF communications aren't enhanced when LUF exceeds MUF - the path is closed, not enhanced. No frequencies work.
Option C: Incorrect. Double-hop propagation isn't more common - the path is closed, so no propagation occurs. Multiple hops don't help if LUF > MUF.
Option D: Incorrect. Propagation on all HF frequencies isn't enhanced - the path is closed. No frequencies work when LUF exceeds MUF.
题目解析
The correct answer is A: Propagation via ordinary skywave communications is not possible over that path. What happens to HF propagation when the LUF exceeds the MUF is that propagation via ordinary skywave communications is not possible over that path. If LUF is higher than MUF, there's no usable frequency range - all frequencies are either too low (below LUF, too much absorption) or too high (above MUF, pass through). For amateur radio operators, this means the path is closed. Understanding this helps explain when paths are unusable.
考试技巧
LUF exceeds MUF = propagation not possible. Think 'L'UF > 'M'UF = 'L'owest > 'M'aximum = 'N'o usable frequency. If LUF exceeds MUF, there's no frequency range that works - path is closed. Not enhanced, not double-hop, not all frequencies - just no propagation possible.
记忆口诀
LUF exceeds MUF = propagation not possible. Think 'L'UF > 'M'UF = 'N'o usable frequency. If LUF exceeds MUF, there's no frequency range that works - path is closed. Propagation via ordinary skywave is not possible.
实际应用示例
LUF for a path is 15 MHz, and MUF is 12 MHz. Since LUF (15 MHz) exceeds MUF (12 MHz), there's no usable frequency - frequencies below 15 MHz are too low (below LUF, too much absorption), and frequencies above 12 MHz are too high (above MUF, pass through). The path is closed - no skywave propagation is possible.
错误选项分析
Option B: Incorrect. HF communications aren't enhanced when LUF exceeds MUF - the path is closed, not enhanced. No frequencies work. Option C: Incorrect. Double-hop propagation isn't more common - the path is closed, so no propagation occurs. Multiple hops don't help if LUF > MUF. Option D: Incorrect. Propagation on all HF frequencies isn't enhanced - the path is closed. No frequencies work when LUF exceeds MUF.
知识点
LUF exceeds MUF, Path closure, No usable frequency, Propagation impossibility
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.