Question
What is a likely cause of irregular fading of signals propagated by the ionosphere?
Answer Options
- A) Frequency shift due to Faraday rotation
- B) Interference from thunderstorms
- C) Intermodulation distortion
- D) Random combining of signals arriving via different paths
Correct Answer: D
Explanation
HF signals travel long distances by bouncing off the ionosphere, a layer of charged particles in the Earth’s upper atmosphere. This bouncing process can cause the signal to arrive at the receiving station via multiple paths (multi-hop propagation), where a signal might bounce off the ionosphere one, two, or three times.
Because the ionosphere is constantly moving and changing, these multiple paths are constantly shifting. The result is the random combining of signals arriving via different paths at slightly different times, causing the slow, irregular fading in signal strength commonly known as QSB.
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