What is a likely cause of irregular fading of signals propagated by the ionosphere?
Frequency shift due to Faraday rotation
Interference from thunderstorms
Intermodulation distortion
Random combining of signals arriving via different paths✓الإجابة الصحيحة
الشرح
A signal returning from the ionized upper atmosphere usually arrives over several paths at once, differing in the number of hops and the height of reflection. Those copies drift in and out of phase as that region changes, and their random combination produces the irregular fading that is heard.