What is a likely cause of irregular fading of signals propagated by the ionosphere?

• A. Random combining of signals arriving via different paths
• B. Constant signal strength from a single path
• C. Amplification of signals by the atmosphere
• D. Predetermined signal loss rates based on distance

Answer: (A)

Irregular fading of signals propagated by the ionosphere is primarily caused by the random combining of signals arriving via different paths. This phenomenon occurs when radio waves travel from a transmitter to a receiver via various routes, often due to reflections from the ionosphere. Each of these paths can have different lengths and conditions, which leads to variations in signal phase and amplitude when they reach the receiver.

When the signals from these multiple paths arrive together, they can constructively or destructively interfere with each other. Constructive interference occurs when the signals are in phase, leading to a stronger combined signal, while destructive interference occurs when the signals are out of phase, causing signal reduction or fading. This results in the irregular fading characteristic of ionospheric propagation, where the signal strength can fluctuate unpredictably.

The other options do not accurately describe the cause of this irregular fading. A constant signal strength from a single path would not result in fading, as there would be no variability in the signal received. Amplification of signals by the atmosphere would generally lead to increased signal strength rather than irregular fading. Lastly, predetermined signal loss rates based on distance are not representative of the dynamic nature of ionospheric propagation and the randomness involved in multi-path reception. Thus, the randomness of combining