ARRL Technician Practice Exam

Which of the following is a likely cause of irregular fading of signals received by ionospheric reflection?

1. Weather conditions

2. Random combining of signals arriving via different paths

3. Static charge build-up

4. High altitude propagation

The correct answer is: Random combining of signals arriving via different paths

Irregular fading of signals received by ionospheric reflection is primarily caused by the random combining of signals that arrive via different paths. This phenomenon is known as multipath propagation. When radio waves are transmitted, they can reflect off the ionosphere and other structures, resulting in multiple copies of the same signal arriving at the receiving antenna at slightly different times and phases. Depending on these arrival times and phases, the signals can constructively or destructively interfere with each other, leading to fluctuations in the strength of the received signal, which is perceived as fading. In contrast, while weather conditions can affect the propagation and clarity of radio signals, they do not specifically cause the type of irregular fading associated with ionospheric reflection. Static charge build-up is not a typical factor influencing signal fading in this context, and although high altitude propagation can enhance signal reach, it is not related to the irregular fading seen with signals reflected from the ionosphere. Understanding these concepts is crucial for interpreting and managing communications that rely on ionospheric propagation, especially in variable conditions.