A transmitted radio signal reaches a receiver by both one-hop and two-hop skip paths. What can small changes in the ionosphere cause?

When a radio signal reaches a receiver via multiple paths, such as a combination of one-hop and two-hop skips, the phenomenon is called multipath propagation. Because these paths are of different lengths, the distinct wave fronts arrive at the receiving antenna at slightly different times and phases. The ionosphere is a dynamic medium that constantly ripples and shifts. Even small variations in its structure will minutely alter the distance the radio waves must travel, causing the arriving waves to continuously shift in and out of phase with one another. When the waves arrive in phase, they combine to make the signal stronger (constructive interference). When they arrive out of phase, they cancel each other out (destructive interference). This rapid, continuous fluctuation results in noticeable variations in signal strength, commonly known as multipath fading.