Editing Skywave (section)

===Fading===

At any distance sky waves will fade. The layer of ionospheric [[Plasma (physics)|plasma]] with sufficient ionization (the reflective surface) is not fixed, but undulates like the surface of the ocean.  Varying reflection efficiency from this changing surface can cause the reflected signal strength to change, causing "''[[fading]]''" in shortwave broadcasts.  Even more serious [[selective fading|fading]] can occur when signals arrive via two or more paths, for example when both single-hop and double-hop waves interfere with other, or when a skywave signal and a ground-wave signal arrive at about the same strength. This is the most common source of fading with nighttime AM broadcast signals.
Fading is always present with sky wave signals, and except for digital signals such as [[Digital Radio Mondiale]] seriously limit the fidelity of shortwave broadcasts.