Editing Skywave (section)

===Low-angle skywaves===
[[File:PSKReporter Skip Example.jpg|thumb|Example of Skywave Propagation taken from [[PSK Reporter]].{{clarify|reason=What are "mins"?|date=February 2023}}|300x300px]]

The ionosphere is a region of the upper [[Earth's atmosphere|atmosphere]], from about 80&nbsp;km (50 miles) to 1000&nbsp;km (600 miles) in altitude, where neutral air is [[ion]]ized by solar [[photon]]s, [[solar particle event|solar particles]], and [[cosmic ray]]s. When [[high-frequency]] signals enter the ionosphere at a low angle they are bent back towards the Earth by the ionized layer.<ref>{{cite book |publisher=Sony Corporation |year=1998 |title=Wave Handbook |page=14 |oclc=734041509}}</ref> If the peak [[ionization]] is strong enough for the chosen frequency, a wave will exit the bottom of the layer earthwards – as if obliquely [[Reflection (physics)|reflected]] from a mirror. Earth's surface (ground or water) then [[Diffuse reflection|reflects]] the descending wave back up again towards the ionosphere.

When operating at frequencies just below the [[maximum usable frequency]], losses can be quite small, so the radio signal may effectively "bounce" or "skip" between the Earth and ionosphere two or more times (multi-hop propagation), even following the curvature of the Earth.  Consequently, even signals of only a few Watts can sometimes be received many thousands of miles away. This is what enables [[shortwave]] broadcasts to travel all over the world. If the ionization is not great enough, the wave only curves slightly downwards, and subsequently upwards as the ionization peak is passed so that it exits the top of the layer only slightly displaced. The wave is then lost in space. To prevent this, a lower frequency must be chosen. With a single "hop", path distances up to 3500&nbsp;km (2200 miles) may be reached. Longer transmissions can occur with two or more hops.<ref>{{cite book |author=Rawer, K. |title=Wave Propagation in the Ionosphere |publisher=Kluwer Academic Publications |location=Dordrecht |year=1993 |isbn=0-7923-0775-5}}</ref>