The ionosphere plays an important role in the wave propagation of
radio waves. It is an area of ions located between the stratosphere and the exosphere at an altitude of about 50 km to 400 km above the earth's surface. The ionosphere is not homogeneous and can transmit, diffract, reflect, absorb or scatter radio waves depending on their frequencies. As solar radiation increases, it absorbs radio waves more. This means that the absorption is stronger during the day than at night. Space waves
are reflected at the ionosphere. Theionosphere is divided into several height regions, which are marked with letters. The lowest region between about 50 km and 100 km is the D-region, above that up to about 150 km is the E-region. In the E-region sporadic strongly ionizing regions occur in the summer months, in which short waves
but also ultra-short waves are reflected. These regions are called Sporadic-E (Es)F region has a higher density of free electrons caused by increased ionization from solar radiation. The F region reflects frequencies up to about 10 MHz and partially absorbs higher frequencies. The F1 region
is only present during the day and cannot always be observed. It has an electron density of about 5x10exp5 free electrons per cubic centimeter, which can increase by a power of ten during strong sunlight and decrease by a power of ten at night. The F2 region is the actual reflection layer, it reflects RF frequencies equally during the day and at night.
It has about 10exp6 free electrons per cubic centimeter. Large fluctuations can occur in the F2 region, mainly caused by magnetic storms.