Kennelly–Heaviside layer

The Kennelly-Heaviside layer was named after scientists Arthur Edwin Kennelly and Oliver Heaviside. Its existence was shown in 1924 by Edward V. Appleton, an English physicist who received the Nobel Prize in the year 1947. The Kennelly-Heaviside layer or E region is part of the ionosphere, the top part of the Earth's atmosphere which is full of electricity and magnetism, 90 to 150 kilometers from the Earth's surface. The layer is capable of reflecting medium shortwave electromagnetic radiations, or the EM radiations whose frequency ranges between 300 kHz to 3MHz. 
This layer became a popular means of communication in the late 1920's when AM signals (Amplitude Modulated) were transmitted over long distances. AM signals can bounce off the Kennelly-Heaviside. They can go further than signals which cannot bounce off the layer. This means that the sender and receiver of the signal could be over the horizon from each other, and the signal can bounce off the layer in the sky in between them.