Radio Communications, Ionospheric

radio communications by means of the reflection of decameter radio waves (at frequencies of 3–30 megahertz) from the ionized layers of the atmosphere.

Ionospheric radio communications are characterized by a great range and low rate of message transmission, variability of the medium by which the radio waves are propagated (because of the close relation between the properties of the ionosphere and solar activity), attenuation and distortion of signals (because of fluctuations in the dialectric permeability of the medium), and multiray propagation. Adaptive systems with automatic error challenge (in telegraphy) and controlled companding of transmitted signals (in telephony) are used for stable ionospheric radio communications with minimal signal distortion. Multiplexing systems for single-side-band radio channels are used to increase the carrying capacity. The development of digital radio channels makes it possible to use ionospheric radio communications to transmit telephonic, telegraphic, and phototelegraphic signals and data in binary form. Despite the development of multichannel ground communications and the use of communications satellites, ionospheric radio communications remains profitable and is sometimes the only type of low-channel communications used for great distances; for example, it is used to transmit reports of natural disasters to remote mobile objects.