Radio frequency (RF) transmissions between 3 and 30 MHz are designated in the Radio Regulations as High Frequency (HF) bands or “band 7”, corresponding to “Decametric waves” in the metric subdivision. Similarly, symbol “MF” applies to 300-3 000 kHz (band 6) or “Hectometric waves”. MF/HF communications have been widely used for nearly 80 years to provide communications to long distances and remote areas via the ionosphere. Although of lower reliability and limited bandwidth with respect to other radiocommunication systems operating in higher frequency bands, MF/HF systems allow very inexpensive telecommunication radio links over long distances and much quicker establishment than other terrestrial or satellite systems, notably in the case of natural disasters or man-made conflicts. Evolution of technologies during the last decades, such as adaptive systems, has provided the opportunity for a renewal of interest for these applications.