HF transmission of numerical data

In the field of digital transmissions, the major characteristic of the ionosphere is that it behaves as a multipath propagation medium. This paper describes a type of 1,200 bits/s - MODEM fitted to that kind of transmission medium and which is to be used for SSB radio transmission. After a short introduction about data transmission on HF channels, the MODEM operation mode and its implementation are reviewed; to conclude, the MODEM real life experiment results are discussed.