A system for measuring the characteristics of the ionospheric channel by digital transmissions

The increase of digital transmission rates in the decametric range, by adaptative modems was examined. The ionospheric channel is defined for its rapid fluctuations, and its slower time evolutions. The measuring system is designed to provide for two types of ionospheric medium studies. The first study estimates the main parameters of the channel transfer function, with an update process in the order of 10 milliseconds. With such a cyclic-rate analysis, constraints of data recording restrict the length of the observations. The system gives information about the channel time-variation characteristics over intervals of a few tens of seconds, and thus allows a survey of the average behavior of the channel in a quasi-continuous manner. The first results obtained during an experiment at vertical incidence to validate equipment and measurement technique are presented.