6. Applications in high-frequency listening and radio communications

6.1 Experimental context

The high-frequency (HF) range (3 to 30 MHz) is widely used, particularly for long-distance military radiocommunications, exploiting the reflection of these waves on the various layers of the ionosphere. The high level of spectral congestion in this frequency range, combined with the presence of propagation multipaths at reception, induced by the reflection of waves on the various layers of the ionosphere, means that source separation techniques, or even propagation multipaths, need to be implemented at the receiver, for both radiocommunications and passive listening applications. In the latter case, this separation must be carried out without any a priori information on the sources received, i.e. in a purely self-taught manner.

It was...