  The interest in the use of the HF band in telecommunication has increased
significantly in the last decade, mainly due to the development of new
standards for military telecommunications in HF, as well as the expansion of
digital broadcasting in the HF band. More specifically, these new standards
allow the implementation of links of hundreds or thousands of kilometers at a
low cost, which suggests a widespread adoption can occur. In Brazil, this type
of communication can be used in remote regions or regions of difficult access,
such as the Amazon rain-forest region. In addition to the evolution of
technologies concerning the physical layer of the HF telecommunication systems,
there has been a great development of techniques that use machine learning
algorithms for audio and image coding. It is believed that all these advances
will enable the use of the HF band for communication services in places without
telecommunication infrastructure. This work presents recent applications of HF
radio for digital links in Brazil, describing the challenges present for the
development of telecommunication systems in the HF band.
