Structure of signal received by passive ionospheric sounding in the HF band at the location of Timisoara, Romania

The ionospheric channel is time-variant and is affected by several factors such as variable attenuation, fading, modification of the polarization plane of waves, Doppler shift and nonlinearities. Therefore, communication channels through the ionosphere are subject to a high degree of variability. Nevertheless, communication through the ionospheric channel presents interest due to the modest requirements for infrastructure. In this paper, we report records of signals that are received by antennas in the HF band in Timisoara, Romania and we investigate the structure of these signals. This study is motivated by the future deployment of HF communication links for emergency situations.