5. Summary and conclusions
The purpose of this work was to analyze the amplitude and phase data acquired by monitoring at Belgrade site VLF/LF radio signals emitted by four European transmitters during a seven-year period (2008–2014). The results of amplitude and phase variations on GQD/22.10 kHz, DHO/23.40 kHz, ICV/20.27 kHz and NSC/45.90 kHz radio signals measurements at short path over Central Europe and their interpretation are summarized here. The most important factors affecting those paths under uniform background conditions are the transmitter frequency, geographical location, the electron density profile, and the ground conductivities encountered.
Our attention is restricted to regular diurnal, seasonal and solar variations including sunrise and sunset effects on propagation characteristics of VLF/LF radio signals. All the paths are similarly illuminated during daytime condition and there are differences in the level of illumination during dawn and dusk in accordance to geographic coordinates of transmitters. We accepted the results obtained by Volland (1964) that VLF radio signals propagating from transmitter to receiver over paths with distance D