Anomalies in NAVTEX Signal Reception in the Northern Adriatic: Discrepancies between Measurements and Propagation Models

This research analyzes in detail the reception of NAVTEX signals in the northern Adriatic, revealing significant discrepancies between empirical observations and predictions of standard groundwave propagation models. The NAVTEX receiver at a fixed location on shore consistently failed to receive NAVTEX messages during daytime broadcasts from the Split and Piombino stations, despite being within their coverage area. At the same time, signals and messages from the nearest Mondolfo station were reliably received. Signal strength measurements confirmed that the signals from Split and Piombino stations were weak and unstable, while Mondolfo station provided a strong and stable signal. Comparison of these observations with the predictions of propagation models showed that the models predict signal strengths which should be sufficient for detection from all stations, including Split and Piombino. These findings indicate that current propagation models fail to accurately capture complex environmental factors or potential transmitter performance issues. It is concluded that these models cannot be reliably used to predict NAVTEX coverage in such complex maritime environments, which has critical implications for maritime safety due to the inability to receive Maritime Safety Information (MSI) via the NAVTEX system.