(2025-07-20) PE1ITR

Introduction

Following the previous analysis of tropospheric propagation (“tropo”) over the Alps, this article focuses on airplane scatter as the primary propagation mode for VHF DXpeditions in the Alpine region.
While tropo openings on 144 MHz can provide exceptional conditions, they are rare—occurring only a few days per year—and prove even less useful at 432 MHz due to higher coupling losses between inversion layers. In contrast, airplane scatter offers a more consistent opportunity for long-distance contacts, making it an attractive and predictable option for portable operations.

Air Traffic Patterns over the Alps

To assess the potential for airplane scatter, I analyzed air traffic data collected via ADS-B receivers from the airscatter HAM radio network. This dataset provided insight into the major flight routes crossing the Alps on three separate days—Friday, Saturday, and Sunday which correspond to the days I plan to be portable in the region.
The resulting plots show that, although there are minor day-to-day variations, the main flight corridors remain broadly similar on all three days. While it is possible that other times of day might offer even better opportunities for scatter, my analysis focused on the afternoon hours, matching my planned periods of activity. These flight patterns form a stable basis for predicting airplane scatter opportunities during portable operations.

Figure 1


Airplane density heatmap of main flight corridors over the Alps on July 18, 2025, based on ADS-B data. Only flights above 10 km altitude are included. Each color spot represents the number of aircraft passing through a 3 x 3 km grid cell; only cells with more than 5 aircraft positions are shown. The heatmap reveals the primary air traffic routes, which are critical for planning VHF airplane scatter contacts across the Alpine region.

Figure 2



Figure 3



Target DX Locations, Optimizing Scatter Locations and Timing

The next step was to identify potential DX partners on the southern side of the Alps. I selected ten well-known Italian stations located in the regions of Milan, Parma, Modena, Bologna, Venice, and Trieste. Basicly stations from the JN34, JN44, JN45, JN54 en JN65 grid square. I have previously worked some of these stations from Luxembourg (JO30) via airplane scatter. Mostly on 144 MHz and occasionally even on 432 MHz, with successful contacts up to 730 km. These locations serve as practical and proven targets for scatter analysis.

To maximize the chances of successful contacts, I analyzed each possible grid square on the northern side of the Alps. For each, I calculated which sub-square would offer the greatest number of aircraft in the scatter midpoint (10 x 40 km) during each hour of the afternoon (13–19 UTC), for all target stations. The top three sub-squares per grid square were identified, ranked by the number of flights in the scatter area for all targets combined. For each, I also determined the optimal hour with the highest aircraft density, thereby defining the most promising window for activity.

Verification and Practical Planning

For the best sub-square in each grid, I plotted the hourly distribution of aircraft in the scatter midpoint for each of the ten Italian stations. These plots, with time on the x-axis and the number of aircraft on the y-axis, help verify whether the predicted peak aligns with a practical operating window, and also allow me to determine realistic start and stop times for activity. In reality, the “best” scatter sub-square may not always be easily accessible or ideal as a take-off location. Therefore, in the final planning, I also considered nearby sub-squares, balancing theoretical optimality with practical considerations on-site.

Conclusion

This analysis demonstrates that, due to its reliability and predictability, airplane scatter is the key propagation mode for VHF DX over the Alps. Especially compared to the much rarer tropo conditions, and even more so at higher frequencies. By combining air traffic data with scatter geometry, it is possible to plan portable operations with a high probability of success, targeting specific time windows and locations to maximize the number of workable Italian DX stations.




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