AVIONIX installed the ATC Frequency Monitoring System at Zagreb Airport to monitor and analyze data on the 1030 and 1090MHz surveillance frequencies. SAT was passed on 16th of November, 2018. The system consists of two redundant receiver stations, which both receive signals on 1030 and 1090 MHz frequencies by high sensitive SDR radios. The processing and archiving of data is perfomed by a central server. The provided application displays the traffic situation and produces various statistical output on real-time and historical data in oder to analyze frequency utilization and reply rates and investigate anomalities.