A surveillance receiver for evaluating mode A/C/S activity

When the mode-S transponder was developed, the system was provided with a number of communications capabilities. It was envisioned that a number of enhancements of the modern cockpit would use the mode-S data link. At the time of the development of the mode-S transponder, it was also envisioned that the mode-S transponder would receive a high level of penetration into the secondary radar transponder population because of mandated installation of modes. The mode-S data link is often suggested as an appropriate data link but there are some concerns about the data capacity of the mode-S system. The mode-S system already shares the 1030/1090 MHz frequency pair with ATCRBS transponders and TCAS. Since there is only one frequency pair, every user, world-wide, shares these frequencies. The mode-S system is first, and foremost, a part of the air traffic control radar system and the data link is a secondary operation. Under no circumstances should the data link portion of the mode-S system jeopardize the primary function of the transponder. It was determined that a surveillance system would be an important tool to analyze the amount and type of activity on the 1030/1090 MHz frequency pair. This tool, essentially a recording receiver, would be useful in assessing the potential problems of adding additional loading on the 1030/1090 MHz frequency pair. The receiver design is described and the results of activity tests are presented and compared to previous tests.