The AN/APX-121 transponder represents the first application of our vast experience with legacy systems and all the lessons learned to a new product design. This design, combined with the latest technology and manufacturing techniques assures a product that will not only perform to all specified and tested requirements, but will be supportable throughout its life cycle. The AN/APX-121 is one of the highest reliability transponders on the market today with a mean time between failures (MTBF) of 4,400 hours under the extremes of aircraft operating conditions.

AAMSI’s AN/APX-121 transponder is a solid-state, digital design that supports Modes 1, 2, 3/A, C and 4. Additionally, it will support Mode S (ELS). The APX-121 integrates with the 1553B MUX BUS, TCAS via ARINC-429, NSA INFOSEC Applique, KIT-1 INFOSEC, and C-12718/APX RCU. The AN/APX-121 Mode 4 / Mark XIIA Transponder is an improved version of the AN/APX-108. It was specifically designed to incorporate the latest military mandates including Mode S and Mode 4. This modern design eliminates any concern of design or parts obsolescence and provides all new features.

The AN/APX-121 offers clear advantages over other transponders. These advantages include a design architecture that minimizes the number of modules, permits organic maintenance down to the piece-part level for all modules, includes a crypto appliqué for easier maintenance handling, incorporates true digital processing of received and transmitted signals, uses a FLASH memory device to store platform configuration information as well as time-tagged fault data.