***Definition*** :: The airborne portion of the ATC radar beacon system. ***Source*** :: [[PHAK Glossary]] ***Additional Info:*** - [9 Things You Didn't Know About The History Of The Transponder](https://www.boldmethod.com/blog/lists/2016/06/9-things-you-never-knew-about-the-history-of-the-transponder/) from [[Bold Method]] - [[ADS-B and Mode C Requirements.jpg]] #glossary