The transponer is a Garmin GX23ES and is remote mounted. It is not required to be mounted in the panel. This means I had to find a place to mount it in a very tight area. Not only that but the unit is removable from the tray which means the tray needs to be mounted 10" away from an obstacle. I decided to mount it on angle to the bottom of the panel ribs. Finished. Then I installed the harness I have been working on for the last few days. This includes the audio audio panel, GTN, GTR radio and GTX transponder.