Originally Posted by
India Four Two
Backpacker,
I'm confused. I've never seen a transponder with an altitude display.
Any mode C or S transponder has some sort of altitude encoder built-in, or is slaved from an external altimeter/barometric pressure transducer. It has to, because it has to send the FL to ATC in the interrogation response. Depending on the exact model and display settings, it will simultaneously display the FLs on the display.
Google "Garmin transponder" or "Trig transponder" on Google Images. Plenty results.