We were/are considering buying installing a mode-C transponder on our little ELSA. For three reasons: We might want to fly into some class-C airspace, we might want to use flight following, and (because we're fabric covered and don't create a great radar target) would like to be more visible to ATC and other aircraft with radar or ADS-B in.
We just discovered to our dismay that even if we buy a mode-C transponder it won't operate in mode-C (transmitt altitude information) unless it is getting altitude information from an altimeter that is an "encoding altimeter." We're 99% sure our basic steam-gauge altimeter has no such feature.
If we buy and install a mode-C transponder and don't have an encoding altimeter connected to it it then, if I understand right, it can operate in a mode (mode-A?) that would give position info, make us more visible, send our squwak code, but not altitude info. Apparently that would not be sufficient to allow operating in class-C airspace, but would it allow using flight following?
In short, would it be of much use?
And does anyone know if it's possible for a transponder to get altitude info out of our GPS (which reads altitude very accurately)?
Thanks for any replies