This is so cool, have started looking into FPV, have ordered a little bit of gear to get started, but this tx will be the start to an on board barometer with a tone.  There are a few vids around showing the setup, but basically it grabs an signal using an Adriouno board which converts it to a tone and sends it to the tx, the tx then pushes the signal to a handheld 433mhz UHF unit.

The video below describes the way to pop it together. No my video, made by a gent called Iforce2d