As I mentioned in my first post about HC-12 433MHz radio modules, I've put my interest in them for telemetry purposes. While S.Port telemetry I'm using in FrSky Taranis radio might have higher range than HC-12, it is closed environment. Since $10 for a pair of HC-12 is not much, I've decided for more open DIY solution.
Setup on a quadcopter consist of one HC-12 configured for FU3 mode and baud rate 9600bps connected to SPRacingF3 UART3 port and "air cooled" (shortened with a coil) 433MHz whip antenna. Well, to be precise, it's 450MHz since I changed working frequency. Antenna is not tuned or scientifically computed. Just 433MHz version shortened a little using proportions. Antenna is mounted on GPS mast. In next version I will probably replace whip antenna with Vee antenna.
Since there is not "ground" in the air, this is probably the weak point of my setup.
"Ground station", or HC-12 to Bluetooth (HC-06 BT module) bridge is powered from 3S LiPo and LM1117 3.3V linear voltage regulator. Here, since size is not an issue, instead of a whip, I used classical half-wave dipole also "more less" tuned to 450MHz.
Here is GPS trace recorded using this telemetry link by EZ-GUI. Max distance from ground station was 450 meters and I did not noticed packet loss. Whole flight was recorded perfectly.
Looks like it works better than expected. HC-12 documentation says that at 9600bps, range should be around 500m. In perfect conditions, open space and so on. Here is was open space, but condition were not perfect. Ground station antenna was pretty low above the ground and UAV altitude was around 10 meters all the time. Well inside 1-st Fresnel zone. Looks promising. Next time I will try to push it a little and test 600m.