Happymodel OVX303 VTX is based on the Open source project OpenVTX powered by JyeSmith (EpxressLRS team)
OpenVTx aims to provide firmware with both the SmartAudio and Tramp protocols. Either protocol can be used on the flight controller and on VTx power up the protocol used is automatically detected by OpenVTx.
Currently SA is fully implemented and test against Rev. 09. To date IMRC has not released a protocol standard and implementation is based on information found within Betaflight.
More info and community
OpenVTX firmware preload
Nano size and stable power output
Frequency: 5.8G 40CH
Transmitting Power: 0/RCE/25mw/100mw/300mw
Power supply: DC 5V
Current (5v): <650ma (300mw)
Weight: 1.5gram without antenna
Center distance of mounting holes: