- for FCC 915MHz it is 75mm
- for EU/LBT 868MHz it is 80mm
From time to time FrSky has a big problem with cutting their antennas to a correct length. Good thing, you can make your own TBS Crossfire RX antennas for cheap!
Do you know that there is a YouTube channel with awesome, drone and FPV related video? Why don't you give it a try?