Make sure you have the F4 Video setup properly with the same Video Channel as your FPV. I think there are 4 possible video channels. Pick the one that is the clearest on the video screen. The F4 has limited viewing length of about 20 feet. After that range, the F4 Video screen will loose signal and your video screen will be BLUE. If your quadcopter comes back into range, the video screen will activate again. The F7 TX has a range of about 75 feet before the screen turns BLUE.
WALKERA_TX5803
