Cuav 3DR Radio /MP no constant connection

Hello, everyone,
I have as telemetry the cuav 3DR radio.
However, the connection with Mission Planner is not constant.
At home I booted up the system before driving to the airfield and the connection was established without problems.
30 minutes later at the airfield it was not possible to connect Copter to the notebook without changing any settings.
I had this problem already several times.
Does anyone know the solution for this problem?