By default channel 13 is not supported as the vast majority of our tables go the US where channel 13 is not allowed. However the fact that it's working at all leads me to believe that channel 13 is enabled on your table.
If channel 13 is already enabled we need to look at potential causes of interference in your environment. Common reasons the table may struggle to maintain a connection are increased interference in a densely populated area, many 2.4 GHz devices in the area or distance from the router. The included radio is not particularly powerful so it's somewhat susceptible to the above issues. Solutions include changing router location, utilizing a 5 GHz band (our more recent tables support 5 GHz) or adding a more powerful WiFi adapter to the table.
If the issue is that channel 13 needs to be enabled there are two ways to do this:
Please respond with more information on the local environment and if one of the listed solutions may work to firstname.lastname@example.org
thank you for your answer. My question was not exact enough. The Fritz!Box is changing the channel from time to time. I think I always lost connection when it changed to Ch13. Because your solutions 1 and 2 are too complicated for me I just set my router to a fixed channel 11. Did not lose connection since.
Thanks and have a merry christmas