After some research on the internet, I found out that  an 80cm dish is large enough for receiving from and sending to the QO100 satellite. So I went to the local sat store and bought one. Any dish will do, but make sure it is a strong and stable dish. It has to be mounted on a wall or other stable background, because the wind can be very strong and realigning the dish to the satellite during wintertime is not very pleasant.

At first I put the dish on a camera holder, but that didn't work. Not stable enough. So I went back to the local store and got me for only 15 euro's a very strong dish mount bracket for my house wall. Very happy with it. The photo shows the satellite installed to my house.