Ever-present noise

The DECT performance of my Fritz box 7390 is not enough to illuminate every corner of the upper floor of the house. The Fritz DECT repeater should fix this. Instead, however, now with bad reception to get a better reception in the fields, I now had the entire upstairs significantly poor voice quality. Ever-present noise and loud crack accompanied almost every call. And, although I had chosen the location of the repeater so that I there had perfect reception with a telephone.