Dreambox and LNBs

  • Hi
    I have DB7020 running enigma1
    I need to know are there certain types of Lnbs that aren't compatibale with dreambox?
    As I have a problem in recieving many channels with good signal level SNR 88% but I got a small interrupted part of the picture in the upper part of the screen .
    could this be due to Lnb not compatible or dish adjustement or defect in the tuner ??
    thanx