Communication lost with RFD900A problem

Hi ,

I use rfd900 for communication link . it is a good link for long range missions . when i conncet PC to plane with mission planner every thing is good and it is 100 % . but when i connect with qgc software percentage of link is 50 % (in .tlog) and every few minutes connection is lost . i changed setting of rfd900 and i tested this firmwares : sik radio 1.6 , 1.13 . But there is still a problem .