Do you have enough distance between your Network Unit and Coverage Unit?
The number on your Coverage Unit tells you the relationship of distance between your two systems. The range is 1-9 with 9 being the greatest distance( a higher number is better).
Just as the interior construction of every building can be very different so can the distance between your Network Unit (NU) and Coverage Units(CU).
Do you have a number between 0-6?
Do you have a number between 7-9?