Verify antenna positioning
Verify the GPS antenna has a clear view of most of the sky and the transmission antenna has a clear view of the satellite. The ideal location for the GPS antenna is high enough to be above everything, but with the shortest cable possible. Cement, steel roofing, or steel walls will restrict or prevent GPS communications.
Check that the transmitter antenna is properly aimed. A poorly aimed antenna will cause a drop in signal strength or possibly prevent successful transmission. As a guide, if the antenna is aimed 20 degrees off the spacecraft, the received power will be half of a properly aimed antenna. Beyond 20 degrees, the received power drops off quickly.
The Device Configuration Utility software has a tool for helping to point the transmitter antenna. Refer to Transmission antenna for more information.