It may be caused by one or more of the following reasons:
1. Atmosphere (Ionosphere and Troposphere delay GPS signals);
2. Multipath effect (satellite signal reflected into the receiver antenna through other surfaces);
3. Satellite clock difference and satellite orbit difference;
4. Human interference, such as the US Department of Defense SA satellite signal interference, microwave transmitters, etc.;
5. Weather factors, such as sunspots and bad weather, will reduce the signal strength;
6. Under shelter, such as when the antenna is shielded in buildings or forest trees, under tunnels, overpasses and viaducts, in underground parking lots.
Post time: Nov-30-2019