Regarding the GPS signal, you must be wondering why it is sometimes not available. I make full use of the 21st century Internet information sharing and searches the following points:
1. GPS signal accuracy is directly controlled by the US Department of Defense. The 1.575GHz channel has been supplied to civilian use. Natural or artificial factors of external interference signals will affect GPS signals.
2. Weather factors (sunspots, severe weather such as lightning, rain, and dark clouds will reduce the signal strength, but will not affect the positioning).
3. Electrical electromagnetic interference. Radio and strong magnetic fields will cause different degrees of interference.
4. Under shelters, GPS signals will decrease, such as buildings, cars, insulation paper, trees, metal objects, tin houses, etc.
5. GPS signals have the best reception in open areas. Tall buildings and dense high-rise buildings will refract GPS signals and affect flight stability.