Article: Unlike the American GPS, Russian GLONASS, and European Galileo systems, which use medium Earth orbit satellites, BeiDou-1 uses satellites in geostationary orbit. This means that the system does not require a large constellation of satellites, but it also limits the coverage to areas on Earth where the satellites are visible. The area that can be serviced is from longitude 70E to 140E and from latitude 5N to 55N. A frequency of the system is 2491.75 MHz.

Question: What is the frequency of the BeiDou-1 system?
2491.75 MHz